Why has my weight loss stalled even though I haven't changed anything?

A plateau is expected, not a sign that something has broken. Two things drive it, and they act at the same time.

The first is plain arithmetic. As you get lighter your body needs fewer calories, because it takes less energy to carry and maintain a smaller body. The deficit that once existed shrinks on its own while your intake stays put, until intake meets your new, lower need. Hall and colleagues showed with their metabolic model that an unchanged diet does not produce endless loss but steers toward a new stable weight, and that the body approaches it slowly: getting halfway takes about a year. A scale that stalls after a few months is exactly what the model predicts, even with perfect adherence.

The second is adherence that drifts. Thomas and colleagues built a model of the weight plateau itself and found that the classic stall around six months is best explained by small, recurring lapses from the diet rather than by metabolism collapsing. Intake creeps up unnoticed through slightly bigger portions, uncounted bites and looser weekends, while you genuinely feel nothing has changed.

On top of this sits a smaller metabolic adaptation: energy expenditure falls a little more than weight alone explains. Fothergill and colleagues followed Biggest Loser contestants and found resting metabolism still suppressed six years later. That was an extreme, rapid loss, so the figure is not typical, but it shows the adaptation is real. The upshot: a plateau is normal, not a fault.

"I haven't changed anything" feels true, and that is the point. We don't notice that portions have grown or that weekends have loosened, and we rarely feel that our calorie needs have fallen with our weight. None of these drifts sends a clear signal. The rapid early drop, mostly water, also sets the expectation that the scale should fall in a straight line, so a natural leveling reads as failure. Then there are the incentives. A frustrated person who believes their metabolism is broken is a perfect buyer, and the diet industry meets that with metabolism boosters, detoxes and new programs promising to break the plateau. Framing an expected plateau as a fault manufactures the very worry that sells the next fix.

Recalculate your calorie needs for your current weight, not the one you started at. The deficit needs resetting once the body is lighter. Read the scale as a trend across weeks rather than day to day, since water masks small changes. And track your food closely for a few days to catch the drift. The answer usually sits in portions that grew quietly, not in a broken metabolism.