Glossary
What is adaptive thermogenesis?
Updated 2026-08-16By Chris RichardsAll terms
Definition
Adaptive thermogenesis is the extra reduction in energy expenditure during a calorie deficit that is larger than you would expect from the lost body mass alone. It is real, usually modest, and not a broken metabolism.
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Your estimate
weeks at 0.4 kg / week · ~440 kcal / day gap (3,500 kcal/lb rule — real timelines are slower)
Estimate only — verify with a weight log over 2–3 weeks. Not medical advice.
Definition
As you lose weight, burn falls because there is less of you to keep warm and to move. Adaptive thermogenesis is the extra drop on top of that — less fidgeting, a slightly cheaper rest cost, hormones shifting hunger and expenditure. Dynamic models of energy imbalance exist because the straight-line “3,500 calories per pound” rule ignores both layers.
It is not a switch that turns your metabolism off. It is one reason the same intake that produced loss in month one produces less in month four.
What to do about it
Recalculate TDEE after about 5 kg of change. Defend NEAT with a step target. Consider a diet break at maintenance if adherence is crumbling. Cut another 100–150 calories only after three weeks of a flat average — not after a noisy weekend.
The mistake people make
Reading a stall as proof you must eat 1,200 calories. Most stalls are water, under-logging, or a target that was never a deficit. Adaptive thermogenesis is the explanation you reach after those, not instead of them. The goal calculator still uses a straight line so you can see how optimistic the calendar is — then add weeks.
FAQ
Did my metabolism break?
Almost never. Expenditure falls as mass falls, and a bit extra in a long deficit. It recovers as intake and weight recover. Extreme restriction is a clinical tool, not a web-calculator output.
Will a diet break fix it?
A break at maintenance can restore some spontaneous movement and make the next cut easier to hold. It is not a reset button for a formula.
Sources
- [1] Hall KD, Sacks G, et al. “Quantification of the effect of energy imbalance on bodyweight” (2011) — The Lancet 378:826–837 (PMID 21872751)
- [2] Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIH)
General nutrition information, not medical advice. Calorie and macro targets are estimates — talk to a doctor or a registered dietitian before changing your diet, especially if you are pregnant, managing a health condition, or have a history of disordered eating.
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