Exercise for fat loss & maintenance

Exercise alone typically produces only ~1.5–3 kg of loss over months — roughly 30–40% of what the calories-burned arithmetic predicts — because the body compensates by raising appetite and cutting spontaneous movement. Meaningful loss from exercise needs a lot of it: ACSM puts the threshold around 225–420 min/week. Diet drives the deficit far more reliably. Evidence ●●●●○

Doubly-labelled-water work (Pontzer) suggests the body partly ‘constrains’ total energy expenditure — you burn less extra than a treadmill readout claims (roughly 25–30% is offset on average). Whether expenditure is strictly capped is actively debated, with 2025 data on both sides. The safe statement: exercise burns real calories, just fewer net than advertised.

The volume of activity that barely moves the scale during weight loss is almost exactly what predicts maintaining it. People in the National Weight Control Registry — who’ve kept ~30 kg off for years — average about an hour a day of activity (~2,500–2,800 kcal/week), mostly walking, confirmed by accelerometer. Evidence ●●●●○ (partly self-selected; caveat below)

Most maintenance evidence is observational — people who choose to move more keep weight off better, which is not the same as proving the exercise caused it. Leaner maintainers also find activity easier. The association is robust and biologically plausible, but state the causal magnitude with humility.

Aerobic exercise preferentially strips visceral fat — the dangerous kind — often with little scale movement, and it improves blood pressure, lipids and insulin sensitivity largely independent of weight. Cardiorespiratory fitness is one of the strongest mortality predictors we have: each 1-MET higher is ~13% lower all-cause mortality, and being fit blunts much of the risk of a higher BMI. Evidence ●●●●●

Matched for time and effort, interval training and steady-state produce similar fat loss — HIIT’s real advantage is finishing in ~40% less time. Ignore two persistent myths: the ‘fat-burning zone’ (low intensity burns a higher percent of fat but fewer total calories) and the ‘afterburn’ (EPOC adds only ~50–200 kcal). Pick the cardio you’ll actually do.