Can you really "damage" your metabolism?

Long-term extreme dieting can temporarily lower resting metabolic rate (metabolic adaptation), but the effect is usually reversible.

What burns more calories — muscle or fat?

Muscle. A pound of muscle burns about 6 kcal per day at rest, a pound of fat only about 2.

Can supplements boost metabolism?

Marginally. Green tea extract and capsaicin increase thermogenesis by a few percent. The effect is real but small.

Metabolism: What It Is and How to Support Your Metabolic Rate

"My metabolism is broken" is one of the most common explanations for why the scale won't move. It's usually wrong. Metabolism can slow down — but it can also be upgraded.