Body composition: why weight is not the goal, but fat, muscle, and waist are

A Belgian mathematician invented the body mass index in the 1830s for population statistics, not for an individual — he wrote that himself. Scales cannot distinguish a kilogram of muscle from a kilogram of fat, or a litre of water from either one. In a single night, weight can jump by two kilograms: a salty dinner, extra carbohydrates (each gram of glycogen holds three grams of water), the week before menstruation, or too little sleep. A woman who weighs herself every morning and draws conclusions is living on a roller coaster that has nothing to do with fat. Read more — why scales lie; section — scales, tape measure, and photos.

A kilogram of muscle burns about 13 kcal a day at rest, while a kilogram of fat burns about 4.5. The difference seems small until you multiply it: a woman with 25 kg of muscle and a woman with 18 kg, at the same weight, differ by 90 kcal a day simply by existing — that is 4 kg of fat per year without any effort. And here is the key point: after 30, without strength training, muscle is lost at a rate of 3–8% per decade, and “the same weight at 45 as at 25” almost always means less muscle, more fat, and a different silhouette at the same number. Muscles as an engine — muscles and energy expenditure; section — fat and muscle.

Subcutaneous fat on the thighs is an aesthetic feature and an energy reserve; metabolically, it is almost harmless. Visceral fat — around the liver and intestines — is an active organ that releases inflammatory substances and hormones, interferes with insulin, and is linked to diabetes, heart disease, and even dementia. Scales cannot see it, and it is not always visible in the mirror: a “thin person with a belly” may have more of it than a heavier woman with fat on her thighs. It is measured with a tape measure at navel level: 80 cm is the risk threshold, 88 is high. And it is precisely this fat that disappears first on a low-carbohydrate diet — the waist shrinks before the scales acknowledge it. Visceral fat, thin with fat.

During the first two weeks, water is lost — up to 2–3 kg. Then the rate drops to 0.3–0.7 kg per week, and this is not a plateau but normal: a kilogram of fat equals 7000 kcal, and it cannot be burned faster. A true plateau is four weeks with no change in either weight OR waist circumference. The causes, in order of frequency: snacks have returned, portions have grown, sleep is under 7 hours, too little salt means water is being retained, workouts have stayed the same while the body has adapted to them. And there is one cause people do not know about: recomposition — fat is lost, muscle is gained, the scales stay still, and your jeans become loose. Plateau, recomposition; section — plateaus and recomposition.

Participants in a weight-loss TV show were measured six years later: their metabolism was 500 kcal per day lower than it should have been for their weight — the body remembered starvation and conserved energy. This is adaptive thermogenesis, and it is strongest after severe deficits and without strength training. The method bypasses it in three ways: the deficit is created through pauses, not hunger within the eating window; muscles are maintained with strength training; protein is high. The body receives no “starvation” signal and does not activate energy conservation. Set point — why weight returns after diets and how to prevent it.

Scales, measuring tape and photos — how to measure the truth. Fat and muscle — what each does in your body. Plateaus and recomposition — when weight stays the same but the body changes. The foundation is the method and training; about muscles after 45 — bones and muscles after 45.