Why We Get Fat: And What to Do About It

Why do people get fat? The answer at the bar, in the doctor's office, and in the family group chat is usually the same: they eat too much and move too little. Science journalist Gary Taubes wrote this book to say that this answer sounds obvious, but it describes what happens without explaining why it happens.

The difference matters. Saying that someone gains weight because they take in more energy than they burn is true in an accounting sense, like saying a store closed because it spent more than it earned. But the owner wants to know what drove the spending, and Taubes argues that obesity science skipped that question.

The author's proposal is to shift the focus from accounting to biology. Instead of asking how much a person eats, he asks what regulates the accumulation of fat in the body. If that regulator is out of whack, overeating and laziness may be consequences of the problem, not its origin.

Taubes points out that the idea that obesity comes from moral failing is old and runs through medicine. A fat person was supposedly fat for lack of character. That adds up to a painful bill, because someone who has tried to lose weight dozens of times and failed ends up believing they are weak.

He draws an analogy with children and teenagers. A growing boy eats a lot, but nobody says he grows because he eats too much. It feels more natural to think he eats a lot because his body is building tissue and needs raw material. The author suggests something similar may happen with people who accumulate fat.

Another example he cites is pregnant women, who gain weight and feel hungrier, yet nobody accuses them of laziness. For the author, these cases show that the body can send fat into storage first and only then demand more food to make up for the trapped energy.

The most controversial chapter deals with the rule that gaining weight is a matter of calorie balance. Taubes does not deny the physics of energy conservation, but he argues that it does not explain the cause. In his view, the rule borders on tautology: a positive balance is just another name for gaining weight. Knowing the balance turned positive does not reveal whether the body stored energy because the person ate too much, or whether the person ate too much because the body was storing energy.

He criticizes the idea that exercise solves the problem. In his view, physical activity increases hunger, and someone who goes to the gym and then devours a heaping plate may end up in the same place. Treating the body like a furnace with independent inputs and outputs would be a mistake.

This part deserves careful reading, because the author combines a strong logical argument with a contested empirical claim. The reader needs to separate his critique of simplistic explanations, which is well founded, from the hypothesis he proposes in their place.