Book Review: The Hungry Brain

It was joked, of Soviet factories, that if performance were measured by the number of nails produced, they would produce a multitude of nails too small to use; if performance were measured in tonnage, they would produce only one, gigantic nail.

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Capitalism has sort of the opposite problem with food – regardless of what you say you want, capitalism will give you what you crave, for a low, low price.  You say you want less fat, capitalism will produce food in which the fat has been replaced by sugar.   You say you want less sugar, capitalism will replace sugar with cane syrup.  You say you want simple foods with only a few ingredients, capitalism will ensure that three of those ingredients are sugar, fat, and salt.  Natural foods? Capitalism will find a way to source commercial additives naturally.  Local foods?  Capitalism will build factory farms locally.

This tendency was on my mind as I read The Hungry Brain, by Stephan Guyenet.  I learned of the book from Scott Alexander’s recent review, and Guyenet’s blog had previously been recommended to me by several very smart people.  Scott’s review is thorough, which spares me the effort of recapping every argument in the book; however, it seems to me Scott reads the book through a certain lens (asking whether weight loss is a matter of willpower, and what the role of genes is) whereas I read it through another.  For that reason, I will focus on what I think the book’s argument has to say about two questions:

  1. What should individuals do if they want to lose weight?
  2. What policies or social trends might help reduce obesity?

Guyenet presents evidence for the following:

  1. Obesity is caused primarily by overeating in general; not by lack of exercise, and not by overeating specific foods (e.g. carbohydrates or sugar.)
  2. Overeating is caused by disruptions in two physiological systems.  Meal-to-meal, we tend to overeat foods that are highly “palatable” and/or have high “food reward”, which roughly corresponds to what we call “junk food.”
  3. However, meal-to-meal overeating in itself wouldn’t be enough to cause obesity, because the body has a long-term “adiposity set point” – a certain level of fat the body tries to “defend”, secreting more or less of a hormone called leptin to regulate appetite in the long term.
  4. The problem is that something about the modern diet also damages the leptin system, which leads to a condition called “leptin resistance” that raises the body’s adiposity set point.  This is how people become – and stay – obese.
  5. It’s not entirely clear exactly what damages the leptin system; we can be fairly sure it’s something about the food we eat because the easiest way to make rats obese is to give them human junk food.  Guyenet thinks the simplest explanation is that the same foods that cause us to overeat meal-to-meal – those that have high “palatability” and/or “food reward” – also damage the leptin system and thus cause overeating and obesity in the long term.
  6. Damage to the leptin system is at least partially reversible; removing high-palatibility and/or high-reward food from the diets of rats or humans often reverses leptin resistance, lowers the adiposity set point, and leads to weight loss.  Certain other healthy behaviors (exercise, relaxation, adequate sleep) also seem to help reduce leptin resistance.

I’ve used the gangly “and/or” construction for a reason: I think it’s enormously important that we disentangle exactly which properties of foods lead to obesity.  Because an overly simplistic, depressing restatement of Guyenet’s dietary advice is “Eat foods that taste worse” – or as Scott says:

Lest I end on too positive a note, let me reiterate the part where happiness is inherently bad and a sort of neo-Puritan asceticism is the only way to avoid an early grave.

Just to drive the point home: Guyenet also notes that people tend to overeat when presented with a wide variety of foods, so to be safe, you should stick to a diet that’s both bland and repetitive (link is April Fool’s joke, but kind of not.) This advice, if taken at face value, is discouraging to accept both as an individual and for a society:

  • As an individual, I should never eat anything that tastes good.
  • As for society, I’m pessimistic about getting capitalism to provide food that tastes worse.  And I’m not especially optimistic about getting any alternative economic system to provide food that tastes worse, either – presumably we would only want to adopt an alternative if it generally makes things better.

On the upside, his advice suggests a simple life hack for weight loss:

  1. Take an ordinary salt shaker and drill the holes out slightly larger.
  2. Fill it with dirt and carry it with you at all times.
  3. Whenever you eat something, sprinkle dirt on it first to make it less palatable.

The other good news is that it’s not entirely clear what the exact relationship is between “palatability”, “food reward”, “tastiness”, and “damages your leptin system.”  Guyenet himself, in his response to Scott, hints at a loophole:

BTW, low-carb folks often have a knee-jerk reaction to the low-reward thing that goes something like this: “I eat food that’s delicious, such as steaks, bacon, butter, etc. It’s not low in reward.” But it is low reward in the sense that you’re cutting out a broad swath of foods, and an entire macronutrient, that the brain very much wants you to eat.

