The Wiki Man: If you want to diet, I’m afraid you really do need one weird rule

‘Never play cards with a man called Doc. Never eat at a place called Mom’s. And never sleep with a woman whose -troubles are worse than your own.’ These were Nelson Algren’s Three Rules of Life.

You may have noticed a few more ‘rules of life’ appearing recently. After years of our being advised to drink some forgettable number of units of alcohol every week, a new rule seems to have emerged: ‘Don’t worry much about how much you drink but do abstain from alcohol completely for at least two days in seven.’ The hottest diet of the moment, sometimes called the 5:2 Diet, lets you eat freely except for two days of fasting each week. Other diets focus on total abstinence from carbohydrates, especially sugar.

Something about this black-and-white, binary approach makes sense. For any diet or health regimen to work, it must be based on rules we find psychologically easy to follow.