NEAT

NEAT — non-exercise activity thermogenesis — is the energy you burn doing everything that is not sleep, eating, or deliberate exercise. Walking to the kitchen. Standing at your desk. Carrying groceries. Fidgeting in your chair. Loading the dishwasher. For most people it is the second-largest component of TDEE after BMR, and it is the component with by far the widest inter-individual variability.

Why NEAT matters more than the label suggests

Classic work by James Levine at the Mayo Clinic established that NEAT differences between individuals can exceed 2,000 kcal/day at extremes, and 800–1,000 kcal/day is routine. Two 80-kg, 35-year-old men with identical BMR and identical exercise routines can have maintenance-calorie numbers that differ by 1,000 kcal simply because one stands more and moves more throughout the day.

This is the biggest single reason two people "eating the same" have radically different weight-change outcomes.

NEAT drops during deficit — a lot

Among the most robust findings in the adaptive-thermogenesis literature: when humans go into a meaningful caloric deficit, NEAT falls. Subjects take fewer spontaneous steps, stand less, fidget less. This is not always conscious and is not always noticeable on a wearable, because wearables primarily pick up the large-movement component.

The practical implication: the TDEE your tracking app calculated before you started cutting is almost certainly not your TDEE four weeks in. NEAT has likely declined, pulling your actual maintenance lower than the model predicts.

How wearables measure NEAT

Consumer wearables — Apple Watch, Fitbit, Garmin, Whoop, Oura — infer NEAT from accelerometer-derived step counts, posture estimates, and (in some devices) heart rate. The resulting "active calories" number is a reasonable directional signal for large movement. It tends to undercount low-level fidget movement and postural thermogenesis, which can be sizable.

How to act on NEAT

• During a cut: protect NEAT deliberately. Walk. Stand. Take the stairs. The NEAT you preserve is calories you don't have to remove from intake.
• During a bulk: expect NEAT to rise. People in surplus move more, and some of the surplus is dissipated as low-grade fidget thermogenesis rather than stored.
• When an app's TDEE disagrees with your weight trend: NEAT drift is the most likely explanation.

NEAT is the reason tracking is imprecise

No consumer tracking app asks, "how much did you fidget today?" because there's no practical way to measure it. Wearables pick up the big-movement fraction of NEAT and miss most of the low-amplitude fraction. This is the single largest reason predictive-equation TDEE estimates routinely miss by 200–400 kcal/day for a given individual. For trackers who keep hitting their calorie target but not losing the expected weight, "I must be NEAT-suppressing more than I realise" is a hypothesis worth treating seriously — usually well before blaming the food log.