In the late 1990’s, Bill Phillips authored “Body for Life,” which went on to become one of the biggest selling fitness books of all time. In the book, Phillips claimed that performing 20 minutes of high-intensity aerobic exercise (HIIT) after an overnight fast has a greater effect on...
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November 21, 2014
In the late 1990’s, Bill Phillips authored “Body for Life,” which went on to become one of the biggest selling fitness books of all time. In the book, Phillips claimed that performing 20 minutes of high-intensity aerobic exercise (HIIT) after an overnight fast has a greater effect on fat loss than an hour of cardio performed following consumption of a meal. The rationale for the hypothesis was based on research showing that low glycogen levels cause your body to shift substrate utilization away from carbohydrates, thereby allowing greater mobilization of stored fat for energy.
While the theory that fasted cardio is superior for fat loss is certainly intriguing, it is based on an extrapolation of findings that might not translate into practice. Several years ago I authored a review of literature that discussed the contradictions of the research on the topic. While my review highlighted a number of inconsistencies that suggested fasted cardio might not work as claimed, one little issue continued to nag at me: The entire debate was based on acute data; no study had actually investigated the effects of fasted cardio on body fat when subjects were in an energy-deficit sufficient to produce weight loss.
My lab recently carried out a controlled longitudinal trial designed to achieve clarity on the topic. The paper titled, Body composition changes associated with fasted versus non-fasted aerobic exercise was just published in the Journal of the International Society of Sports Nutrition. Here is a rundown of what we found along with a discussion of relevant practical implications.
What We Did
Twenty young non-obese (BMI < 30) were recruited to participate in the study. Prior to the intervention, subjects were tested for body composition (weight, body fat percent, fat mass, fat-free mass, and waist circumference) using a Bod Pod (i.e. air displacement plethysmography), then pair-matched based on initial body mass measurements and randomly assigned to 1 of 2 groups: a fasted training (FASTED) group that performed exercise after an overnight fast (n =10) or a non-fasted training (FED) group that consumed a meal prior to exercise (n =10). These meals were provided in the form of a shake (Pursuit Recovery by Dymatize Nutrition) that contained 250 calories consisting of 40 g carbohydrate, 20 g protein, and 0.5 g fat.
Training was carried out 3 days a week for 1 hour per session on a treadmill. Subjects performed a 5 minute warm-up followed by 50 minutes of walking/jogging at 70% max heart rate. A 5-minute cool down was then provided to end the session. We chose this protocol because evidence shows that lipid oxidation during fasted aerobic exercise is maximized during low-to moderate-intensity steady-state cardio – at higher intensities, the fasted condition allows for an acutely greater lipolysis but the overall oxidation rate is similar to the fed condition because more free fatty acids are available than can be oxidized (in fairness to Bill Phillips, this research came out after publication of his book).
Subjects were provided with customized meal plans intended to bring about a 500-calorie deficit. The meal plans were flexible so that subjects had wide choices of their preferred foods. Protein was kept high to help ensure preservation of lean body mass. Subjects recorded their food in an online web-based program (myfitnesspal.com) on a daily basis so that dietary intake could be continually monitored. Ongoing nutritional counseling was provided to subjects throughout the study period to promote compliance and adherence.
After 4 weeks, the subjects were retested on all body composition measures.
What We Found
Both groups lost a statistically significant amount of weight (1.6 kg vs. 1.0 kg in the FASTED vs. FED groups, respectively) and fat mass (1.1 kg vs. 0.7 kg in the FASTED vs. FED groups, respectively). However, no significant differences were noted between groups in any of the body composition outcomes.
Reconciling Findings with Practical Implications
On the surface, it might seem that the fasted cardio group had a slight advantage in terms of weight loss and fat loss. I’ve seen comments on social media to this effect, claiming a hidden “trend” for a benefit to fasted cardio that our study simply was underpowered to detect.
Fact is, the claim is unsubstantiated.
The p-values (a determinant of the probability that results were due to random chance) were *highly* insignificant, averaging 0.8-0.9 for the various body comp outcomes. Moreover, differences in effect sizes (a measure of the magnitude of the effect) between groups were negligible, further indicating a lack of differences. On top of all that, the FASTED group had somewhat higher (non-significant) baseline body fat percentage, providing a potential advantage for slightly greater fat loss. There are certainly times that I have seen and reported trends in studies I’ve carried out where it was apparent that the small sample size obscured significant differences. That was most definitely NOT the case here. Based on the findings, any differences noted would be attributable to chance — I’d say with a high level of confidence that the sample size was not an issue in this regard.
So does this mean the case is closed and that fasted cardio is worthless for fat loss?
As with every study, there were a number of limitations that must be taken into account when drawing evidence-based conclusions.
For one, the study spanned only four weeks in duration. Certainly this is a sufficient period of time to realize significant reductions in weight and fat mass (as was demonstrated here), but it remains possible that very slight differences between conditions *might* take longer to manifest. We limited the duration of the study in an effort to ensure that the subjects adhered to the diet and exercise protocol (longer term trials in young college students can be problematic with respect to adherence). Our study was not funded, so we could not offer remuneration as an incentive for sticking with the program. Ideally a 16 week protocol would better determine if any small effects would ultimately become significant.
Another potential confounding issue was the use of pre-menopausal women as subjects. Monthly menstrual cycles can influence body weight due to alterations in fluid balance. The fact that pre- and post-testing was conducted exactly one month apart would seem to control for any issues in this regard. However, some women have irregular menses and we cannot rule out the possibility that such fluctuations influenced results.
I will also note that subjects lost slightly less weight than anticipated. This seems to be due to consuming more calories than prescribed in the meal plans. Despite our best efforts to counsel subjects on what to eat and providing detailed instruction on how to to record foods in the online database, the subjects apparently under-reported their nutritional intake. That said, analysis of food diaries indicates that under-reporting was equally distributed between groups and thus this should not have affected overall results. Whether a larger caloric deficit would have provided an advantage to one condition versus the other is open to debate.
Finally, our findings are specific to young, non-obese women and cannot necessarily be generalized to other populations. It has been speculated that the true benefit of fasted cardio is specific to very lean individuals, such as pre-contest bodybuilders, who are trying to lose that last pound or two of stubborn fat. We cannot rule out such a possibility. I’ll note, however, that several of our subjects were off-season track athletes who were quite lean. In fact, four of the subjects (two in each group) had body fat levels that would be considered very low for women (13-16%). When analyzing the results of these four subjects, there was no evidence whatsoever that the fasting condition conferred any benefits. Admittedly this is a tiny sample and certainly cannot be taken as proof of anything. Nevertheless, it does provide a more controlled, objective perspective into potential benefits of fasted cardio than the usual “it worked for me” claims that lack any level of control or objectivity.
