Athena, Holding Your Hair, Whispering In Your Ear

For me a few are enough, one is enough, none is enough. This is not for the many, but for you. We are audience enough for each other.

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A wide-ranging survey of the science underlying human obesity and appetite, with a particular focus on neuroscience. The author is a scientist by training, and it shows: he routinely gets down into granular details of the science. But he's also a strong writer and organizes the discussion thematically, which makes for a surprisingly readable book. The book effectively harmonizes and explains the voluminous scientific literature for a lay reader, and the effect is wonderfully reminiscent of Daniel Kahneman's magisterial Thinking Fast and Slow (which Guyenet clearly admires).

Perhaps the best feature of the book is that the author takes the available data seriously and tries to reconcile the various strands of the science that might, at first glance, seem contradictory. What is more remarkable is that his theory manages to provide unified and coherent (if provisional) answers to some vexing open questions.

At a high level, Guyenet's theory is that modern food environments contain hyper-palatable "high reward" foods in an absurdly high variety, and that this food environment effectively fools or actually damages our bodies' fat regulation system (called the lipostat) such that those of us genetically susceptible to it will gain weight and defend higher setpoints no matter what we consciously intend to do.

While that may sound superficially similar to some common narratives percolating through the public conversation about obesity, it is crucially different in several key respects.

One example that has puzzled me for years: there are studies suggesting that variance in weight is to a large extent (70%) genetic. However, in 1905 only 5% of the population was obese, whereas now upwards of one third of the population is obese. How can obesity be predominantly genetic, when the demographics are changing that drastically over three or four generations in the same population? The answer (according to Guyenet) is that our dietary variety and access to hyper-palatable food have changed, and it is not weight that is largely genetic, but rather one's susceptibility to gaining weight from this new food environment. He supports this theory not only with scientific studies, but also with observations of modern hunter/gatherer societies who exhibit very low obesity even in situations of caloric surplus, until they come into contact with Post-Industrial high variety food environments.

Similarly, I've always wondered how it is that various seemingly mutually inconsistent diets can all produce results (i.e. low-carb/keto style diets maintain they work because carbohydrates are the problem, low fat diets maintain they work because fat is the problem, vegan weight loss plans maintain they work because they avoid saturated fat and meat, etc.). The usual answer is that they all ultimately result in calorie restriction, but that's not necessarily true and is, at best, only half an answer. Here, the author suggests that the driver of obesity is dietary variety coupled with "high reward" foods, such as foods that include significant quantities of fat and sugar (a combination that rarely occurs in nature). The reason all these divergent diets "work" is that they all exclude some number of major "reward factors" and reduce variety, which results in people floating to a somewhat lower setpoint. Again the author works through the supporting studies, including studies where people provided with only bland, but nutritionally complete, food eat less and lose weight without being instructed to do so and without experiencing hunger. Additionally he dives deep into animal studies, which, while not necessarily generalizable to people, are immensely fascinating too.

Helpfully, the author also offers concrete suggestions on how to manage obesity based on the available science. In that vein, he provides some of the usual lifestyle suggestions (improving sleep, exercising, etc.), which should be familiar to anyone following the obesity conversation. But his dietary suggestions are heterodox: instead of focusing on portion control, he recommends primarily eating bland foods with specific characteristics (high fiber, high protein, low added sugar, low salt, etc.), reducing exposure to high reward foods (don't buy them or keep them out where you can see them, etc.), and trying to eat fewer different kinds of food at each meal.

If the idea that you can eat all you please so long as its bland sounds like a fairy tale, let me offer a personal anecdote. A few years ago I started eating the same "bland" breakfast (oats and milk) and lunch (beans and brown rice) most days for medical and personal reasons. I kept eating whatever I pleased for supper.

My medical issues improved, but I also wound up losing quite a bit of weight. Notably, I didn't feel hungry or consciously try to limit how much I ate, and I sometimes didn't even want to finish my lunch. I had been a little confused about the sheer quantity of the weight loss. At first, I chalked it up to the fact that I was exercising more, but, since the pandemic has forced me out of the gym, my exercise volume has gone down a fair bit. In that time my weight has only gone lower, and I'm currently at my lowest adult weight.

After reading this book, the mystery seems much less mysterious: this outcome is exactly what one would expect based on the author's theory. Returning to the non-obese hunter/gathers I mentioned above, the author notes that, in one such society, people get the majority of their calories from just two or three bland foods. I appear to have inadvertently approximated that situation for myself. If someone had told me fifteen years ago that I could manage my weight (and improve other health outcomes) without conscious effort by eating bland, easy to make, cheap food two-thirds of the time, I'd have taken that bargain and never looked back.

Of course anecdotes are not data, and thankfully Guyenet presents some pretty compelling studies in support of his theory. If you remain skeptical (and you should!), the book itself offers a much more convincing presentation.¹ I highly recommended this book for anyone who wants a view into the current medical understanding of the mechanics of weight gain and loss. For those seeking lifestyle advice it may also be a fruitful read, but I'll note that the last chapter provides a nice succinct set of steps for applying the conclusions to one's own life. An impatient reader looking only for action items can profitably skip to the end.