Carbs and insulin vs. reward theory as the cause of obesity


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For those interested in the cause of obesity, a lengthy post by blogger and neurobiologist Stephan Guyenet is rocketing around the Internet. After a rather testy exchange with Gary Taubes at the Ancestral Health Symposium (which culminated with Taubes offering Guyenet this no-so-friendly advice: “I would just recommend in the future you should pay attention to populations that might refute your hypothesis rather than just presenting populations that support.  That’s always key in science.“), Guyenet decided to write a detailed dissection of Taubes’s carbohydrate theory of obesity, explaining why it’s “not only incorrect on a number of levels, but may even be backward.”

Here’s Taubes’s own statement of the theory in question, as quoted by Guyenet from Good Calories, Bad Calories:

This alternative hypothesis of obesity constitutes three distinct propositions.  First, as I’ve said, is the basic proposition that obesity is caused by a regulatory defect in fat metabolism, and so a defect in the distribution of energy rather than an imbalance of energy intake and expenditure.  The second is that insulin plays a primary role in this fattening process, and the compensatory behaviors of hunger and lethargy.  The third is that carbohydrates, and particularly refined carbohydrates– and perhaps the fructose content as well, and thus perhaps the amount of sugars consumed– are the prime suspects in the chronic elevation of insulin; hence, they are the ultimate cause of common obesity.

Guyenet’s post is an interesting read, and it certainly raises some questions about Taubes’s reductionist approach to obesity (which I’ve criticized in previous posts). It should be noted that Guyenet himself has a Grand Theory of Obesity, which he dubs the “food reward” theory. It basically argues that modern foods trigger reward behaviour in our brains without the accompanying satiety signals that traditional foods would offer. To his credit, he’s more circumspect about trumpeting the powers of his theory: the post I linked to is titled “Food Reward: a Dominant Factor in Obesity.” No doubt that Taubes would have said “the Dominant Factor…” 🙂

Still, my overriding sense is that scientists (and journalists, for that matter) with Grand Theories rapidly become unable to critically evaluate data that conflicts with their theory. Personally, I think it’s highly unlikely that we’ll find a single dominant factor that explains the dramatic rise in obesity over the last few decades, and the endless search for that one magic bullet distracts us from the obvious contributing factors that we already know about.

10 Replies to “Carbs and insulin vs. reward theory as the cause of obesity”

  1. No doubt, the several books written by Taubes highlighting his specific theory of obesity make it very difficult for him to radically change his position.

  2. If we find that carbs (especially refined carbs) have an inherently higher food-reward value, then Taubes and Guyenet can both be right.

  3. Is it really that difficult?…

    My Not-So-Grand-Theory:
    1. People like food (and are likely programmed to eat a lot of food when it is available).
    2. People don’t like negative peer pressure.
    Nowadays, so much food is available for cheap all the time that people eat far more calories than they use. This has been true for awhile but it took some time until being fat was socially acceptable in the west. Note that in some countries where it has been socially acceptable to be obese for longer than it has been in the west, and in fact a sign of wealth (e.g. – India), obesity has been a problem with the wealthy for a long time.

    I’m not saying that some details of many scientists’ explanations for obesity are not true, but they probably only cause small variations. For the average person, what is acceptable socially is likely the driving factor. Most people’s mindset would be that they only restrict themselves if they feel pressure to do so, and for most people, long term health does not seem to be enough pressure.

  4. I don’t think you are doing Guyenet justice here. He specifically states that he doesn’t think reward can account for all obesity – he really is just proposing it as *a* dominant mechanism? Given that, what exactly would distinguish a “Grand Theory” that claims to explain only many cases from a plain theory that claims to explain many cases? I don’t think you can say; the reason is that no such distinction exists.