A single study is simply a piece in an evidentiary puzzle and can never considered the final word on a topic. What I do think is clear from our study, however, is that if there are any benefits from fasted cardio (still highly equivocal), they would be minor at best. So the best advice for those who are simply looking to get lean is to focus on total energy and macronutrient balance; whether you perform cardio fasted or fed should depend entirely on preference.
On the other hand, it remains possible that a small benefit could be seen by performing fasted cardio. If such an effect does exist, it would seem to be only meaningful to someone who is competing in a bodybuilding or physique competition, where minute differences in fat mass could make the difference between winning or losing a competition. I will point out, however, that it also is conceivable fasted cardio could have a negative effect in this regard. A recent study by Paoli et al showed that lipid utilization over 24 hours was actually higher when eating prior to cardio as opposed to remaining fasted. Thus, the best advice here would be to experiment and try to objectively determine what works best for you as an individual.
October 20, 2014
I recently collaborated with my colleague Menno Henselmans on a review paper that sought to provide clarity on the effects of rest intervals on muscle hypertrophy. Based on the current literature, we concluded that evidence was lacking to support the contention that rest interval length has an impact on growth. Problem is, there have been very few studies carried out to investigate the topic. Thus, it’s difficult to say with any degree of confidence as to whether there are or aren’t any benefits to varying how long you should rest between sets. For more on specifics of the review paper check out my blog post where it is discussed in detail.
Fast forward to today: A new study has just been published titled, Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men that sheds further light on how the duration of rest intervals may affect muscular adaptations. If you just read the abstract, you might think the answer is clear.
Not so fast…
Here’s my take:
22 older men (mean 68 yrs) were recruited for participation. Subjects were healthy but were not involved in resistance training. All subjects underwent a 4-week “break in” phase where they performed a “hypertrophy-type” total body routine consisting of 2-4 sets of 8-15 reps per set. The subjects were then tested for various measures including strength and body composition, and then pair-matched based on 1RM bench press to perform an 8-week strength-type program with short rest (1 minute) or long rest (4 minutes) between sets. The strength-type routine consisted of 2-3 sets of 4-6 reps carried out 3 days a week. The exercises included leg press, flat bench machine chest press, lat pulldown, seated row, dumbbell step-ups, dumbbell Romanian deadlifts, knee extension, and knee flexion. Reps were performed with the intent to move the loads as fast possible while maintaining proper form. All sessions were supervised by trained personnel.
Results were determined over the final 8-week strength phase of the program. Significantly greater increases in fat free mass (FFM), 1RM bench press, and 1RM leg press were noted for the short-rest group compared to those who took long rest periods. The researchers investigated a wide array of additional outcomes including power measures, which also generally favored the short rest group as well.
Based on these results, it would appear that limiting rest between sets is beneficial to enhancing strength and hypertrophy. The increase in FFM for the short-rest group was 1 kg vs just a 0.3 kg increase for the long-rest group. The effect size — a measure of the meaningfulness of the results — was 0.37 indicating a fairly small effect. That said, a difference of 0.7 kg (equating to ~1.5 pounds) could certainly be meaningful for those seeking to maximize hypertrophy — particularly over a fairly short period (8 weeks). The effect sizes for strength were fairly large (0.65 and 0.76 for the 1RM bench and squat, respectively). Combined, these findings indicate that muscular adaptations are enhanced by taking short rest periods between sets.
But…a closer scrutiny of the study’s methodology gives reason for caution when drawing conclusions.
First and foremost, the researchers used DXA to measure body composition. The authors reported results for FFM, which as stated were higher for the short rest group. However, FFM encompasses all tissues in the body other than fat mass. This includes bone, connective tissue, and importantly water. You can probably rule out any differences associated with bone and connective tissue, which almost certainly would be minimal over an 8 week resistance training in terms of contribution to body mass. However, variances in water weight could easily have accounted for a large portion of the the reported 0.7 kg difference in FFM. It’s curious why the researchers did not choose to quantify the subject’s segmental muscle mass. There are equations that can be employed with DXA to obtain these values, which would have given a better sense as to true increases in muscle. Unfortunately, the reported data do not allow for a true understanding of changes in the lean component of body composition between groups.
Second, the subjects did not train to failure in either condition. The researchers stated that this was done to reduce neuromuscular fatigue and thus ensure that the subjects could tolerate the program over its duration. While I have no problem with that reasoning, it does raise a major issue: Since those in the short rest interval group had to lift again after only 60 seconds, they would have been taxed to a greater extent on each successive set. The long-rest group on the other hand would have sufficient time to recover prior to the next set, and thus would not have been substantially taxed at point during the workout. Now it is a bit difficult to determine how much the subjects were actually challenged on each set based on the study write up. Ideally the researchers should have quantified the level of effort exerted (perhaps by RPE or similar scale) to provide context. Without this info, I’m left wondering if the design was biased to produce a greater effect with shorter rest periods.
Finally and importantly, the study was carried out on elderly, untrained subjects. These individuals would no doubt have been sarcopenic, and their response to an exercise stimulus therefore would not necessarily mimic that of young, fit individuals. Thus, generalizability of results is limited to the population studied.
In conclusion, this is an interesting study that adds to the body of literature. However, caution must be exercised when attempting to draw conclusions as to the effects of rest interval length on muscular adaptations. The limitations of the study preclude extrapolation of results to those seeking maximal muscle mass.
The good news is that I am currently collaborating on a study on the topic that directly measures hypertrophy in well-trained subjects. Target completion for data collection is early next year. I will update when results are available.
October 2, 2014
I continue to hear the same claim. It appears in magazine and internet articles. It’s heard in fitness forums and social media outlets. It’s sometimes perpetrated by high-profile fitness pros.
“Just do compound lower body movements and your hamstrings will get all the work they need to grow.”
The statement has been made so many times a lot of folks simply take it as gospel. Problem is, it’s a claim that has no basis.
Let’s talk facts.
