Muscle mass

Muscle makes up around 40% of body weight in men and around 30% in women – and it's the largest organ involved in sugar metabolism. Muscles move you, keep your bones and joints stable, store carbohydrates as glycogen and take up most of the sugar in your blood after a meal. People with more muscle handle carbohydrates better and have a lower risk of type 2 diabetes, falls and back pain.

Without training, the body loses three to eight per cent of its muscle mass per decade from around the age of 30, and faster after 60 – experts call this sarcopenia. Part of the “slower metabolism” in old age is simply lost muscle. The good news: muscle can be rebuilt at any age, even at 70 or 80.

Muscle mass is at risk when you lose weight. With a large calorie deficit and no strength training, a quarter of the weight lost can be muscle – bad for strength, posture and energy expenditure, and a breeding ground for the yo-yo effect. Three things protect it: enough protein (the German Nutrition Society (DGE) gives 0.8 grams per kilogram of body weight as a guideline for healthy adults, and about 1.0 gram from the age of 65; for weight-loss phases, experts usually recommend 1.2 to 1.6 grams, spread over several meals), strength training on at least two days a week, as recommended by the WHO, and a moderate rather than drastic deficit.

Strength training doesn't have to mean a gym: squats, wall push-ups, climbing stairs and carrying the shopping all count. Children build muscle by climbing, romping and playing; for teenagers, properly supervised strength training is safe and worthwhile – the old myth that it stunts growth has been disproved.

By the way: muscle doesn't weigh “more than fat” – a kilo is a kilo. But muscle is denser and takes up less space. That's why the scales can stay put while your trousers feel looser.