The source article links to a reference for the 40 percent claim, which itself links to a couple articles that aren't available without a JAMA account.
I can't read the original sources there, but what makes you say its obviously bullshit?
"Studies suggest muscle loss with these medications (as indicated by decreases in fat-free mass [FFM]) ranges from 25% to 39% of the total weight lost over 36–72 weeks. This substantial muscle loss can be largely attributed to the magnitude of weight loss, rather than by an independent effect of GLP-1 receptor agonists, although this hypothesis must be tested. By comparison, non-pharmacological caloric restriction studies with smaller magnitudes of weight loss result in 10–30% FFM losses."
The "surprising" part is kinda bullshit, and implies there's something special about glp-1s. It is the opposite of surprising that weight loss includes a lean mass loss.
That said, being skinnyfat is probably bad for you and the idea that you should work to preserve/build muscle and not only lose weight is a good one.
From the abstract:
"Studies suggest muscle loss with these medications (as indicated by decreases in fat-free mass [FFM]) ranges from 25% to 39% of the total weight lost over 36–72 weeks. This substantial muscle loss can be largely attributed to the magnitude of weight loss, rather than by an independent effect of GLP-1 receptor agonists, although this hypothesis must be tested. By comparison, non-pharmacological caloric restriction studies with smaller magnitudes of weight loss result in 10–30% FFM losses."
The "surprising" part is kinda bullshit, and implies there's something special about glp-1s. It is the opposite of surprising that weight loss includes a lean mass loss.
That said, being skinnyfat is probably bad for you and the idea that you should work to preserve/build muscle and not only lose weight is a good one.