I first learned about [Stephan] Guyenet’s work from his various debates with Gary Taubes and his supporters, where he usually represents the “establishment” side. He is very careful to emphasize that the establishment doesn’t look anything like Taubes’ caricature of it. The establishment doesn’t believe that obesity is just about weak-willed people voluntarily choosing to eat too much, or that obese people would get thin if they just tried diet and exercise, or that all calories are the same. He writes
The [calories in, calories out or CICO] model is the idea that our body weight is determined by voluntary decisions about how much we eat and move, and in order to control our body weight, all we need is a little advice about how many calories to eat and burn, and a little willpower. The primary defining feature of this model is that it assumes that food intake and body fatness are not regulated. This model seems to exist mostly to make lean people feel smug, since it attributes their leanness entirely to wise voluntary decisions and a strong character. I think at this point, few people in the research world believe the CICO model.
[Debate opponent Dr. David] Ludwig and I both agree that it provides a poor fit for the evidence. As an alternative, Ludwig proposes the insulin model, which states that the primary cause of obesity is excessive insulin action on fat cells, which in turn is caused principally by rapidly-digesting carbohydrate. According to this model, too much insulin reduces blood levels of glucose and fatty acids (the two primary circulating metabolic fuels), simultaneously leading to hunger, fatigue, and fat gain. Overeating is caused by a kind of “internal starvation”. There are other versions of the insulin model, but this is the one advocated by Ludwig (and Taubes), so it will be my focus.
But there’s a third model, not mentioned by Ludwig or Taubes, which is the one that predominates in my field. It acknowledges the fact that body weight is regulated, but the regulation happens in the brain, in response to signals from the body that indicate its energy status. Chief among these signals is the hormone leptin, but many others play a role (insulin, ghrelin, glucagon, CCK, GLP-1, glucose, amino acids, etc.)
The Hungry Brain is part of Guyenet’s attempt to explain this third model, and it basically succeeds. But like many “third way” style proposals, it leaves a lot of ambiguity. With CICO, at least you know where you stand – confident that everything is based on willpower and that you can ignore biology completely. And again, with Taubes, you know where you stand – confident that willpower is useless and that low-carb diets will solve everything. The Hungry Brain is a little more complicated, a little harder to get a read on, and at times pretty wishy-washy.
But listening to people’s confidently-asserted simple and elegant ideas was how we got into this mess, so whatever, let’s keep reading.
Scott Alexander, “Book Review: The Hungry Brain“, Slate Star Codex, 2017-04-27.
May 31, 2019
QotD: How we gain weight
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