A popular theory among fitness professionals is that taking short rest periods between sets maximizes muscular growth. The theory is primarily based on the hormone hypothesis, whereby limiting inter-set rest promotes greater elevations in post-exercise growth hormone, IFG-1 and testosteron...
December 7, 2013
I’m happy to report that the meta-analysis on protein timing that I co-authored with Alan Aragon and James Krieger has been published in the Journal of the International Society of Sports Nutrition. The study has created quite a stir, provoking discussion and debate in numerous forums. As a testament to its impact, the study already is in the top five most viewed articles for the JISSN over the past year at the time of this writing — less than a week after its publication!
This post will recap the study and provide consumer-friendly practical application of results. Before getting into particulars, however, here is a brief overview as to how it all came about.
A Little Background
For many years I was a staunch proponent of the concept of an “anabolic window of opportunity,” advocating that protein and carbs needed to be consumed within about an hour post-workout to maximize the hypertrophic response to an exercise bout. I’d read the seminal text by Poortman and Ivy that championed the approach. I’d seen numerous studies suggesting the presence of a narrow window, including the JISSN position stand on the topic. I’d heard a number or prominent researchers in the field lecture at conferences on the importance of quickly ingesting nutrients after resistance training for promoting anabolism. The evidence seemed pretty overwhelming – a no-brainer.
A couple of years ago, I asked my good friend and colleague Alan Aragon – one of the preeminent sports nutritionists in the world – to review the nutritional chapter for my book, The M.A.X. Muscle Plan. In doing so, Alan challenged my recommendation as to the importance of nutrient timing. He pointed out various flaws in the underlying science. He put forth the hypothesis that the concept was largely overhyped.
I was intrigued.
I did a thorough literature search, combing through all the relevant studies, both acute and long-term. And guess what? The more I looked into the matter, the less convinced I was at the veracity of supporting evidence for a narrow anabolic window. It became evident that the staunch proponents of nutrient were cherry-picking studies to support their position while ignoring conflicting research. Moreover, there were important limitations in many of the studies favoring timing that often were not properly addressed. It was clear to me that a balanced review was needed to provide clarity on the topic.
Over the next several months Alan and I delved in head-first, discussing the body of research in context and developing evidence-based conclusions. This process ultimately led to a change in our perspectives, with both of us moving more to the center (as reflected in our practical recommendations). The final product was titled Nutrient Timing Revisited: is there a post-exercise anabolic window?, published in JISSN earlier this year. It is now by far the most popular article in the history of the journal and has been highly cited in subsequent research.
One thing that really struck me when reviewing the literature was the disparity in longitudinal studies; some showed clear increases in muscular adaptations while others did not. A major issue with long-term training studies is that they have small sample sizes; the time and costs associated with such research limit the number of participants that can be evaluated. It was certainly plausible that studies showing no effect simply lacked the statistical power to note a significant difference (a so-called a Type II error). The only way to evaluate the topic and provide a valid quantitive analysis of findings was to conduct a meta-analysis, where the data from all relevant studies are pooled to achieve optimal statistical power. I spoke with Alan about the undertaking. We contacted nutrition and statistical whiz James Krieger. The rest, as they say, is now history…
Data Collection and Findings
The meta-analysis took several months to complete. We decided on appropriate inclusion/exclusion criteria, coding variables, and other info relevant to the analysis. We were meticulous in our approach, checking and rechecking data for accuracy. Most importantly, we remained unbiased and objective throughout; none of us had any idea what we would find nor did we care. The only thing that mattered was getting clarity on the topic.
It was a very involved process, with an endless number of email exchanges and phone calls. We continually reassessed our methods so that results would properly reflect the body of literature. The most frustrating part was not being able to get any preliminary findings until all coding was complete. Patience was a virtue
The first analysis looked at the basic data. In other words, we did a simple pooled analysis to see if there were any increses in muscle strength or hypertrophy from protein timing. No effects were seen with respect to strength but, lo and behold, there was a small but significant effect on muscle hypertrophy. Had we effectively confirmed the existence of an anabolic window?
Not so fast…
Over the next couple of days we ran sophisticated regression analysis whereby a number of variables (i.e. covariates) were examined independently to evaluate their impact on results. This produced the most interesting finding of all: the quantity of protein explained virtually all the variance in results! Specifically, a majority of studies did not match protein intake between groups: the experimental group consumed substantially more protein than the controls. Thus, the average protein consumption in the control groups were well below what is deemed necessary to maximize protein synthesis associated with resistance training. Only a few studies actually endeavored to match intake. We did a subanalysis of these studies. No effects were found on protein timing (and this was in spite of having to discard a study that showed no effect because of insufficient available data).
Practical Implications and Other Observations
The take home message from the meta-analysis is that there does not appear to be a narrow “anabolic window of opportunity”; for the vast majority of the population it really doesn’t matter whether you consume protein immediately after training or wait for a couple of hours. This should be liberating for most lifters. You don’t have to worry about slamming a shake the minute you finish lifting. It’s okay to relax a bit, do whatever you need to do, and get in your post-workout nutrition when its convenient.
Now the findings of our study come with several caveats. For one, our criteria for timed consumption was < 1 hour pre- or post-workout, while the non-timed groups were > 2 hours. It is not clear if waiting say 5 hours or more after a training session would have a negative impact. In my previous review with Alan, we proposed that a window probably exists, but it is rather wide (4-6 hours) and will depend on when you ate your pre-workout meal. Our findings in this meta-analysis do nothing to change these guidelines.
Another important point is that there is a paucity of studies that have matched protein consumption between the timed vs untimed groups. Although our subanalysis failed to show any differences, statistical power was lacking and it remains possible that there may be an underlying effect that we were not able to detect. We need more well-controlled research where intake is matched between groups.
Finally and importantly, the majority of studies were carried out on untrained subjects; none employed elite bodybuilders or athletes. There are numerous differences between newbies and experienced lifters, including anabolic responsiveness, the ability to train at higher levels of intensity of effort, the capacity to recruit the full spectrum of muscle fibers, etc. These factors may or may not have an impact on the importance of timing. We simply don’t have enough info to make a determination at this juncture. Moreover, the measures used to assess hypertrophy (i.e. DXA, MRI, CT, etc) have inherent limitations and might not be sensitive enough to show small effects that potentially could be meaningful to competitive athletes. So if you are a highly trained lifter where it is essential to achieve absolute maximal hypertrophy, it makes sense to consume protein as quickly as possible post-workout; doing so certainly won’t hurt and possibly might help, albeit to a small extent.
In closing, I want to say special thanks to Dymatize Nutrition for funding this study. They agreed to provide the grant without any strings. They placed no restrictions on findings; whatever we found, we reported. This truly speaks to the integrity of the company. In my book, they are tops when it comes to nutritional supplementation.
In addition, kudos to the JISSN for publishing a study that runs counter to their position statement on the topic. It’s refreshing to see that journals maintain a commitment to science and reaffirms faith in the peer-review process.
One of the important things about meta-analyses and reviews is that they help to guide the direction of future research. Based on our findings, I am in the process of designing a timing study that should help to fill in the gaps in the literature. Still some things to work out, but I hope to get it underway sometime in 2014.
Moreover, Alan, James and I are currently working on a related meta-analysis that should produce equally impactful results. That’s about all I can say at the moment, but will post as soon as data is available. Stay tuned…
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