First, the idea that hammies would be maximally stimulated in a compound movement doesn’t make sense from an anatomical standpoint. The hamstrings complex as a whole is biarticular, crossing both the knee and hip joints. (Nerd note: the exception is the short head of the biceps femoris, which just crosses the knee and technically is not considered a true hamstrings muscle). At the knee, the hamstrings acts as a flexor; at the hip it acts as an extensor. What happens when you squat down? Try it. The hamstrings shorten at the knee and lengthen at the hip. Alternatively, the opposite occurs on the concentric portion of the movement with the hamstrings lengthening at the knee and shortening at the hip. Thus, the overall functional length of the muscle complex doesn’t change all that much throughout the movement — a phenomenon that is not ideal for maximizing force output.
Research supports the fact that hamstrings activity is low during compound exercise. A recent study from my lab showed that the biceps femoris was only ~25% as active as the vasti muscles and just a third as active as the the rectus femoris during the leg press. Safe to say that the hammies don’t get much work in the leg press.
Think that perhaps squatting shows substantially greater hamstrings activation?
Hamstrings activation during the squat has been shown to be only 27% of maximal voluntary isometric contraction. This led the author of the study to conclude, “Thus the squat is not an optimal exercise for training the hamstrings.”
Okay, so maybe you don’t put much stock in muscle activation and want to put forth the argument that hypertrophy is all that matters. Fair enough. A study by Weiss et al provides direct evidence that squats don’t do much for hamstrings muscle growth. Subjects performed four sets of squats to approximately parallel depth using either a low, medium, or high rep range. Training was carried out 3 days a week for 7 weeks. At the end of the study, results showed significant increases in hypertrophy of the quads for all conditions studied. The hammies: no changes from baseline seen in any of the conditions.
Bottom line: If you want to maximize hamstrings development, you need to incorporate single-joint exercises that directly target the musculature into your routine. Both exercises originating at the hip joint (SLDL, good morning, etc) and exercises originating at the knee (leg curls) are viable choices. Ideally, both types of movements should be combined to optimize growth of the muscle complex.
August 30, 2014
It’s commonly taken as gospel that you need to warm-up prior to lifting. The warm-up contains two basic components: a general warm-up to raise core temperature, and a specific warm-up to heighten neural activation. The combination of these procedures is purported to enhance exercise performance. However, while research does seem to support this contention during maximal or near-maximal efforts, studies are lacking as to the effects of warming up during submaximal lifting routines.
To help determine the impact of warming up on a typical bodybuilding-style workout, I recently collaborated with colleagues in Brazil to carry out a controlled study on the topic. Here is an overview of the methodology and findings of the study, as well as its practical implications.
What We Did
Fifteen young men were recruited to participate in the study. Subjects were “recreationally trained” meaning they had limited lifting experience (resistance training for less than a year on average). Each subject performed 4 exercise sessions on separate days (48-72 hours between sessions) using the following different warm-up strategies prior to each workout: a general warm-up; a specific warm-up; a combination general and specific warm-up, or; no warm-up. In the aerobic warm-up subjects performed 10 minutes of light cycling exercise at a speed of 40 km/hr. For the specific warm-up, subjects performed a light set (10 reps at 50% 1RM) of the specific exercise before performance of that exercise. The order of the warm-ups was counterbalanced between subjects as shown in the accompanying figure to ensure that this variable did not unduly influence results. Exercise sessions consisted of 4 sets of the bench press, squat and arm curl at 80% 1RM. All sets were carried out to the point of muscular failure.
What We Found
There were no significant differences between the number of repetitions performed in any of the warm-up conditions nor was their a difference in the fatigue index, which is a formula that assess the decline in number of repetitions across the first and last sets of each exercise. In combination, these findings indicate that the warm-up procedures analyzed in this study had no effect on performance.
At face value it would appear that a warm-up is pretty much useless prior to submaximal resistance training. Despite the currently held belief that warming up enhances exercise performance, no benefits were seen between either a general warm-up, specific warm-up or combination of the two compared to no warm-up at all. Intuitively this seems to make sense in that the initial repetitions of a submaximal lifts are in effect their own specific warm-up and the need to increase core temperature might be superfluous from a performance standpoint when multiple reps are performed.
When applying these results to practice, however, several factors must be taken into account. First, the subjects in this study were recreationally trained; although they had some experience with resistance training they were in no way highly skilled lifters. It certainly is feasible that those with extensive lifting experience who have highly developed neuromuscular patterns might benefit from even slightly increased neural responses.
Second, you need to take into account the type of exercise performed. To this point, there did seem to be a slight advantage to performing a specific warm-up in the squat (although it did not rise to statistical significance) while there actually seemed to be somewhat of a detriment to the specific warm-up in the biceps curl. Thus, more complex movement patterns would seem to benefit from the “practice effect” of a specific warm-up while this would be of no value during performance of simple exercises.
Third, the absolute amount of weight lifted also must be considered. A good case can be made that a specific warm-up would have more utility for someone benching 400 pounds as opposed to 200 pounds. Even though the “heaviness” of the load would be similar on a relative basis, the neural benefits of doing a lighter set would seem to have greater transfer when lifting the heavier absolute load.
Finally, we did not investigate safety-related issues of warming up — only performance-aspects were assessed. Although no subjects in this study were injured during testing, the sample was too small and the duration of the protocol too short to draw conclusions on the topic. While resistance training with submaximal loads generally has very low risk of injury provided proper form is maintained, there nevertheless exists the possibility that warm-up procedures could reduce the risk even further. This seems especially pertinent when working with high absolute loads.
The take-home message is to consider your own situation when determining whether or not to warm up prior to a submaximal lifting session. Yes, a warm-up does take a bit of time and you might be able to skip the procedure if you are time-pressed without enduring any negative effects on performance. This is particularly valid if you are less experienced at training and/or lifting fairly light loads. On the other hand, if you are a highly experienced trainee lifting heavy absolute loads then there very well might be a benefit to warming-up — this study certainly cannot be used as evidence to the contrary. Also, understand that research only reports the means (i.e. averages) between groups. There were in fact differences between responses whereby some subjects did show a beneficial effects from warming up while others did not. Only through individual experimentation can you determine if a warm-up enhances your own performance. Finally, there are potentially safety issues that were not studied here; a warm-up certainly would not seem to hurt in this regard and possibly could be of some help.
Ribeiro AS, Romanzini M, Schoenfeld BJ, Souza MF, Avelar A, Cyrino ES. Effect of different warm-up procedures on the performance of resistance training exercises. Percept Mot Skills. 2014 Aug;119(1):133-45.
August 17, 2014
Wanted to update everyone on all that’s been happening; so much to share!
