Metabolic adaptation

Metabolic adaptation is the body's tendency to lower its resting metabolic rate below what would be expected, in response to a sustained calorie deficit. It's one of the documented mechanisms behind weight plateaus.

Metabolic adaptation is the body lowering its energy expenditure, in response to a sustained calorie deficit, beyond what lost body mass alone would explain. Trexler, Smith-Ryan and Norton’s 2014 review shows this happens through hormonal and neuroendocrine pathways — someone who has lost 10 kilograms can end up burning even less energy than a body that was “always” that weight would.

A fixed calorie target makes this adaptation invisible, because the target is never questioned again. In Cookrange, TDEE is only recalculated with current data when you regenerate your plan — that doesn’t cancel out the adaptation itself, it just lets you correctly diagnose a weight plateau.