May 22, 2011

The Truth About Fructose

Fructose is a simple sugar (a monosaccharide, in technical terms) that has been the subject of a great deal of recent nutritional controversy. Alarmist websites, Youtube videos, and even some peer-reviewed research papers have railed against the consumption of fructose, linking it with obesity and the onset of disease. A popular “health guru” has gone as far to call it the “worst of the worst,” and has suggested that fruit intake be severely curtailed (fructose is found in fruit). Are these claims warranted?

To help clear up the confusion, I consulted with nutrition expert James Krieger. I’ve known James for about a decade, and have found him to be one of the most astute fitness pros around (you might remember that I wrote a post overviewing his meta-analysis about Single vs. Multiple Sets). Here he sets the record straight on what is often a misunderstood topic. I’m sure you’ll find his comments of great interest.

BJS: Thanks for agreeing to do this interview, James. Let’s first start off by telling us about your background.

JK: I am the founder of Weightology, LLC, a website dedicated to providing honest, accurate, evidence-based information on weight management. I have a Master’s degree in nutrition from the University of Florida, and a second Master’s degree in Exercise Science from Washington State University. I am the former research director for a corporate weight management program that treated over 400 people per year, with an average weight loss of 40 pounds in 3 months. My research papers have been published in journals such as the American Journal of Clinical Nutrition and the Journal of Applied Physiology. I am also the editor of Journal of Pure Power, an online magazine that delivers scientific information on training and nutrition to athletes and coaches.

BJS: Fructose consumption is a controversial subject these days. How does fructose differ from other simple sugars?

JK: Fructose is much sweeter than other sugars. There are also differences in the way your body metabolizes fructose compared to other sugars. Fructose doesn’t go straight to your bloodstream; instead, it is metabolized by the liver first. The liver can take the fructose, convert it to glucose, and then release that glucose into the blood. It can also take that fructose and store it as glycogen. Finally, it can convert the fructose to fat. It is this conversion to fat that causes a lot of confusion and alarmism.

BJS: There are studies showing that fructose can have a detrimental effect on various markers of health. What’s your take on this?

JK: There certainly are studies showing that fructose can have this detrimental effect. However, these studies have used extremely high doses of fructose. Unfortunately, people have taken this information to the extreme and have concluded that, since high amounts of fructose can be a problem, then any fructose must be a problem. This is simply not the case.

Do we consume too much fructose in our society? Certainly, but we consume too much of everything else too. It is a mistake to try to point the finger at one thing. Anything consumed in excess can be problematic.

BJS: What about the theory that fructose has a greater propensity to be converted into body fat?

JK: This theory unfortunately takes fructose metabolism out of context, and fails to address the bigger picture. People think this because fructose bypasses an important enzyme in the liver, and thus think it is easier to convert the fructose to fat. The problem with this line of thinking is that it fails to address the fact that fructose metabolism changes depending upon the energy state of the body. If you are in an energy deficit, the fructose will not have a greater propensity to be converted to body fat. Rather, it will be directed towards storage as glycogen, or conversion to glucose for energy.

The other problem with this line of thinking is people confuse triglycerides with body fat. If fructose is converted to fat in the liver, it doesn’t mean the fat ends up as body fat. In fact, there is some evidence that fructose is less likely to be converted to body fat. We also have to remember that any fat formed from fructose in the liver can be burned and used for energy. Again, we have to look at the big picture.

BJS: Fruits contain fructose. Should people limit their intake of fruits if they want to lose weight?

JK: As long as you are in an energy deficit, you will lose weight. It doesn’t matter how much fructose you consume. There is no valid scientific reason to limit intake of fruit. Fruit can actually be very beneficial for weight loss because of its fiber content, which makes you feel fuller. It is also low in energy density, and there is a lot of research showing that eating foods that are low in energy density helps promote weight loss.

In the weight management program that I did research for, our clients started the program on high protein shakes sweetened with fructose, and mixed with berries. Our clients were getting a lot of fructose in the diet from the combination of shakes and berries. Yet, they lost tremendous amounts of weight.

BJS: High fructose corn syrup (HFCS) is used in many food products. Is HFCS worse for you than sugar?

JK: There is little difference in the composition of sugar and high fructose corn syrup. Both contain similar amounts of fructose. The only reason manufacturers choose HFCS over regular sugar is because HFCS is cheaper.

When you look at all of the studies that compare sucrose (table sugar) metabolism to HFCS metabolism, they are identical as far as your body is concerned.

BJS: How do you explain the studies showing that obesity rates skyrocketed after the introduction of HFCS?