First, I’ve agreed to write a textbook on muscle hypertrophy, to be published by Human Kinetics — one of the leading publishers on the science of exercise and nutrition. The book will be geared towards fitness professionals and university programs. I’m totally stoked to provide an evidence-based resource on a subject that has long relied on gym lore and bro-science. Estimated pub date is April of 2016.
I’ve also agreed to write a monthly column for Flex Magazine. The column will discuss science-based application of hypertrophy and fat loss practices. It’s a real kick for me to be a regular columnist for a mag that I grew up reading. My first column is slated for the November issue.
Research-wise, I’m currently finishing up a study on body comp changes associated with fasted cardio and another on muscle activation during different loading intensities in the bench press. During the fall I have multiple studies set to get underway including a training frequency study investigating muscular adaptations in split vs. total body routines, another comparing functional transfer between the squat and leg press, and yet another that will evaluate the effects of protein timing pre- versus post-workout on muscle hypertrophy in well-trained subjects. I look forward to sharing the results of these and other studies currently in review when they become available.
Okay, that out of the way, here are some links that I thought you’d find informative. As always, I appreciate your continued support.
• I recently lectured at the CanFitPro Conference in Toronto. While there, I got a chance to record a few interview segments for Omar Isuf’s YouTube channel. In this segment we discuss repetition ranges for maximizing muscle hypertrophy. Give this a watch and you’ll see why Omar lives up to his nickname, King of YouTube Fitness.
• I was interviewed along with my partner-in-science, Alan Aragon, on the We Do Science Podcast. Here Alan and I discuss the complexities of nutrient timing, delving into both the science and practical applications on the topic. Bonus discussion on a related topic: whether there is any fat loss benefit to doing fasted cardio. Click on Episode #8.
• I’ve appeared numerous times on Superhuman Radio; this segment might be my favorite yet. Here I discuss whether it’s possible to gain muscle simultaneously while simultaneously losing fat. Host Carl Lanore is consistently one of the best interviewers in the biz and he again shows why by asking all the right questions. l
• My friend and colleague Tom Venuto wrote an excellent post on delayed-onset muscle soreness and its relevance to muscular gains. The article covers the science in an understandable fashion, and provides solid take-home advice.
• Speaking of Tom Venuto, he wrote what I think is the most detailed review of my book, The M.A.X. Muscle Plan. Always an honor to receive praise from a true fitness pro such as Tom.
• In case you missed it, I recently published this study showing muscle activation during the leg press at 30% 1RM to failure produced significantly lower muscle activation compared to 75% 1RM. I also wrote an accompanying blog post where I break things down into consumer-friendly language and discuss the study’s implications.
• Finally, my good friend Bret Contreras wrote this terrific article that delved into the free-weights vs. machines debate. As mentioned earlier, I will be collaborating on a study examining this topic; Bret’s post provides excellent commentary on its complexities. While you’re at it, make sure to read through the references at the end of the article; it’s patently clear research doesn’t support the claims made by certain fitness pros.
August 13, 2014
There is compelling evidence that the onset of fatigue during resistance training results in an increase in motor unit activation, whereby the strength-oriented type II fibers are progressively recruited to sustain muscular contractions. Some have taken this to mean that any load, regardless of how light, will ultimately lead to full fiber recruitment provided that training is carried out to muscle failure (i.e. the point where you are unable to complete an additional rep with proper form).
Recently, my lab sought to test this hypothesis. Here is an overview of the study and its practical implications. The study, titled, Muscle activation during low- versus high-load resistance training in well-trained men, was just published ahead-of-print in the European Journal of Applied Physiology.
The purpose of the study was to compare muscle activation in the leg press at 30% and 75% 1RM when sets are carried out to muscular failure. Ten college-aged men were recruited for participation. Subjects were all experienced in resistance training, including regular performance of lower body exercise.
A within-subject design was employed where each participant performed both 30% and 75% 1RM conditions. Testing was carried out over two sessions. Subjects were initially tested to determine their 1RM in the leg press. They then returned to the lab at least 48-hours later for muscle activation testing of the quads (rectus femoris, vastus lateralis, and vastus medialis) and the hamstrings (biceps femoris) during heavy- vs. light-load training. The order of performance was counterbalanced whereby Subject 1 performed the high-load condition first, Subject 2 performed the low-load condition first, etc. In this way, we ensured that order of performance did not confound results. Fifteen minutes rest was provided between trials to ensure that previous fatigue was not a factor. We verbally encouraged subjects to perform each set to the point where they could physically no longer continue training with proper form.
Both mean and peak muscle activation was markedly and significantly greater during the heavy- compared to light-load condition (by 57% and 29%, respectively). Importantly, not a single subject displayed equal or greater activation during low-load training. These findings strongly suggest that training at 30% 1RM in a compound lower-body exercise is insufficient to recruit the entire motor unit pool for the target musculature.
It has been well-established that training to muscle failure causes an increase in motor unit recruitment. This outcome was in fact confirmed in our study, as EMG amplitude increased in both the high- and low-load conditions over the course of each set. However, the magnitude of these increases were substantially lower during light- versus heavy-loading. The take home message here (in conjunction with a recent study on the topic using single-joint lower body exercise) indicates that a minimum threshold exists to achieve activation of the full spectrum of fibers and that 30% 1RM is below this threshold. Thus, it can be inferred that some of the highest threshold motor units — those associated with the type IIx fibers — were not recruited during the low-load condition.
From an applied standpoint, it might seem that these findings show training at very low-loads is useless. After all, why would you train with a load that does not generate complete fiber recruitment, right?
Not so fast.
Understand that there are two aspects to maximizing muscle development: recruiting a fiber and then keeping it stimulated for a sufficient period of time (i.e. time under load). While the loading strategy used in the light-weight condition here (i.e. 30% 1RM) did not bring about full muscle activation, it did maintain tension in the lower-threshold motor units for an extended time period. This could be particularly important in optimizing development of the type I fibers that are highly fatigue-resistant. This lends credence to the hypothesis that training throughout the full spectrum of rep ranges is the best strategy for maximal muscle hypertrophy. I have a longitudinal training study currently in review that seems to support this hypothesis. More on that in the near future.
An interesting secondary finding of the study was that the hamstrings displayed only minimal activation during the leg press — much less than that seen in the quads. This refutes the claims by some fitness pros that single-joint exercise is unnecessary provided you perform compound lower body exercises. Our results clearly indicate that movements such as the leg curl, stiff-leg deadlift, and good morning are important components of a well-rounded resistance training program to ensure proper symmetry between the quads and hamstrings.
