Weight fluctuations

Your weight fluctuates by one to two kilos over the course of a day, sometimes more – and almost none of it is fat. One kilo of body fat equals around 7,000 kcal; nobody can overeat or cut back that much in a single day. What moves the scales is mostly water: in your gut, your muscles and your tissues. Once you know that, you won't let the number in the morning ruin your day.

The most common causes: salty food makes your body hold on to water to keep its salt concentration stable – after pizza or ready meals, the scales often show an extra kilo. Carbohydrates fill your glycogen stores, and every gram of glycogen binds about three grams of water: a pasta night after a few low-carb days can quickly add two kilos, which disappear just as fast. After intense training, slightly irritated muscles retain water for repair. The menstrual cycle often brings one to two kilos of water retention in its second half. On top of that come gut contents, how much you drink, heat, stress and lack of sleep.

How to weigh yourself sensibly: always under the same conditions – in the morning after going to the toilet, before breakfast, without clothes. Either once a week on the same day, or daily while keeping an eye on the weekly average; many apps show the trend as a smoothed line. If the average changes over two to three weeks, it's real. Everything else is noise.

Important for your peace of mind: scales that show two extra kilos after a lovely weekend haven't “undone everything” – the water will be gone within a few days. Conversely, a sudden drop after a stomach bug isn't fat loss. If the daily number stresses you out, weigh yourself less often or not at all: a tape measure, your waistband and your fitness tell you just as much.

By the way, children shouldn't weigh themselves regularly – their weight is a matter for routine check-ups with the doctor, not for the bathroom.