Body-recomp simulator — Pro tool overview

Summary

Project a 12 or 24-week trajectory of modeled fat-mass loss vs lean-mass loss with a GLP-1-aware coefficient.

What this tool does

Projects a weekly trajectory of modeled fat-mass loss versus lean-mass loss across a 12- or 24-week horizon. A toggle applies a literature-pooled GLP-1 lean-mass attrition coefficient when GLP-1 therapy is indicated.

How the math works

Stylized linear model. Coefficients are sourced from STEP-1 (Wilding 2021), SURMOUNT-1 (Look 2025), Conte 2024 meta-analysis, and Neeland 2024 review for the GLP-1 lean-mass-loss fraction. Non-GLP-1 baseline uses Heymsfield 2014 lean/fat partitioning. Protein-protection threshold draws on Murphy/Koehler 2022 and ISSN 2017. Resistance-training threshold draws on Longland 2016 and Sardeli 2018. Energy balance uses Wishnofsky 1958 (kcal/kg fat) and Hall 2011 (kcal/kg LBM).

What the tool will not do

It is educational, not predictive. Many factors that shape body composition (sleep, NEAT, training history, individual metabolism) are not in this model. It does not save scenarios between visits.

Inputs the tool takes

• Current weight
• Body-fat percent
• Daily calorie deficit
• Daily protein intake
• Weekly resistance-training sessions
• GLP-1 therapy toggle

What the tool returns

• Weekly fat-mass and lean-mass trajectory
• Total loss across the chosen horizon
• Lean-loss share of total loss (the hero result tile)
• Inline citations for the constants used

Cited literature

• STEP-1 (Wilding 2021, NEJM)
• SURMOUNT-1 (Jastreboff 2022, NEJM)
• Heymsfield 2014, Am J Clin Nutr
• Hall 2011, Lancet (energy-balance modeling)
• Longland 2016 protein + resistance training
• ISSN 2017 protein-intake position stand

Coefficients reviewed 2026-04-28 · full citations in RECOMP_SIMULATOR.md.

See it in action

The body-recomp simulator is a pepSmart Pro tool. See what Pro includes.