A limitation of the study is that we only assessed a single set at each condition. Thus, it is not clear whether accumulated fatigue from performing multiple light-load sets would ultimately bring about complete recruitment. This requires further study. But even if this turns out to be the case — which is far from a certainty — it would mean that you’d need to perform a lot of additional volume just to achieve similar levels of activation; at the very least, an inefficient training strategy.
I am in the process of finishing a follow-up bench press study looking at 80% vs. 50% 1RM in an attempt to determine the approximate minimum threshold necessary for complete muscle activation. This will provide important info to those who are unable to lift heavier weights due to medical conditions or other issues. Realize, though, that muscle activation (and hypertrophy for that matter) do not necessarily translate into optimal strength gains. My recent study showed that even moderate load training (~10 RM) is inferior to very heavy lifting (~3 RM) if absolute strength is the goal. I discussed that study in-depth in this blog post
On a side note, I’ll be discussing the ramifications of this study and others currently in progress at my upcoming seminar in Montreal next month. Hope to see you there!
Cook SB, Murphy BG, Labarbera KE. Neuromuscular function after a bout of low-load blood flow-restricted exercise. Med Sci Sports Exerc. 2013 Jan;45(1):67-74.
Schoenfeld BJ, Contreras B, Willardson JM, Fontana F, Tiryaki-Sonmez G. Muscle activation during low- versus high-load resistance training in well-trained men. Eur J Appl Physiol. 2014 Aug 12. [Epub ahead of print]
Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Tiryaki-Sonmez G, Alvar BA. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. J Strength Cond Res. 2014 Apr 7. [Epub ahead of print]
August 11, 2014
Science is ever-evolving. New studies are continually carried out to expand on previous research and thus shed additional light on topics of interest. The process can be likened to solving a puzzle, where more and more pieces are provided over time to ultimately fill out the complete picture.
Such is the case with a recently published study titled, Effect of timing of protein and carbohydrate intake after resistance exercise on nitrogen balance in trained and untrained young men. Briefly, the study employed a within-subject design where both an untrained group and a trained group performed regimented resistance training under two different protein-timing conditions. Training was carried out over two consecutive 11 day periods using a push/pull split (lower body on days 1, 5, and 9; shoulders, chest, and triceps on days 2, 6, and 10; back and biceps on days 3, 7, and 11). Subjects were placed on a regimented nutritional plan where they ate breakfast at 7 am, lunch at 1 pm, and dinner at 7 pm. During one of the 11-day training phases subjects consumed a protein supplement immediately after exercise while during the other phase they consumed the shake 6 hours post-workout. Importantly, training was carried out from 10 to 11 am each morning prior to lunch. The table below provides specifics on the study’s protocol.
The results were intriguing. In the untrained group, no differences in nitrogen balance were noted between timing strategies. Conversely, the trained subjects showed a significantly greater positive nitrogen balance when protein was provided immediately after training compared to delaying consumption by 6 hours.
Upon first hearing about the study I was ready to dismiss results because of the very long wait to consume the post-workout supplement. Considering that training was carried out 3 hours after breakfast and that training took an hour, that means the supplement was ingested 10 hours after breakfast. Simple logic dictates that’s not ideal if the goal is to maximize the anabolic impact of training.
Here’s the rub though: Subjects ate lunch 2 hours after the training bout and that meal contained ~30 grams of protein. So in essence, the study actually showed that delaying intake just a couple of hours after a training bout had a significantly detrimental effect on protein balance in experienced lifters.
With that as background, here are some things to keep in mind when drawing evidence-based conclusions. I’ll start by noting that the study was well-designed to assess the desired outcome measure (nitrogen balance). The author took good care to control all relevant variables, in particular food intake (diets were designed by a nutritionist and intake was strictly monitored). This provides good confidence that results were attributed to the independent variable — namely, timing of post-workout protein provision.
It is important to understand, however, that the study measured nitrogen balance over a 3 day training period — not long-term muscle growth. Now there is a correlation between *chronic* nitrogen balance and hypertrophy. The accretion of muscle proteins is predicated on a positive nitrogen balance, whereby protein synthesis exceeds protein breakdown over a given time-frame. However, it is misguided to extrapolate that an *acute* measure of nitrogen balance will necessarily translate into greater muscle hypertrophy over the course of weeks or months. To this point, recent research from Stu Phillips lab shows that acute measures of post-exercise protein synthesis do not correlate well with long-term increases in muscle growth.
In addition, the nitrogen balance technique itself has inherent limitations. Research has shown that the technique results in an overestimation of nitrogen intake and an underestimation of nitrogen losses. Moreover, its ability to accurately determine balance over short time frames has been called into question — and this study evaluated balance over a period of just 3 days. Finally, nitrogen balance comprises many bodily tissues and thus it is not clear if differences are specific to muscle fractions. Whether these factors had an impact on the present study is anyone’s guess. Therefore, results must be interpreted cautiously.
Bottom line is that the study provides some interesting insight for generating hypotheses. In the narrative review I co-authored with Alan Aragon, we discussed that the anabolic effects of a meal last a maximum of about 6 hours, and therefore speculated that this would be the outer limit as to how long you should wait to consume post-workout protein from the time of your last meal. The present study suggests waiting 6-hours between meals has a negative effect effect on protein accretion in trained subjects but not in untrained subjects. Whether this translates into reductions in long-term muscle mass is unknown and can only be determined from a longitudinal study that directly measures changes in muscle hypertrophy.
Fortunately, I am collaborating with Alan Aragon and Colin Wilborn a study set to begin in a few weeks that will investigate this very topic. Stay tuned!
Aragon AA, Schoenfeld BJ. Nutrient timing revisited: is there a post-exercise anabolic window? J Int Soc Sports Nutr. 2013 Jan 29;10(1):5.
Mitchell CJ, Churchward-Venne TA, Parise G, Bellamy L, Baker SK, Smith K, Atherton PJ, Phillips SM. Acute post-exercise myofibrillar protein synthesis is not correlated with resistance training-induced muscle hypertrophy in young men. PLoS One. 2014 Feb 24;9(2):e89431. doi: 10.1371/journal.pone.0089431. eCollection 2014. Erratum in: PLoS One. 210;9(5):e98731.
Mori H. Effect of timing of protein and carbohydrate intake after resistance exercise on nitrogen balance in trained and untrained young men. J Physiol Anthropol. 2014 Aug 6;33(1):24. [Epub ahead of print]
Rand WM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. Am J Clin Nutr. 2003 Jan;77(1):109-27.