JK: This research suffers from a fallacy known as post hoc, ergo propter hoc (after this, therefore because of this). Just because event B happens after event A, doesn’t mean event A caused event B. Obesity also skyrocketed after the introduction of microwave ovens and VCR’s, but that doesn’t mean microwave ovens and VCR’s cause obesity!

BJS: What about the fact that HFCS isn’t “natural.” Should this matter?

JK: There is no evidence that products that are “natural” are any healthier or safer than products that are not “natural.” For example, there are many natural substances out there that are poisonous or carcinogenic to the human body. Calamus oil, which was a natural food additive before it was banned in 1968, is a carcinogen.

In fact, I often ask people to define what they mean by “natural” and they struggle to do so. If you think about it, there is really no clear cut way to determine what is natural or artificial. For example, aspartame is actually made up of natural ingredients (aspartic acid, phenylalanine, and methanol). So why would we call aspartame artificial? Also, we call Stevia natural, but that doesn’t make sense because it requires human intervention to extract it from the stevia herb.

BJS: Anything else you’d like to add on the topic?

JK: I would say that people do not need to worry about moderate fructose consumption. Basically, the idea of “everything in moderation” applies to fructose just like anything else. Thanks for the opportunity to interview!

Check out James’ website at:

Check out the Journal of Pure Power at: Journal of Pure Power


  1. Great interview guys! James you’re a smart dude.

    Comment by Bret Contreras — May 22, 2011 @ 6:28 pm

  2. Thanks Bret. You’re right, James is a smart dude 🙂

    Comment by Brad — May 22, 2011 @ 11:19 pm

  3. GREAT article. I wish I would have had this a few hours ago as I just out of a long fructose debate on a forum and would have liked to have shared this. Thanks guys!

    Comment by Mark Fisher — May 22, 2011 @ 11:48 pm

  4. Thanks Brad, for the interview. Solid stuff from Krieger.

    Comment by Chi L. Chiu — May 23, 2011 @ 7:54 am

  5. Good interview. A few questions though.

    1). Given the apparent propensity for fructose to lead to triglyceride formation, if one is in a caloric surplus and trying to gain lean body mass, should moderating fructose intake be a potential factor? For instance, if I could choose to drink 1L of coke after a workout and grab ~60g of fructose and 50g of glucose [roughly], versus 110g of CHO from white rice or something that is otherwise not nutrient dense, would there be a difference in body comp over the short and / or long term? I would suggest yes, at the very least anecdotally, but am interested in evidence either way.

    2). Similarly, if one is exercising and/or weight controlling to prevent or reduce heart disease risk factors, would one want to moderate or modulate fructose intake regarding triglyceride formation again?

    Thanks for the evidence based information

    Comment by Dan — May 23, 2011 @ 9:14 am

  6. The Truth About Fructose…

    An interview with James Krieger. This man knows his stuff, must read….

    Trackback by FitMarker — May 23, 2011 @ 2:16 pm

  7. Good stuff guys. I agree that in HEALTHLY people in MODERATION, there is not much to worry about.

    Like all things, the “state” of the person needs to be factored in. A type 2 diabetic is not going to do well with fructose since they have issues with carb metabolism. People tend to jump to a healthy population and state the same thing (fructose = bad).

    Ideally, you want to be as metabolically flexible to as many different fuel sources as possible. This includes evil fructose too! 😉

    While high amounts of isolated sugar doesn’t come with beneficial compounds for health, they should not destroy you either in moderation. At best, they should be neutral (again, in a healthy person who can use carbs for fuel).

    I am amazed that people can use a large 7-11 Slurpee without ice at all! If I put the wrong fuel in my car, I will barely make it around the block!

    Good work
    Rock on
    Mike T Nelson PhD(c)

    Comment by Mike T Nelson — May 23, 2011 @ 3:51 pm

  8. Great work guys. I’ll be saving this one and referring back to it when fructose debates come up with my clients/friends, and other on-line “gurus.”


    Comment by Danny McLarty — May 24, 2011 @ 12:32 am

  9. Excellent interview! Hit the nail right on the head.

    Comment by Mark Young — May 24, 2011 @ 12:00 pm

  10. As much as I enjoy your observations across a broad range of health
    matters I must take you to task re: ‘The Truth About Fructose’ and
    your attempt to, “clear up the confusion” by relying totally on the
    opinion of one nutrition expert, James Krieger.