  5. Does there really have to be one grand theory? Could it be that we just eat too much, too much of what we eat is junk (including refined carbs), we aren’t active enough (not just exercise, but daily activity), we like to reward ourselves, there is genetic variation among individuals in predisposition to obesity, food sensitivities, and so on… I’m no obesity expert, but it seems to me that it’s got to be multifactorial, and specific factors may vary on an individual level.

  6. You’re definitely not doing Guyenet justice. He makes clear he is not proposing a grand theory. He presents food reward as a reason why some people gain weight among countless other factors.

  7. @Pete Larson
    I think most anyone without a horse in the race – or a book on the shelves – would probably agree with you. Unfortunately, granting that the obesity epidemic is multifaceted also means that we can’t propose one simple solution. And while the issue is certainly complex, simplicity sells.

  8. Thanks for the comments, folks. @Pete (and @Alex): that’s pretty much what I think too.

    @Phil and @Abby: You may be right that I’m not doing Guyenet justice. I’ve only read parts of his blog, so perhaps my grasp of his ideas isn’t very deep. Certainly, I agree that it’s a big plus that (unlike Taubes) he doesn’t see his theory as the one and only factor in obesity. That being said, I think it’s not just semantics to see a difference between a “dominant factor” and a “factor”! 🙂

  9. @alex
    I think some of the comments here don’t give enough credit to the information to be learned by doing science to try to understand why people get fat.

    What Taubes and Guyenet and many others agree on, I believe, is that the common wisdom has it backwards: we don’t get fat because we eat too much, instead we eat too much (and/or have a lowered metabolism) because our bodies want us to get fat(ter).

    Our bodies have a fat regulation mechanism, and in some populations, like that of the U.S. in general, it seems to have broken down in many people leading to common obesity. In other populations, even those with similar social mores and food availability, many fewer people are obese.

    Why? And can you prove your theory it by doing controlled studies of how the biochemistry works in people? Or whether changing diet in accordance with your theory will reverse the breakdown of the fat regulator?

    Taubes says carbohydrates, or sometimes processed carbohydrates, are the mechanism which breaks fat regulation. Guyenet agrees that processed food seems to be a cause, but disagrees on the mechanism: as I understand it, he and many other scientists studying this problem believe the fat regulator in the brain is broken by food combining high calories and food reward (Guyenet also believes industrial food production takes advantage of this weakness to sell).

    Guyenet’s rebuttal to Taubes is trying to show that the science currently better supports the food reward hypothesis.

  10. I really don’t get all the hullabulloo, but especially the backlash against Taubes. I read Taubes’s book, implemented the idea, and lost 13 pounds, as have countless others. So why is he wrong?

    Also, I’ve never heard Taubes say his carb theory is the only worthy one and the sole reason for obesity. Maybe he’s been strongly worded in personal appearances. But he states in the beginning of his book that he’s merely a journalist who bothered to go through the history of all of this. Anyone in this obesity fight should be able to see that it’s multi-factorial.

    The two main points I got from Taubes were that a calorie is not a calorie is not a calorie. It does matter where those calories come from, and this has certainly been borne out by my experience. I know that this is anecdotal, but I was not an overeater of SAD foods and Guyenet’s food reward didn’t seem to apply to me. Now that I’m Primal…he might have an argument. 🙂

    The other Taubesian idea is that getting fat is about our bodies fulfilling a sort of programmed destiny. I was in the beginning stages of this ramp-up, and as an athletic 30-something, I was getting extremely dismayed that my 5-day-a-week workouts weren’t making a difference. And thanks to Taubes, I know why. It wasn’t my fault, and I had to get my food intake in order.

    It seems to me that the crux of their disagreement has to do with population studies. And I think these studies are important and enlightening, but we shouldn’t necessarily extrapolate that data for our own lives. I am not interested in an Inuit diet, no matter how healthy they were before SAD invaded. Of course there are populations that existed on more carbs and yadda yadda yadda, but what are we dealing with now on the ground? So people ate many different diets and thrived, so what? Isn’t the same true now? And after all this infighting and side-taking aren’t we all just eating real food anyway?

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