Tomé D, Bos C. Dietary protein and nitrogen utilization. J Nutr. 2000 Jul;130(7):1868S-73S. Review.
August 2, 2014
The beauty of peer-reviewed research is that it’s self-correcting. Scientists publish papers and then the scientific community scrutinizes the methodologies and conclusions employed. When appropriate, criticism is levied on a study and discussion/debate ensues. This process should be welcomed by researchers; it’s what pushes science forward and enhances our understanding of a given topic.
As many of you know, an area of research that I’ve recently been pursuing is the effects of protein timing on muscle strength and hypertrophy. In 2013 I collaborated with my good friend and colleague Alan Aragon to publish a review on the topic titled, Nutrient Timing Revisited: is there a post-exercise anabolic window?. In short, our review concluded that while muscle is sensitized to anabolism in the post-workout period, current evidence does not seem to support the existence of a narrow “window of opportunity.” I discussed the practical implications of the review in a previous blog post.
The paper stirred a lot of controversy. After all, the concept of an anabolic window of opportunity for nutrient consumption had been somewhat of a sacred cow in the field. Until publication of our review it was widely taken as gospel that you had an hour or less to take advantage of this narrow window; if you missed the window, muscular gains would be compromised.
One of the staunchest proponents of the nutrient timing paradigm is Dr. John Ivy, a professor at the University of Texas and noted sports nutrition researcher. Dr. Ivy literally wrote the book on nutrient timing with publication of his popular text, “Nutrient Timing: The Future of Sports Nutrition” back in 2004 It therefore was no surprise that Dr. Ivy took issue with our paper in an article he published in the American Journal of Lifestyle Medicine.
I welcomed Dr. Ivy’s criticism of our paper. As stated, critical debate of research is what drives science forward. But debate is a two-way street. I felt his critique was heavily biased and that he cherry-picked research to substantiate his claims.
As such, I provided a point-by-point rebuttal to Dr. Ivy’s critique in this blog post. In an effort to be fair and balanced, I emailed Dr. Ivy and gave him the opportunity to write a response to my comments. I offered to post anything he wrote unedited on my blog; unfortunately he never responded to my offer.
Subsequently, I co-authored a meta-analysis on protein timing with Alan Aragon and another good friend and colleague, James Krieger, titled The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Results showed a small effect for protein timing on hypertrophy, but virtually the entire effect was explained by an increased protein intake in the timing group. I discussed the study in detail in this blog post.
This week Dr. Ivy took to the airwaves to levy criticism of our meta-analysis. Appearing on the Superhuman Radio Network, Dr. Ivy called our paper “flawed” and took several of our methods to task (the discussion of our paper comes in at about the 22 minute mark).
Suffice to say, it’s my view that Dr. Ivy’s criticisms lack merit. What follows is a point-by-point refutation of Dr. Ivy’s claims.
First, Dr. Ivy mentions that “good studies were eliminated from the analysis” In particular, he specifies two studies that didn’t make the cut because they did not provide enough protein for inclusion in the analysis. He goes on to states that “…these studies showed significant increases in strength and muscle mass, so I don’t know how you can say that the protein wasn’t effective.”
I’ll start by saying that meta-analysis is only as good as the data it analyzes. Thus, rigid inclusion/exclusion criteria must be established to focus the analysis on the topic at hand.
Our inclusion criteria mandated that studies had to provide subjects with at least 6 grams of essential amino acids (EAAs). This cutoff point was determined from research showing that a ~6 g dose is required produce a marked increase in net protein balance – double the magnitude compared to a 3 g dose. If we had allowed inclusion of lesser amounts of post-workout EAAs intake it could just has easily been claimed that any negative findings would be attributed to insufficient protein provision.
That said, Dr. Ivy makes a fair point here since some potentially relevant studies were omitted from analysis. So let’s look at the two studies he mentioned.
In perhaps the most heralded study by protein timing proponents, Esmarck et al. randomly assigned 13 elderly men (average age 74 years) to perform a resistance training protocol 3 days a week for 12 weeks. The only variation in the protocol was that subjects consumed 10 grams of protein (a combination of skimmed milk and soy protein) either immediately following or 2 hours after the exercise bout. Results showed that muscle cross sectional area and mean fiber area of the quadriceps increased by 7 and 22 %, respectively for the group that received protein immediately post-exercise while the group that delayed protein intake showed no increases in fiber hypertrophy. On the surface, these findings would appear to provide compelling evidence in support of a narrow anabolic window of opportunity. Nail-in-the-coffin evidence, right?
Not so fast.
It is highly curious that the delayed-intake group saw *no* gains in muscle growth over a period of 12 weeks regimented resistance training simply because they waited 2 hours to consume protein. Zero! Considering that virtually every resistance training study ever done shows significant hypertrophy in untrained subjects after 3 months of regular lifting, the results must be viewed with skepticism. Moreover, these results were achieved with a dose of just 10 grams of protein (including lower quality soy protein), which equates to ~3 grams of EAA –an amount that as mentioned promotes only half the increase in protein synthesis as our required 6 gram dose. Add to this the fact that elderly subjects tend to be protein insensitive and generally need a ~40 gram dose to fully stimulate muscle protein synthesis and the findings are even more suspect. I’ll also note that the study had a very small sample size (only 7 subjects in the immediate provision group and 6 in the delayed consumption group), limiting statistical power. All told, it’s hard to make a case that this is nail-in-coffin evidence in favor of protein timing.
The other study we omitted because protein intake fell below the 6 gram threshold was carried out by Holm et al., who evaluated the effects of protein timing in 29 postmenopausal women over 24 weeks of resistance training. After exercise, subjects consumed a supplement containing either 10 grams of protein or placebo in double-blind fashion. Results showed that group who received the protein dose after exercise displayed greater gains in lean body mass compared to the placebo group. Interestingly, MRI analysis conducted at the 12-week midway point showed no differences in hypertrophy between groups (unfortunately the MRI was not repeated at the end of the study so it can’t be determined whether results would have diverged over time). While on the surface this study does provide some support for a beneficial effect of timing, it is important to note that total daily protein intake was ~10 grams greater for the timed group, and this confounding variable could have been responsible for any differences in muscle mass as opposed to a direct impact from timing.
Dr. Ivy also neglects to mention that two other studies were ultimately omitted from our analysis because we were unable to obtain sufficient data to compute an effect size. One of these studies by Bemben et al. showed no differences from a timed dose of protein compared to a non-timed dose. The other study by Burk et al. actually found a superior response when protein was consumed early in the day and late in the evening as opposed to before and after a workout.
