NIH Dynamic Weight-Loss Simulator
Educational estimate only — not medical or nutritional advice. The simple 3,500-kcal-per-pound rule is a static approximation; real weight change slows as metabolism adapts. Related: The 3500-Calorie Rule: Is It Still Accurate?. Consult a physician or registered dietitian before changing your diet.
How this estimate is derived (why it differs from the 3,500-calorie rule)
The familiar 3,500-kcal-per-pound rule traces to Wishnofsky (1958), who estimated that one pound of body-fat tissue holds roughly 3,500 kcal and assumed a static body: every deficit would produce a straight-line loss. This tool instead uses the NIH dynamic energy-balance model developed by Kevin Hall and colleagues at the U.S. National Institutes of Health (NIDDK), published in The Lancet (Hall et al., 2011). That peer-reviewed model tracks fat mass, lean mass, and energy expenditure together, so it captures the metabolic slowdown that the 3,500 rule ignores.
| Assumption | 3,500-kcal rule | NIH dynamic model |
|---|---|---|
| Basis | Wishnofsky 1958 (static) | Hall et al., Lancet 2011 (dynamic) |
| Trajectory | Straight line | Curved, slowing to a plateau |
| 12-month loss from a 500 kcal/day deficit | ≈ 52 lb (linear arithmetic) | ~roughly half (model-dependent) |
| Accounts for metabolic adaptation | No | Yes |
The dynamic model shows the body-weight response to a sustained intake change has a half-time of about one year and asymptotes to a steady-state plateau — not endless linear loss (Hall et al., 2011). Model simulations indicate a sustained 500 kcal/day deficit produces roughly half the weight loss the 3,500 rule predicts over 12 months, because energy expenditure declines as weight drops (Hall et al., 2011; Thomas et al., International Journal of Obesity, 2013). Real-world data support the persistence of this adaptation: Fothergill et al. (Obesity, 2016) found resting metabolic rate remained about 500 kcal/day below prediction six years after major weight loss.
Sources
- Hall KD, Sacks G, Chandramohan D, et al. “Quantification of the effect of energy imbalance on bodyweight.” The Lancet. 2011 Aug 27;378(9793):826–837. doi:10.1016/S0140-6736(11)60812-X. PMID: 21872751. (Retrieved 2026-08-11, via NIDDK / Europe PMC.)
- Wishnofsky M. “Caloric equivalents of gained or lost weight.” American Journal of Clinical Nutrition. 1958;6(5):542–546. (Origin of the 3,500-kcal rule; retrieved 2026-08-11.)
- Thomas DM, et al. “Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Dynamic adaptation of the body to weight change.” International Journal of Obesity. 2013. (Retrieved 2026-08-11.)
- Fothergill E, Guo J, Howard L, et al. “Persistent metabolic adaptation 6 years after ‘The Biggest Loser’ competition.” Obesity. 2016. (Retrieved 2026-08-11.)
Educational use only. This simulator provides estimates for educational and informational purposes. It is not medical, nutritional, or dietary advice. The dynamic model is an NIH/NIDDK research model for adults; individual results vary. Always consult a qualified healthcare provider or registered dietitian before starting or modifying a nutrition or exercise program.