"I don't feel full yet"

This one is said in good faith. You're halfway down the plate and you check in with your stomach, and it reports nothing much. You don't feel full. So you carry on, which seems the sensible thing to do. Then, a quarter of an hour after the meal, fullness arrives all at once, and there's far more of it than you wanted.

The belief assumes that your sense of fullness is a live reading, like a fuel gauge. It isn't. It runs behind.

Your body judges how much you've eaten in several ways. A review of the subject in a leading medical journal describes the main ones. There's the stretching of the stomach wall as it fills. And there's a set of hormones released by the gut as food reaches it, which tell the brain that food has arrived. The first responds as the stomach fills. The second depends on food moving on through the stomach and into the intestine, and that takes a while. You'll often hear that it takes twenty minutes for the brain to register fullness. I couldn't trace that figure to any one study, so I wouldn't lean on the number. The general point is sound, though. The signals that say "that's plenty" are still arriving after the meal has ended.

Anyone who's used an old shower knows the problem. You turn the tap, nothing changes for ten seconds, so you turn it further, and then you're scalded. The delay makes you overshoot. With a meal, the faster you eat, the more you can get down in the gap before the signals arrive.

That has been tested. A pooled analysis of 22 experiments looked at what happens when people are made to eat the same meal quickly or slowly. The slow eaters ate less. The important detail is that they weren't hungrier for it. There was no difference in hunger at the end of the meal, or up to three and a half hours later. The fast eaters had taken in more food and got nothing extra for it in satisfaction. The authors note that the studies varied a lot in method and in the size of the effect.

This gives us a better way of reading your own signals. Enough is an early, faint signal. It shows up as a drop in eagerness more than as any feeling in the stomach. The next mouthful matters a little less than the last one did, and you look up from the plate and start talking. Fullness comes later and louder. If you wait for fullness before you stop, you'll overshoot at every meal, because by the time you feel it you're already well past enough. You were full ten minutes ago, and the news has only just arrived.

A reasonable worry follows from this. "If I stop before I feel full, I'll be hungry again in an hour." You might, the first few times, because you may stop too early while you're learning where enough is. If you're properly hungry an hour later, eat something. That's what food is for, and this book never asks you to go hungry. But the pooled experiments suggest it happens less than you'd fear. People who ate less by eating slowly weren't hungrier hours later.

The practical point is about pace and one pause. You don't have to chew each mouthful thirty times or put your fork down between bites, unless you want to. Halfway through the plate, stop for a minute. Have a drink of water, say something to whoever's at the table, and let the signals catch up a little. Then ask the question from chapter 2. You may find the answer has changed since you sat down.