Modest weight loss (~7%) induced by 20% calorie restriction in overweight women and men decreases lean mass and reduces absolute VO2max. Exercise protects against these effects. While the CR-induced changes might be considered physiologically appropriate for a reduced body weight, exercise preserves and/or improves these parameters during weight loss, which likely improves physical function. These findings support the notion of using exercise as an important component of weight loss programs.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5161655/#:~:text=Skeletal%20muscle%20mass%20decreases%20during,increase%20fracture%20risk%20(8).

There is nothing about the molecules of the drug that causes sarcopenia. It's the weight loss that causes sarcopenia. This has been known since before glp-1s. Once again, as I've said many times in multiple threads, they should be lifting heavy weights. I like what Dr Peter Attia says: To be a (redacted) in your 80s you need to be a (redacted) in your 40s and 50s, or else you won't be there. That's because sarcopenia also happens due to age. Patients should be targeting at least 100 grams of protein per day, and lifting heavy weights.

As for the constant diarrhea, 10-15% on glp-1's have diarrhea, less on the newer one. My suspicion in your family is the poor diets contribute to it. Most prescribers of glp-1s for weight loss preach importance of drink tons of water, and add electrolyte drinks, which gets rid of the problems you've mentioned.. Every time they urinate, it should be clear.