"Starvation mode"

The claim, as heard: "If you eat too little, your body goes into starvation mode and holds on to fat — you have to eat more to lose weight."

What the data show. There is a real phenomenon underneath: after weight loss, expenditure falls somewhat below what the new weight predicts. The systematic review of it finds this adaptation real, variable between people, and in the better-controlled studies usually modest — a few percent of expenditure. It reduces the deficit; it does not abolish it. There is no state in which a body in a sustained energy deficit stops losing tissue, because there is nowhere else for the energy to come from; the historical starvation studies show people losing weight continuously, with expenditure falling because they were losing, not instead of it. What people call "starvation mode" in practice is almost always something else: a deficit that has shrunk as the weight fell, unlogged intake, or water masking the trend for a week — the plateau page works through those.

Verdict: false as a claim; the adaptation behind it is real and grade B. Nobody needs to "eat more to lose weight", although many people need to eat more to keep losing — because a deficit that is intolerable is abandoned, not because the body refuses it.

The grain of truth. Very large deficits are a bad plan: more lean tissue lost, more hunger, more adaptation, and an eating pattern nobody sustains. The app's floors exist for this reason. That is an argument for a moderate deficit, not for the switch.

One sentence to remember: the body slows a little as you lose; it never stops — and a deficit you cannot hold fails because you stop, not because it does.