Eli5: If gaining weight is simply the result of calories in and out, then why does taking certain medications (birth control, anti-depressants) commonly lead to weight gain?

Question

Eli5: If gaining weight is simply the result of calories in and out, then why does taking certain medications (birth control, anti-depressants) commonly lead to weight gain?

In: Biology

Answer 1

Those medications cannot disobey the laws of physics. They might be responsible for some water retention. Thats not excess fat tissue but is still an increase in net weight. They also might be responsible for increased appetite but that doesn’t directly point to them violating thermodynamics by creating energy.

The increased appetite doesn’t reflect the number of cells you have and thus your energy needs.

If you eat more food energy than you needed per day, the excess is stored as fat. Likewise if you don’t eat more than you needed, excess energy is consumed. CICO should not be thought of as a diet but just an energy balance equation. It helps to think of it as just income/expenditure for your bank balance.