GLP-1 muscle-loss risk estimator

How this is estimated (and the research behind it)

The baseline share. Reviews of the trial data put lean mass at roughly 15 to 40 percent of the weight lost on a GLP-1 medication.¹ Within that spread, the medication matters. The estimator uses a baseline of about 33 percent for semaglutide and other GLP-1s, and about 26 percent for tirzepatide, the value measured in the DXA substudy of the SURMOUNT-1 trial.^1,4

Why two scenarios. The share of loss that is muscle is not fixed. Without enough protein and without resistance training, the estimate sits toward the high end of the published range. With both in place, it moves toward the low end. The size of that shift comes from a meta-analysis where resistance training offset about 93.5 percent of the lean mass that caloric restriction alone would cost.²

Your current-habits estimate. The headline number scales between those two scenarios using your reported protein habit and resistance training. Protein and training both count, with training weighted as the primary driver because the offset in the research is a training effect. Protein enables it: benefit to fat-free mass leveled off near 1.6 g/kg of body weight, which is the target used here for the high-protein setting.³

Lean mass at risk. If you enter a goal weight, the tool multiplies each scenario's lean-mass share by the total weight you plan to lose, giving an approximate range of lean mass at stake. This is a projection from population ranges, not a prediction of your specific outcome.

Honest limits

Every number here is an estimate assembled from group averages. The 15 to 40 percent range is wide because trials differ in population, dose, and how body composition was measured, and DXA itself carries error. The 93.5 percent offset is a single meta-analytic figure that will not hold identically for every person or program. Your genetics, training quality, sleep, and starting body composition all move the real result. Treat this as a framework for a conversation with your clinician, not a measurement, a prediction, or medical advice.