> A deficit of about 4000 calories a week is healthy for a loss of about a pound. There isn't really a hard and fast rule here, it depends on the person. If yo

> A deficit of about 4000 calories a week is healthy for a loss of about a pound. There isn't really a hard and fast rule here, it depends on the person. If you are obese enough, you can engage in an extended fast with no food whatsoever (just water, vitamins and electrolytes) and lose up to a pound per day in ketosis. But obviously that should only be done with the supervision of a doctor.