Thursday, five to eleven

It's five to eleven on a Thursday morning and you've just sent off the quarterly figures, which you'd been dreading since Monday. You're working from home. You go to the kitchen, put the kettle on and take the lid off the tin. It's an old tin with a Highland cow on the lid, and it lives on the worktop next to the kettle. You take two chocolate digestives, because you've earned them. They're gone before the tea has cooled enough to drink.

At quarter past three you hit the wall. The screen has gone grey and meaningless and your eyelids are heavy. There's a chocolate bar in the desk drawer, bought for this purpose. You eat it in four bites while reading an email. For ten minutes or so you do feel brighter. By four you're yawning again and thinking about another coffee.

At ten to nine your sister Claire rings about your mum. The carers have changed their hours again, and Claire thinks you should be doing more, and says so. The call lasts twenty-five minutes and you come off it feeling wrung out and slightly in the wrong. You fetch the tin and bring it to the sofa. You have one biscuit, then another. By the end of the programme you've had four, and you couldn't describe the taste of the last two.

On the way to bed you put the tin back by the kettle and feel a bit disgusted with yourself. You resolve to do better tomorrow. Tomorrow is Friday, and on Fridays someone always brings pastries in to the office.

You'd describe yourself as having a sweet tooth. You might say you're addicted to sugar, and you'd only half mean it as a joke. You'd say you've got no willpower. What you probably wouldn't say, because nobody looks at it this way, is that you employed sugar three times today to do three different jobs, and that it's worth asking how well it did them.

I'll use a few terms throughout. The tin is wherever your sugar lives, whether that's a tin, a drawer, a cupboard or the shop on the corner. The three jobs are reward, pick-me-up and comfort. The lift is the brief pleasure and brightening you get from eating something sweet. The dip is the tiredness that follows, usually within the hour. The credit is what sugar gets when you feel better afterwards, whether or not it had anything to do with it. Pudding is a sweet thing eaten as part of a meal because you like it, and it's the use of sugar this book has no argument with.

The habit has some regular features. This list is my own observation and not a research finding.

It happens between meals. The sweet things you eat as part of a meal are rarely the ones that trouble you.

It comes with a reason. You almost never eat a biscuit for no reason at all. There's a small story each time, about deserving it or needing it.

It's fast. The eating takes a minute or two and is usually done alongside something else, such as reading, watching or working.

The amount drifts upward. One becomes two, and two in front of the television become four, without any decision being made.

And it ends with a verdict on your character. The last feeling of the day is often mild self-disgust and a resolution, which makes no difference to what happens on Friday.

Try one thing before reading on. For the next three days, change nothing, but each time you eat something sweet between meals, note the time and which of the three jobs it was doing. Then, an hour later, note how you feel. Most people find that the same few times and the same few reasons come up every day, and that the hour-later note is less cheerful than they expected.