GLP-1 medications like Ozempic, Wegovy, and Zepbound produce rapid weight loss — but not all of that loss is fat. Body-composition substudies from the major GLP-1 trials show a meaningful share of the weight lost is lean muscle tissue, and appetite suppression makes it genuinely harder to eat enough protein to prevent it. This calculator translates that research into a concrete daily protein target, a per-meal plan, and a projection of how much of your loss could be muscle versus fat.

Why GLP-1 Weight Loss Puts Muscle at Risk

Dual-energy X-ray absorptiometry (DXA) substudies of the major GLP-1 trials quantify exactly how much of the weight lost on these drugs is lean tissue rather than fat. The STEP 1 semaglutide body-composition substudy found lean mass accounted for roughly 39–45% of total weight lost, while the SURMOUNT-1 tirzepatide substudy found a smaller share, around 25%. Either way, a meaningful fraction of the number on the scale is muscle, not fat — and appetite suppression is exactly the mechanism that makes eating enough protein to counter it harder. That combination is why a GLP-1-specific protein target, not a generic weight-loss one, matters.

The 1.2–2.2 g/kg Range, Explained

The ISSN Position Stand on protein and exercise and the PROT-AGE position paper on protein needs in older adults both describe a protein range well above the 0.8 g/kg RDA for anyone active or in an energy deficit. This calculator scales your target within that 1.2–2.2 g/kg band by resistance-training frequency: about 1.3 g/kg with no training, rising to about 2.1 g/kg at 5 or more sessions per week. The multiplier moves because muscle under more mechanical load has a proportionally larger need for the amino acids that drive repair and retention.

Lean Mass vs. Total Weight

Calculating protein from total body weight overestimates the need for someone with a high body-fat percentage and underestimates it for someone lean and heavily muscled. When you enter a body fat percentage, this calculator switches the basis to lean body mass — total weight minus fat mass — giving a more individualized number. Without that entry, it falls back to total weight, which is still a reasonable estimate for most users.

Why Per-Meal Distribution Matters More on a GLP-1

Muscle protein synthesis responds to protein in a threshold pattern: below roughly 25g of high-quality protein in a single meal, the anabolic signal is blunted regardless of how much protein you eat the rest of the day. GLP-1 medications often shrink appetite enough that hitting this floor at every meal is a real challenge — this is precisely why the calculator flags meals that fall short and suggests consolidating to fewer, larger meals instead of spreading protein too thin.

Resistance Training Is Not Optional

A 2010 systematic review in Nutrition Reviews (Weinheimer et al.) found that adding exercise — particularly resistance training — to an energy-restricted diet consistently helped preserve fat-free mass compared to diet alone. No completed trial has yet isolated that same effect specifically in GLP-1 users, though a dedicated randomized trial (LEAN-PREP) was registered in 2026 to test resistance training and protein supplementation during semaglutide and tirzepatide therapy. Until that data is published, this calculator treats adequate protein (≥1.6 g/kg) plus resistance training (3+ sessions/week) as the two levers most likely to shift your GLP-1-driven weight loss toward fat and away from muscle, based on the broader body-composition literature.