Before you start

This is a short book and you can read it in two or three sittings. It's about one habit, which is stepping on the bathroom scale every morning and letting the number decide what kind of day it's going to be. Not the weight. The number, and what it does to the next twelve hours.

I'm going to argue three things. The first is that the habit makes sense from the inside. The scale is quick, it's objective, it answers a question you care about, and it feels like the one honest thing in the house. The second is that the number it gives you on any single morning isn't what you think it is. The scale weighs everything that is currently in you and on you, and from one day to the next most of what changes is water, food that hasn't left yet, salt, the stored fuel your muscles keep, and for many women the point in the month. A single morning's reading tells you almost nothing about fat, and the mood it sets is a response to noise. The third is practical. There are three honest ways to stop the number running your morning, and chapters 17 to 21 set them out so you can pick one and keep it for a month.

This isn't a weight-loss book. It won't tell you whether you should lose weight, and it won't give you a diet, a target or a number to aim at. Some readers will want to lose weight and some won't, and the argument here is the same for both. If you're in a programme that asks you to weigh, chapter 22 is written for you.

Three cautions.

If the number decides whether you eat at all, or you're eating very little, or you're making yourself sick or taking laxatives after eating, or you spend a lot of the day thinking about your weight and shape, that is beyond this book. The NHS lists those among the signs of an eating disorder and says to see a GP as soon as you can. The charity Beat has a helpline and a website, and the NHS page points to both.

If you've felt low most of the day, most days, for a fortnight or more, and the scale is one of the few things that still gets a reaction from you, the NHS says to see a GP. The number can wait until you have.

And if a doctor or nurse has asked you to weigh yourself every day for a medical reason, because of heart failure, for instance, or during pregnancy, keep doing exactly what they've asked. Chapter 23 says why that's different, and none of this book overrides it.

The notes at the back give my sources and their limits. Where I'm giving my own reasoning rather than a finding, I'll say so.