"I'm hungry, not thirsty"

The two o'clock biscuit and the four o'clock one. You reach for them because you're peckish, and being peckish is being hungry, and hungry people eat. There's a popular claim that hunger is often thirst in disguise. I'm not going to make it, because I haven't found good evidence for it in that form and I think it's the kind of tidy sentence that sounds like science and isn't.

What the evidence does say is more useful. In McKiernan, Houchins and Mattes's week of hourly ratings, hunger came in two waves, around the usual meal times, while thirst ran steadily all day. So at two o'clock and four o'clock, between the waves, hunger should be low for most people, and what's there is more likely to be the steady quiet signal plus the flat hour. The biscuit doesn't answer either of those. It answers the reach, which is what the hand does when the body is uncomfortable and something is in reach.

I'd add an interpretation. The feeling at the flat hour is a general one. Heavy, dull, a bit low, wanting something. It doesn't come with a label, and the mind supplies the label that has the nearest remedy. In an office with a biscuit tin, the label is "peckish". In an office with a coffee machine, it's "tired". In neither office is the label "dry", because there's no water in sight and nobody's ever taught you that dryness feels like that.

There's a small piece of evidence that drinking water before eating changes how much gets eaten, at least in older adults. Elizabeth Dennis, Kevin Davy and colleagues had 48 overweight adults aged 55 to 75 follow a reduced-calorie diet for twelve weeks, half of them drinking half a litre of water before each main meal. The water group lost about two kilograms more. A systematic review by Rebecca Muckelbauer and colleagues found the same pattern in people dieting and no consistent effect in people who weren't. This isn't a book about weight and I don't want to lean on it. I mention it only because it suggests water does something at mealtimes beyond being wet.

The practical implication is chapter 17's glass first. At the flat hour, before the biscuit or the coffee, a glass of water and ten minutes. If you're still hungry after that, eat, and an earlier book, Eat when you're hungry, is about telling hunger from the rest. Most afternoons, the biscuit turns out to have been optional.