The 1-to-2 pound rule
One pound of fat is roughly 3,500 calories. To lose 1 lb/week, you need a daily deficit of about 500 calories through food, movement, or both.
Above 2 lb/week, most of the extra loss comes from water and lean muscle — not fat. Rapid loss also triggers stronger hunger hormones and slows resting metabolism.
When faster loss is appropriate
Medically supervised programs (very low-calorie diets, GLP-1 medication, post-surgical) can safely produce faster loss under monitoring.
The first 1–2 weeks of any diet often shows 3–5 lb from water and glycogen depletion — that's normal and doesn't continue.
Above a BMI of 35, initial loss tends to be faster and is still considered safe up to about 3 lb/week early on.
