Roughly a quarter of what you lose is not fat
Across 22 randomised trials, total weight fell 3.55 kg, fat mass 2.95 kg and lean mass 0.86 kg. Not one trial in the pool measured strength, mobility or falls.
What the study found
About a quarter of the weight lost was lean mass, not fat
Fat is not the only thing that leaves. Across 22 randomised trials of semaglutide and the drugs like it, total weight fell 3.55kg, fat mass 2.95kg and lean mass 0.86kg; semaglutide 2.4mg ranked among the best for fat loss and among the worst at holding lean mass.
The caveat · Nobody measured strength or falls
The pooled trials were short and produced only 3.55kg of loss, so those kilograms do not scale up to someone losing a seventh of their body weight; the proportion is what carries over. Lean mass as a share of body weight did not change. Not one trial in the pool measured strength, mobility or falls, so whether the loss costs anything a person would notice is untested.
What we don't know
Whether losing lean mass on semaglutide costs anything a person would notice has not been measured either way. Trials rank it weak at holding lean mass; one study with no comparison group says it was preserved.