This page has been folded into Body Fat.
Body Fat now covers the rate-of-loss question — how fast is too fast? — in its section “How you lose the fat changes what you lose — and the body fights the deficit” and the muscle-composition treatment that follows it. The short answer is unchanged: rate is a minor knob. Two things protect a person while fat comes off: preserving lean mass (adequate protein plus resistance training) and choosing a method they can sustain; much of what people fear about speed tracks the method (protein-poor, unsupervised regimens), not the number on the scale. Supervised rapid loss — as in DiRECT’s 825-853 kcal/day total diet replacement — is safe and delivered the largest diabetes-remission signal in the corpus. The rate-vs-regain and speed-vs-muscle magnitudes remain named gaps.
See Body Fat for the full treatment, including where the fat is stored, whether losing it reaches hard outcomes, and how the answer varies by stratum.