Built on peer-reviewed research, not guesswork.
BMR formula: Mifflin-St Jeor (1990)
Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." American Journal of Clinical Nutrition, 51(2):241-247. The gold-standard BMR formula validated against indirect calorimetry, more accurate than the older Harris-Benedict equation for modern populations.
Lean-mass formula: Katch-McArdle
Katch FI, McArdle WD. Exercise Physiology: Energy, Nutrition, and Human Performance. The most accurate BMR formula for trained or leaner individuals because it calculates from lean body mass directly. Activated when body fat % is provided.
Protein recommendations: Helms / Aragon / Schoenfeld
Helms ER, Aragon AA, Fitschen PJ. "Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation." Journal of the International Society of Sports Nutrition, 2014;11:20. Schoenfeld BJ, Aragon AA. "How much protein can the body use in a single meal for muscle-building?" JISSN 2018;15:10. The 0.8 to 1.0g per pound recommendation (1.0 to 1.3g during deficits) is drawn from this body of work.
GLP-1 muscle preservation: Wilding / Christensen
Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity." New England Journal of Medicine, 2021;384:989. Emerging research indicates 25 to 40% of weight lost on GLP-1 medications without elevated protein intake and resistance training is lean tissue. The GLP-1 Optimized Protocol applies the consensus protective approach: protein bumped to 1.1 to 1.3g/lb, smaller frequent meals, resistance training emphasized.
Sleep, recovery, and metabolism
Spiegel K, Leproult R, Van Cauter E. "Impact of sleep debt on metabolic and endocrine function." The Lancet, 1999;354:1435-1439 (University of Chicago). Patel SR, Hu FB. "Short sleep duration and weight gain: a systematic review." Obesity, 2008;16(3):643-653 (Harvard School of Public Health). Walker MP. Why We Sleep (UC Berkeley sleep research). The Recovery Capacity Score is derived from this body of evidence: under 6 hours of sleep, poor sleep quality, or erratic schedules all measurably impair recovery, increase hunger hormones (ghrelin), and reduce satiety hormones (leptin), which is why your protocol adjusts the deficit when recovery is low.
Activity multipliers: TDEE estimation
Activity multipliers (1.3 to 1.9) are drawn from the consensus range used in sports nutrition literature, originally codified by the FAO/WHO/UNU expert consultations and refined by Hall et al. (NIH) and ISSN position stands. Multipliers are estimates. Actual TDEE varies based on NEAT (non-exercise activity thermogenesis). Recalibrate every 2 to 3 weeks based on what your body actually does.
A note on accuracy
All BMR formulas have a ±10 to 15% standard error, even at their best, because human metabolism is individual. Your numbers are a defensible starting point, not a final answer. Track scale, tape measurements, gym performance, energy, and sleep. If two or more of those stop improving for 14 days, recalibrate. Your body is the data; this calculator is the map.
