Nutrition · foundations
Weight change comes down to energy in versus energy out. Understanding where your calories go makes every other nutrition decision clearer.
Basal metabolic rate (BMR) is the energy your body uses at complete rest just to stay alive — heartbeat, breathing, temperature, cell repair. It is the largest part of most people's daily burn, typically 60–70%. BMR rises with body size and muscle mass and falls gradually with age. The Mifflin–St Jeor equation is the most accurate common estimate.
Total daily energy expenditure (TDEE) is BMR plus everything you do: the thermic effect of digesting food (about 10% of intake), the energy of deliberate exercise, and the often-underrated energy of everyday movement — walking, fidgeting, standing (known as NEAT). TDEE is what you actually burn in a day.
Eat below your TDEE and you lose weight; above it and you gain. But as body weight changes, BMR and TDEE change with it, so a fixed calorie target produces a smaller and smaller gap over time — which is why steady progress naturally slows. Recomputing your numbers as you go keeps expectations realistic.