That’s a very good question. Unfortunately the answer is nearly undefined/very high variance depending on the person undergoing the weight loss. There’s a huge range of expected outcomes depending on history and weight loss plan.
Ideal case might be Neutral LBM: Fairly obese youngish person. No training history (say someone that was super active, but not athletic, in HS). Goes to college, walks a ton stays pretty skinny. Gets first desk job around 25-26 and gains a ton of weight. Holds onto the weight, without much activity for 2-3 years. Diets in the most careful sense (.5% of bodyweight per week for 3-5 weeks then a maintenance week, macros on point, heavy resistance training, limited intense cardio). This person might stay LBM neutral, actually gain muscle and come out with massively improved body composition both on a naive DEXA scan and in reality.
Middling case might be Low LBM loss: Person has a decent training/life history, so they are carrying some “extra” muscle vs baseline. Been overweight for a while. Weight loss is limited to .5% bodyweight per week, with 2-3 cheat days per month (but no maintenance weeks). Resistance training is decent, limited cardio. They’re going to lose some, LBM, might lose some muscle, but not too much. Exact numbers are hard, but would be reasonable to expect naive body composition to go way up (DEXA scan) and if you spent time carefully figuring out if they lost muscle/bone/other, it’d be mostly other (if not entirely other).
Pretty bad case might be High LBM loss: Average life/training history, person does intense cardio and aims for >1% bodyweight per week of weight loss. This person is going to get hit with a truck of LBM loss (absent pharmacological interventions or lucky genetics).
So the money question is where does Semaglutide stack up? We know from the paper that they didn’t provide quality training advice, but we also know that the weight loss was spread (non-linearly) over 68 weeks (simple division meaning .22% per week, when .5% per week is seen as a very muscle/LBM preserving rec’d rate). I’m away from desktop so I don’t have the study pulled up, but iirc the distribution of weight loss rates over time was very conservative/favorable to preserving muscle/LBM. We also know there was poor (if standard for diet research) compliance with the plans, b/c the weight loss average rate was much lower than expected for the diet advice that was provided.
This is why the results are concerning. If you told me someone was going to lose .5%-.7% per bodyweight per week for a month or two, then really slowly lose weight for the remainder of 68 weeks, and have professionally provided diet/training advice I would expect them to lose lower than average LBM. On the other hand, maybe it’s an effect of being given a weight loss drug and seeing your weight drop? You think “heck this is awesome, I’m just going to chill and get skinny”.
I don’t know. But, the results combined with the reports of it making people “skinny fat” coming from multiple sources, notably largely consisting of doctors that have been giving it to people and then going sounding the alarm, adds another arrow to the bundle of “maybe we pump the breaks on this, or at least go into very very carefully with professional resistance training and a well craft diet” vs (what people seem to be doing (anecdotally) of pinning semaglutide once a week and chilling.
I’m sorry I don’t know how to link comment and I addressed this question above. It’s a really good question, with very undefined answer.