I’m not sure I fully grasp what he’s saying there, but maybe there’s some air between “food reward” and “tastes good” – different varieties of tastiness, so to speak.  For example, perhaps the type of tastiness found in foods that are high in sugar, fat, and salt is the “bad” kind of tastiness that causes leptin resistance, whereas the type of tastiness found in, say roasted beets is the “good” kind of tastiness that doesn’t cause leptin resistance (this may have something to do with the distinction between “craving” and “liking.”) If that were the case, I could focus on eating “good tasty” foods and avoiding “bad tasty” foods.  And assuming that capitalism will always be optimizing the heck out of something, “good tastiness” seems like the way to go.  I’m disappointed that Guyenet doesn’t explain these distinctions more clearly, although it’s probably the case that science doesn’t fully know yet.  I have noticed that Guyenet seems to have kind words for the Paleo Diet, relative to other popular diets – he doesn’t believe its specific scientific claims, but he seems to think the mix of foods it allows is a relatively healthy one.  So maybe he thinks most Paleo foods are good-tasty, rather than bad-tasty.

Or maybe there’s no such thing as “good tastiness,” and the Dirt Shaker Diet is the future of weight loss.  I’ll get to work on the Instructable.

(Note: The original version said “…the simplest, most depressing restatement…”, which I changed in response to the author’s comment.)

Addendum: A conversation with a friend reminded me that I wanted to say something about moderation and thresholds as a possible counter to “this seems puritanical.”  Imagine we rate all foods by their tastiness, on a scale of 1 to 10.  And imagine we have evidence that foods with a tastiness of 9.3 or higher damage the leptin system, but that foods below that threshold don’t do much damage.  In that case, a sensible hedonist would probably aim to eat foods that are very tasty, but below the dangerous threshold.  And likewise, it is plausible that consumer demand could direct capitalism toward producing those foods.

3 comments on “Book Review: The Hungry Brain

  1. Hello,

    Thanks for your review. I wanted to briefly clarify a couple of things. You suggested that my book offers this advice:

    “-As an individual, I should never eat anything that tastes good.
    -As for society, I’m pessimistic about getting capitalism to provide food that tastes worse. And I’m not especially optimistic about getting any alternative economic system to provide food that tastes worse, either – presumably we would only want to adopt an alternative if it generally makes things better.”

    I realize you’re probably exaggerating the message to illustrate the point. But a more accurate version is: “all else being equal, food that is more rewarding will favor a higher calorie intake”. Put that way, it sounds more reasonable and fits better with common sense. I’ve never suggested, including in the book, that a person should “never eat anything that tastes good” in order to avoid fat gain. In fact, I explained that some of the foods eaten by hunter-gatherers are tasty– like honey and the mongongo nut– while the overall diet is pretty bland.

    I realize the food reward evidence invites analogies about puritanism, but these sorts of analogies turn a scientific argument into a moral one and shut off critical thinking. The evidence in the book speaks for itself and requires no religious or moral justification– food reward is simply a biological lever that you can pull if it suits your goals.

    A couple of relevant details from the book. The first one is that the key aspect of reward that drives us to eat is the motivation, not the pleasure per se. Pleasure is just a convenient marker that tends to travel with motivation.

    Second, there are many ways to influence eating behavior and changing food reward is only one of them. Using the principles I outlined, you could construct a diet and lifestyle that is slimming without reducing the pleasure value of the diet. However, it won’t be as slimming as it could be because you’re leaving an important lever untouched.

    Constructing a slimming diet/lifestyle inevitably involves sacrifice. The question is, which sacrifices are most acceptable to you?

    • Hi Stephan, thanks for your comment. I changed the wording of the sentence before those bullet points in a way that, I hope, shows that I don’t actually believe that’s the best restatement of your advice. It sound like the “motivation versus pleasure” thing is your description of the distinction that is most interesting to me. If I’m trying to minimize the pain of dietary tradeoffs, I might look for foods that are in some way “pleasurable” but not as “motivating.” Does that sound right? My gut sense is that a high-reward food like macaroni and cheese is both pleasurable and motivating, whereas a food like asparagus might be in some sense just as “pleasurable” as macaroni and cheese, but not as “motivating”?

  2. […] of The Hungry Brain are “neo-Puritan”, and I more or less repeated that claim in my review of the book.  However, it could be argued that every diet plan is puritanical – after all, […]

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