Considering all the above, it is a huge stretch to claim that our inclusion/exclusion criteria unfairly biased results. The two studies excluded because of low protein provision had substantial limitations that deserve real scrutiny, and when factoring in the other two studies excluded for lack of usable data the net effect is at best a washout.
Next, Dr. Ivy stated we included studies that were not truly looking at nutrient timing but rather looking at differences between supplements post-exercise. He states these studies didn’t eliminate supplements post-exercise they just used different types of supplements. To quote Dr. Ivy: “They used studies that did not restrict eating post-exercise. For example, they would use studies where one group was given a protein supplement and the other was given an isocaloric carbohydrate supplement.”
While Dr. Ivy’s basic point is true, I’m not clear as to what the beef is here? Our inclusion/exclusion criteria specified we’d include any and every randomized controlled study where at least one treatment group consumed a minimum of 6 g EAAs < 1 hour pre- and/or post-resistance exercise and at least one control group did not consume protein < 2 hours pre- and/or post-resistance exercise. It really doesn’t matter whether or not protein timing was the primary objective of the research hypothesis per se. As long as a study employed timing in the manner specified by inclusion/exclusion criteria, then it provides a valid basis for evaluating the effects of timing. If I'm missing something here I'd be happy to hear Dr. Ivy's rationale.
Dr. Ivy goes on to question our statistical methods. He states: “In a meta-analysis you do what’s called an effect size on each of the independent studies. There were certain studies like the one by Cribb and Hayes which have dramatic differences between the groups that had supplementation around the workout versus in the morning and evening. When I looked at the effect size I thought it would be huge but it wasn’t. So I’m not sure how they actually measured the effect size, which can affect the results as well.”
This is a curious comment as the statistical calculation of effect size is clearly stated in the methods section of our paper. The formula is plainly presented so that anyone can easily perform their own calculations. We’re certainly happy to address any discrepancies in statistical outcomes based on hard data that conflicts with we found. However, it’s unscientific to simply dismiss our findings because they don’t conform to individual expectations based on intuition.
Finally, Dr. Ivy insinuates that we included a lot of poor quality studies and states if you look at lean body mass gains in the “6 or 7 good studies” — the ones he considers to be “well controlled” – then a clear superiority emerges for protein timing.
While Dr. Ivy is certainly entitled to his opinion as to what represents a “good” study, I’ll note that we did a quality analysis using the PEDro scale. The average PEDro score of the studies was 8.7 (out of a possible 11) indicating a very high degree of quality. I have scrutinized the quality between studies showing an effect of protein timing versus those that did not, and see no major differences between the two. Again, if he feels that the pro-timing studies are of sufficiently higher quality than those showing no effect then he needs to provide specifics. It’s not enough to make a passing statement such as this without backing up claims with supporting evidence.
As mentioned in a previous post, I have a great deal of professional respect for Dr. Ivy. He is an esteemed researcher and has a long history of publishing quality studies. However, a researcher’s body of work doesn’t provide a mandate to accept his opinion as fact.
When scrutinizing research, it is imperative that we take an objective approach; personal bias should never enter into the analysis. If Dr. Ivy wishes to criticize our meta-analysis, he must do so in the context of the overall body of literature rather than with evidence that selectively supports his opinion. Otherwise, the critique comes across as a skewed attempt to discredit the study for the purpose of confirmation bias. I’ll again put the offer out there for Dr. Ivy to write a response, which I will publish unedited in its entirety.
I’ll conclude by noting that I will soon be collaborating on a protein timing study that should help to fill in some of the many gaps in the literature, with data collection set to begin next month. Neither I nor my co-authors have any stake in the topic. I’ll be happy to consider changing my opinion on the topic in the face of compelling evidence.
Bemben MG, Witten MS, Carter JM, Eliot KA, Knehans AW, Bemben DA. The effects of supplementation with creatine and protein on muscle strength following a traditional resistance training program in middle-aged and older men. J Nutr Health Aging. 2010 Feb;10(2):155–159
Børsheim E, Tipton KD, Wolf SE, Wolfe RR. Essential amino acids and muscle protein recovery from resistance exercise. Am J Physiol Endocrinol Metab. 2002 Oct;283(4):E648-57.
Esmarck B, Andersen JL, Olsen S, Richter EA, Mizuno M, Kjaer M. Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans. J Physiol. 2001 Aug 15;10(Pt 1):301–311
Holm L, Olesen JL, Matsumoto K, Doi T, Mizuno M, Alsted TJ. et al. Protein-containing nutrient supplementation following strength training enhances the effect on muscle mass, strength, and bone formation in postmenopausal women. J Appl Physiol. 2008 Jul;10(1):274–281
July 27, 2014
Here is episode #9 of the B&B Connection. Bret and I discuss some of our recent research collaborations as well as touching on the just-pubbed review I co-authored with Menno Henselmans. Here are links to a few of the studies discussed (two are not yet availabile — one is still in press and the another in review).
July 26, 2014
Few nutritional topics spark more debate than the efficacy of low-carb diets. It’s therefore no wonder that a recent meta-analysis titled Low Carbohydrate versus Isoenergetic Balanced Diets for Reducing Weight and Cardiovascular Risk: A Systematic Review and Meta-Analysis is currently stirring up quite a bit of controversy in internet forums and social media outlets.
In case you’re not aware, a meta-analysis involves pooling the results of studies on a given topic to achieve clarity on the body of evidence. Here is an overview of the study with my analysis of methods and findings as well as commentary on its implications:
An important component of a meta-analysis is the inclusion/exclusion criteria. Simply stated, this refers to what conditions must be met for studies to be included in the analysis. For this meta-analysis, researchers required that studies had the following constraints:
• Compared a “low-carb” diet (less than 45% of calories from carbs) to a “balanced” diet (45-65% calories from carbs) that were isoenergetic (same number of calories between groups) in randomized, controlled fashion
• Comprised overweight or obese subjects
• Included macronutrient breakdowns
• Spanned at least 12 weeks in length
• Contained at least 10 subjects in each group
For statistical analysis, the low-carb diets were stratified into “high fat” (containing greater than 35% lipid) or high protein (containing greater than 20% protein). The diets were then further stratified into those where subjects were type 2 diabetics or non-diabetic. This stratification allowed for sub-analysis in a manner that helped reduce the potential confounding.
At first glance it would be fair to question the fact that “low carb” was categorized as any diet containing less than 45% of total calories. However, percentages can be misleading. The only truly relevant number here is the total grams consumed from carbohydrate. Let’s take a look at how this factored in to the included trials.
