The Weight You Lose on a GLP-1 Isn't All Fat

Opener

GLP-1 drugs such as semaglutide and tirzepatide have changed how fast people can lose weight. In the big trials, people on them lost about 15% to 24% of their body weight, far more than diet changes or older weight-loss drugs usually produce. The scale only tells you how much weight came off, though, not what came off. A 2024 review in Diabetes Care by João Carlos Locatelli, Juliene Gonçalves Costa and colleagues at the University of Western Australia, with Bu Yeap and Daniel Green as corresponding authors, pulled together the trials that measured body composition. Their conclusion is that a large share of the weight lost on these drugs is lean mass.

Our members aren't in the situation those trials describe. They're on a set diet plan with macro ratios that are set on purpose, protein included, and a plan built that way is what's meant to guard against lean-mass loss. This lecture goes through what the review found, who it found it in, and why the plan is where the answer sits.

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1. What these drugs are

Incretins are hormones the gut releases when food arrives. They raise insulin, lower glucagon, slow how fast the stomach empties and reduce appetite. The newer obesity drugs copy them: