Why the brain matters in obesity
Those of you interested in nutrition may already be following the online debate between Gary Taubes and Stephan Guyenet — back in August, Guyenet critiqued Taubes’s carbohydrate-insulin hypothesis, and now Taubes is returning the favour by critiquing Guyenet’s food-reward hypothesis. I’m not going to get into the nitty-gritty of the debate here, except to say that I think it’s a mistake to frame this debate as an “either-or.” Despite Taubes’s insistence to the contrary, the two ideas can coexist — and even if they do, I suspect they still don’t add up to the “whole truth” about obesity. Here’s one reason why.
In one of his recent posts, Taubes makes the distinction between body-centred and brain-centred theories of obesity (or you can think of it as physiology vs. psychology, one of his commenters points out). Taubes believes obesity originates in the body:
In this paradigm, specific foods are fattening because they induce metabolic and hormonal responses in the body — in the periphery, as its known in the lingo — that in turn induce fat cells to accumulate fat. The brain has little say in the matter.
Leaving aside the precise mechanism, I largely agree with the idea that regulation of calories in and calories out isn’t under the conscious control of the brain. And I’m pretty sure Guyenet would agree too. But I’m not quite ready to conclude that the brain plays no role.
This is a figure from a study published in the Archives of Pediatrics & Adolescent Medicine in 2009, from researchers at Penn State (no wisecracks please). The text is freely available here. The study followed 1,061 children, who were tested at the age of 3 for self-control (the length of time they were able to refrain from playing with a fun toy after being asked not to) and then again at the age of 5 for delayed gratification (the classic Marshmallow Test, which I’ve written about before, except using M&Ms, animal crackers or pretzels: they could have a small amount anytime, or a larger amount if they waited 3.5 minutes). Then their BMI was tracked until their turned 12.
The results are pretty clear: doing well on either or both of the impulse-control tests predicts less weight gain nine years later. So the question is: how can a test that involves (not) playing with a toy when you’re 3 years old predict future weight gain, if the brain has no say in weight gain?
Let me be absolutely clear: I don’t think “better impulse control” will play any useful role in weight loss for the vast majority of people. Once you’re overweight, I suspect physiology totally swamps psychology in most cases. But if you’re looking for an overall understanding of the mechanisms of weight gain and loss — and if, like Taubes, you insist that the correctness of your theory means that all alternate ideas must be 100% incorrect — then I believe you can’t ignore the brain (and its interactions with the modern food/physical activity environment) completely.