Exercise and nutrition
Planned physical activity whose nutritional demands vary with intensity and duration, and which influences body composition, metabolism and the gut microbiome.
Exercise changes nutritional needs in proportion to how much you do: marginally for recreational activity, markedly for intense and regular training. The main adjustment concerns carbohydrate and protein more than calories.
Carbohydrate fuels intense efforts through muscle glycogen, whose stores limit how long a sustained effort can last. Protein supports muscle repair and building, with a higher requirement than for a sedentary person. Hydration, finally, directly determines performance: losing 2% of body weight in water is enough to impair it.
Exercise also changes the gut microbiome. This is a lesser-known effect: regular, moderate activity is associated with greater bacterial diversity and a higher proportion of butyrate-producing bacteria. The effect is independent of diet, which makes it a lever in its own right.
Two final caveats. Exercise increases the production of free radicals, but the body responds by strengthening its own antioxidant defences, hence the caution about high-dose antioxidant supplements, which can blunt this adaptation. And the energy spent in a session is generally overestimated: exercise acts mainly on body composition, cardiovascular health and muscle maintenance, rather than as a direct way of creating a calorie deficit.