So what does cause this fattening effect? I think the book’s answer is “no single factor, but that doesn’t matter, because capitalism is an optimization process that designs foods to be as rewarding as possible, so however many different factors there are, every single one of them will be present in your bag of Doritos”. But to be more scientific about it, the specific things involved are some combination of sweet/salty/umami tastes, certain ratios of fat and sugar, and reinforced preferences for certain flavors.
Modern food isn’t just unusually rewarding, it’s also unusually bad at making us full. The brain has some pretty sophisticated mechanisms to determine when we’ve eaten enough; these usually involve estimating food’s calorie load from its mass and fiber level. But modern food is calorically dense – it contains many more calories than predicted per unit mass – and fiber-poor. This fools the brain into thinking that we’re eating less than we really are, and shuts down the system that would normally make us feel full once we’ve had enough. Simultaneously, the extremely high level of food reward tricks the brain into thinking that this food is especially nutritionally valuable and that it should relax its normal constraints.
Adding to all of this is the so-called “buffet effect”, where people will eat more calories from a variety of foods presented together than they would from any single food alone. My mother likes to talk about her “extra dessert stomach”, ie the thing where you can gorge yourself on a burger and fries until you’re totally full and couldn’t eat another bite – but then mysteriously find room for an ice cream sundae afterwards. This is apparently a real thing that’s been confirmed in scientific experiments, and a major difference between us and our ancestors. The !Kung Bushmen, everyone’s go-to example of an all-natural hunter-gatherer tribe, apparently get 50% of their calories from a single food, the mongongo nut, and another 40% from meat. Meanwhile, we design our meals to include as many unlike foods as possible – for example, a burger with fries, soda, and a milkshake for dessert. This once again causes the brain to relax its usual strict constraints on appetite and let us eat more than we should.
The book sums all of these things up into the idea of “food reward” making some foods “hyperpalatable” and “seducing” the reward mechanism in order to produce a sort of “food addiction” that leads to “cravings”, the “obesity epidemic”, and a profusion of “scare quotes”.
Scott Alexander, “Book Review: The Hungry Brain”, Slate Star Codex, 2017-04-27.
May 4, 2019
QotD: Calorie-dense modern snack food
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