    Questions surrounding the increasing use of Fructose and its impact
    on consumers are, in fact, far from being answered! Reading your
    piece I believed that you slanted the subject matter by allowing not
    only your own views to influence the blog (see opening para.), but
    that also by relying totally on Krieger’s opinion you provided
    readers with a simplistic and dismissive overview – (“JK: I would say
    that people do not need to worry about moderate fructose
    consumption”) of an important health subject that is of increasing

    I’m sure you understand that by contributing to any discourse,
    controversial or not, you inevitably open yourself up to criticism
    and consequently, it’s often more enlightening, unless your
    background warrants a defining position, to play devils advocate.
    Might I therefore, refer you to a recently published paper that I
    hope will encourage a somewhat more balanced viewpoint:

    Comment by Michael — May 24, 2011 @ 4:51 pm

  11. Hi Dan:

    A combination of glucose and fructose is beneficial post-workout. In addition to promoting an insulin response which has important anabolic and anti-catabolic properties in the post-workout period, glucose is the primary source of muscle glycogen. Fructose, on the other hand, preferentially replenishes liver glycogen (glucose is of limited utility to the liver, a phenomenon called the “glucose paradox”). Thus, the two types of sugar work synergistically to restock the body’s glycogen stores. Personally, I’d advise using a natural fruit juice rather than soda–you at least get the benefit of greater nutrient density.

    As for the metabolic consequences of fructose consumption for those trying to prevent heart disease, there certainly is a good deal of evidence showing a negative effect of high fructose consumption. But from the studies I’ve seen, moderate consumption (< ~100 grams a day) does not pose negative effects. People do respond differently to various macronutrients, though, so that would be something to evaluate with your physician after getting a lipid profile. Brad

    Comment by Brad — May 25, 2011 @ 7:12 am

  12. Hi Mike:

    I’m certainly not a fan of soda or other processed, empty calorie foods (see my post on why we should have a soda tax). Personally, I almost never indulge in these types of foods. When you abstain from such foods, you lose the craving for them (as I have), and this is only a good thing.

    That said, the point of this post was to provide some balance to the argument being made by some of the alarmists that pervade the internet. Some have even gone as far to say fruit–which has so many terrific health benefits–should be limited to one piece a day. I think James did an excellent job providing evidence-based info on a controversial topic.


    Comment by Brad — May 25, 2011 @ 7:19 am

  13. Michael:

    I appreciate your comments. I really don’t see where the issue is “slanted” here. James has a better grasp on fructose research than anyone I know, so I allowed him the opportunity to present his educated views on the topic. As I see it, my job as interviewer is to ask probing questions and let the interviewee answer the questions. I allow unfiltered comments to my blog, so if people disagree (as you apparently do), they can chime in and start a discussion. This is how people learn.

    I did look over the review you provided by Wiernsperger et al. (2010). IMO, the article actually supports James’ statements. To quote from pg. 735: “In humans, the deleterious effects seen with 20-25% fructose as an energy source were not observed when more realistic quantities of 4-12% fructose were investigated.” This is in line with James’ opinion that people don’t need to worry about moderate fructose consumption.

    Even in diabetic patients, moderate fructose consumption does not seem to have negative effects on markers of health. For example, Osei et al. (1987) found that consumption of 60 grams of fructose a day did not cause any disturbance in glucose homeostasis or lipid parameters in a group of diabetic subjects over a 12 week period. Similarly, Anderson et al. (1989) found that diabetics who consumed a 50–60 grams a day of fructose did not negatively affect plasma glucose, insulin, or lipid concentrations. The researchers went on to conclude that “If total calorie intake is controlled to promote desirable body weight, crystalline fructose used with a high-carbohydrate high-fiber low-fat diet appears to be safe and acceptable for diabetic individuals.”

    If you have research that specifically refutes any of the points James made, I would be interested in seeing it. As someone who subscribes to the scientific method, I am always willing to change my opinion if evidence warrants.

    Again, thanks for stimulating discussion on the topic.


    1) Osei K, Falko J, Bossetti BM, Holland GC. Metabolic effects of fructose as a natural sweetener in the physiologic meals of ambulatory obese patients with type II diabetes. Am J Med. 1987;83:249–55

    2) Anderson JW, Story LJ, Zettwoch NC, Gustafson NJ, Jefferson BS. Metabolic effects of fructose supplementation in diabetic individuals. Diabetes Care. 1989;12:337–44

    Comment by Brad — May 25, 2011 @ 7:45 am

  14. I was going to address some of the comments made here but looks like Brad already adequately addressed them.

    Thank you all for your interest in this article, and thank you Brad for interviewing me!

    Comment by James Krieger — May 27, 2011 @ 1:32 pm

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