Rethinking Obesity

BY DEREK LOWE 

Like many people, I have a shelf that has several of my old high school and college yearbooks on it. The faces and scenes they depict are receding farther back in time, damn it all, and as they do they take on interesting aspects that you couldn't have predicted at the time. In my case, the high school ones are from the late 1970s and the college ones are correspondingly from the early 1980s. The hairstyles and the clothing therein have over the years cycled in and out of looking (alternately) odd and old-fashioned or weirdly contemporary, as these things do. Just about any electronic device looks bizarre, of course, and more bizarre by the year - it's the same feeling of watching someone in an old sitcom episode pick up a portable telephone the size of an uncut loaf of bread. 

But you know what looks strange, to the point of being unable to not notice it once you've seen it? How thin almost everyone is. I don't (necessarily) mean by comparison to their later selves, but just in general. And it's not just because these are pictures of high school and college students, because (1) people of those ages definitely aren't as thin as that now and (2) the same observation applies to the photos of the faculty and staff. Looking at these pictures, you inescapably have to admit that people have gotten bulkier over the years, in every category. The numbers bear this out, of course. Sixty years ago, the estimate is that just under 15% of the US population had a BMI over 30, and now it's more like 40%. A lot of those gains have come since the early 1980s, and one rather startling statistic is that the least obese state now (Colorado) would have been the most obese state with those same numbers in 1980, and by a wide margin. Similar trends are obvious in many other countries around the world.

Opinions on how and why this has happened are easily obtained. But I wanted to highlight what is sure to be a controversial proposal that's just come out recently. If there's one thing that people can agree on about weight gain, it's that it happens when people consume more calories than they expend. But as Gary Taubes notes in that commentary, that's not a very useful explanation. You wouldn't get very far if you applied that same level of reductionism to personal finance: the way to get rich is obviously to spend less money than you take in, but there are some key details lacking in that approach. Getting rich is better approached by studying the many ways that one can accumulate excess money, rather than looking at "money imbalance" by itself, and obesity may well be better approached by thinking of it as a disorder of fat accumulation, rather than just as an illustration of calorie imbalance.

Coming at the problem from this direction feels strange at first, because we've all been used to thinking in energy-balance terms for decades - and frankly, we've all been used to thinking of this as largely a behavioral problem as well (willpower, depression, and all that). But as Taubes details, this used to be a very prominent view in the field decades ago, and it was not abandoned because it was disproven. Indeed, a close look at what we now know about human obesity and animal models of it suggests that this is still a valuable approach. Fat mobilization, patterns of fat deposition, the metabolic effects of fat deposits once they accumulate (it's far from a passive store) - all of these point to a "fat storage disorder".

Here's a new review (open access) of the proposed mechanism. In short, eating a high-glycemic-load diet (rich in easily metabolized carbohydrates) deranges the insulin signaling axis towards glucose uptake, lipogenesis, and fat storage. It's not just the calorie content; there are consequences to the fat storage that get worse over time. Instead of a positive calorie balance gradually increasing fat deposition, this is more the opposite: fat deposition (caused by high glycemic foods) drives a positive energy balance. The solution would be to avoid diet rich in high glycemic foods, favoring one whose calories come more from proteins and oils.

This has been a longstanding argument in human nutrition, and one good thing about that review is that it lists the evidence for and against this idea, along with the various attempts to prove or disprove it in human studies and animal models. In the end, the authors say that dogmatic statements about which approach to human obesity have been proven simply cannot be supported by the evidence: we need more data, and better-designed studies, and we definitely need to stop assuming that we already know what the answer is. That's not going to be easy. You see this in any field - people get invested in a given framework and are not happy about having to treat it as it were back to being a matter for speculation again. That investment is partly psychological, partly in career capital and reputation, and partly literal investment as in money and assets. The authors:

The field of obesity should embrace paradigm clash as an essential step forward. Toward this end, investigators should, first, refrain from hyperbolic claims to have disproven (or proven) alternative explanations of the obesity pandemic; second, clarify the Energy Balance Model, specifying contrasting causal and testable hypotheses; third, form collaborations among scientists with diverse viewpoints to test predictions in rigorous and unbiased research; and fourth, to facilitate these aims, depersonalize the debate, scrupulously avoiding ad hominem argument. Rigorous research using complementary designs will be needed to resolve the debate, clarify a middle ground, or point the way to new explanatory models that better encompass the evidence.

Hard to argue with that. We clearly are getting something wrong - and as evidence, I present the Harrisburg High School 1979 yearbook.

https://www.science.org/content/blog-post/rethinking-obesity