Research

Energy balance

Fat-free mass (FFM) is the primary determinant of 24-hour energy expenditure, explaining 81% of the variance between individuals, while spontaneous physical activity (fidgeting) accounts for significant residual variability (100-800 kcal/d) independent of body size.

Your daily energy needs are mostly determined by your lean muscle mass, but your daily habits of movement (fidgeting, pacing, general activity) significantly alter that number. Two people with the same weight and muscle mass can have vastly different calorie burn rates simply based on how much they move spontaneously throughout the day. Do not rely on static 'one-size-fits-all' calorie targets; adjust for your actual daily activity levels.

GoodQualifiesHIGH confidence
fat-free mass (FFM) as estimated by densitometry is the best available determinant of 24-h energy expenditures (24EE) and explains 81% of the variance observed between individuals... A large portion of the variability of 24EE among individuals, independent of differences in body size, was due to variability in the degree of spontaneous physical activity, i.e., 'fidgeting,' which accounted for 100-800 kcal/d in these subjects.
Éric Ravussin et al. · Journal of Clinical Investigation · 1986

Why this rating

High-quality observational data using a gold-standard respiratory chamber method on a large, diverse sample (n=177), with reproducibility checks.

Source

Determinants of 24-hour energy expenditure in man. Methods and results using a respiratory chamber.

Éric Ravussin et al. · Journal of Clinical Investigation · 1986

DOI 10.1172/jci112749

cross_sectional · n=177Cited 1,159×
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DOI resolved against Crossref · corpus check 2026-06-10

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