For the high-fat, non-diabetic studies there was one true ketogenic diet (4% of total calories from carbs) and the others ranged between 26-38% total calories from carbs. Given that energy intakes varied from about 1500 – 1700 calories per day, this puts total carb intake at about 97 to 161 grams/day (discounting the one true keto study). On the lower end this would put most in ketosis while on the higher end it would not. Carb intake in the high-fat diabetic studies averaged 20% of total calories, which would almost certainly translate into a ketogenic state in these subjects. The “high-protein” studies were basically all “Zone” type diets using the 40-30-30 approach. In these studies the total carb intake would have been greater than 150 grams and hence not induce ketosis. Bottom line: The “high fat” groups could fairly be classified as low-carb for the most part (at least if you pool the means of these studies) while the “high protein” groups would be more appropriately placed in a balanced category.
Overall the inclusion criteria allowed for the ability to examine an important issue on the topic, namely the effects of carb intake when total calories are kept constant. As will always happen in such situations, a number of studies that can have relevance are ultimately excluded from analysis. The extent to which this impacts results cannot be determined and the entire body of literature should always be taken into consideration when drawing evidence-based conclusions for practical application to nutritional approaches.
A total of 19 RCTs met inclusion criteria encompassing 3209 participants. The duration of the studies spanned from 3 months to 2 years. In scrutinizing the methodology, the researchers appeared to have done a nice job collecting and analyzing data. Two different researchers were involved in the search and coding process. This serves as a double-check to help minimize the prospect of errors in data entry. They screened for various types of bias (i.e. selection, performance, detection, attrition, and reporting) and did report instances where these issues could have impacted results. The one thing I did not see mentioned was an attempt to re-code a random number of the studies to check for “coder drift” (a change in the interpretation of coding items over time). It’s unlikely that this significantly impacted results, but the possibility cannot be ruled out based on what is presented in the methods section.
There were no significant differences in any of the outcomes at any of the time-points measured; weight loss was similar between all of the diets as were health-related outcomes (blood pressure, blood lipids, fasting glucose). The forest plots highlight the disparity between studies, with no trend whatsoever for superiority of one diet over another. The evidence presented suggests that when calories are equated, there is no difference in weight loss or health-related markers regardless of carbohydrate intake.
The primary limitation of the analysis is the fact that participants did not fully adhere to prescribed macronutrient goals in a majority of trials, and adherence declined with longer time periods. Compounding matters further, self-reporting of food intake is historically inaccurate, particularly in those who are overweight and obese. Thus, the strength of evidence is compromised here, making it is difficult to formulate clear conclusions from the analysis.
On the other hand, what is reinforced from this data is just how difficult it is to stick with a diet – any diet – over the long-term. As the authors of the study point out, this is especially true in diets that exclude entire food groups such as low-carb diets (although it should be noted that adherence in the balanced diet was equally poor in the studies analyzed). With respect to weight loss, nothing is more important than dietary adherence; you can’t achieve results if you don’t follow the diet.
The other point to keep in mind is that the subjects were all overweight or obese. Thus, results cannot necessarily be generalized to a healthy, non-overweight population. Now I’d point out that those who are lean tend to be more insulin-sensitive compared to the overweight/obese, and therefore low-carb diet would seemingly have less utility for these individuals. This would be particularly true of those who are serious exercisers, as both aerobic exercise and resistance training enhance insulin sensitivity. Still, the relevance of findings to lean or athletic populations remains questionable.
This meta-analysis provides evidence that energy balance – not macronutrient composition – is what dictates weight loss, although findings must be interpreted with caution due to poor dietary adherence across protocols. Despite this inherent limitation, results seem to be consistent with current theory on weight loss. While ketogenic diets can be a viable approach for some, I’m aware of no evidence showing that they have a universal metabolic superiority over balanced diets provided calories and protein are equated between dietary strategies. In fact, the few studies that have investigated the topic under controlled conditions failed to show any such metabolic advantage:
• Johnston et al compared a ketogenic diet (33 g carbs) to a balanced diet (157 g carbs) in a sample of 20 sedentary overweight/obese men and women. Total protein and calorie consumption were held constant so the only thing that differed between diets was intake of carbohydrate. No differences were found in fat loss or markers of cardiovascular health. The big strength of this study was that all meals were individually prepared giving a high degree of confidence in the results. The study was limited by a duration of only 6 weeks and a small sample size.
• Soenen et al. conducted an elegant study that included four isoenergetic groups of varying protein and carb content, including groups where protein was matched but carb intake varied. The study was carried out over a 12 month period with an initial 3-month phase where subjects consumed 33% of their maintenance calories followed by a 9-month phase where subjects consumed calories at 66% of maintenance. During the initial 3-month phase the low-carb group consumed 5% of calories from carbohydrate; during the second phase carb intake increased to 25% of total calories. The average total caloric intake was not disclosed, but given the percent carb values and the fairly substantial energy restriction, it would certainly appear that the subjects were in ketosis throughout the study duration. Results? Here is a direct quote from the authors: “The study showed irrefutably, that, despite the success all-over with all four diets, the answer is that it is the relatively high-protein content per se, that supports the even greater success, and not the relatively lower carbohydrate content.”
The primary take-home message here is that there is no universal “best” diet. There is compelling evidence that higher protein intakes (at least 1.5 g/kg and generally higher in those who are lifting weights) are beneficial for optimizing body composition and enhancing satiety. A certain amount of dietary lipid is also essential for proper health, particularly with respect to polyunsaturated fats. Otherwise your approach to nutrition is largely an individual choice that, within fairly wide limits, should be based on preference, goals and lifestyle. Most importantly, calories do count!
Naude CE, Schoonees A, Senekal M, Young T, Garner P, Volmink J. Low Carbohydrate versus Isoenergetic Balanced Diets for Reducing Weight and Cardiovascular Risk: A Systematic Review and Meta-Analysis. PLoS One. 2014 Jul 9;9(7):e100652
Johnston CS, Tjonn SL, Swan PD, White A, Hutchins H, Sears B. Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets. Am J Clin Nutr. 2006 May;83(5):1055-61
Soenen S, Bonomi AG, Lemmens SG, Scholte J, Thijssen MA, van Berkum F, Westerterp-Plantenga MS. Relatively high-protein or ‘low-carb’ energy-restricted diets for body weight loss and body weight maintenance? Physiol Behav. 2012 Oct 10;107(3):374-80