The bathtub: how weight changes
Eat a little more than you burn, day after day, and the body stores the extra. A little less, and it draws on what is stored. About the same, and weight holds.
The full lesson
Picture a bathtub. The faucet is food and drinks. The drain is everything your body burns. If the faucet runs faster than the drain, the water level rises — that is a surplus, and the body stores it, mostly as fat. If the drain runs faster, the level falls — a deficit — and the body uses stored fat. When they match, the level holds: maintenance.
This is true for everyone, and it is why the same rule serves different goals: someone losing fat tilts toward a small deficit; someone building muscle tilts toward a small surplus with strength training; someone maintaining aims for balance.
But the drain is not a fixed number. Your size, muscle, age, sleep, stress, hormones, medications and illness all change how fast it runs — and how hungry you feel. So we do not do math. We tilt the tub a little and watch the level over weeks, not hours.
Remember
- Surplus stores, deficit spends, balance holds.
- Your goal decides which way to tilt — gently.
- Watch trends over weeks.