Participants agree that weight loss from any method leads to some muscle reduction unless protein intake and lifting are prioritized. A rat study is cited suggesting Tirzepatide and Retatrutide specifically lower muscle marbling, but others dismiss it as weak preclinical evidence. Human MRI data from tirzepatide trials indicate muscle volume drops roughly in line with total weight lost while intramuscular fat decreases more, potentially improving quality. Early DXA-based alarms about severe muscle loss are viewed as overstated.
What this discussion establishesWhether the cited rat study meaningfully supports claims about GLP-1 effects on marbling in people
Still openLong-term functional impacts of reduced muscle marbling in humans
Nothing here is advice.
Initial suggestions that GLP-1s lead to big muscle loss are overstated since DEXA scans mix intramuscular fat into muscle readings. Drugs such as Tirzepatide and Retatrutide specifically cut down on muscle marbling, which is intramuscular fat or myosteatosis.
Big calorie cuts without lifting and enough protein cause muscle loss whether or not GLP-1s are involved. Still, thanks to Reta I guess I would no longer count as prime.
Reta also clears marbling from the liver pretty well.
If nobody mentions my marbling at the autopsy we are going to have a problem.
I do not want to sound negative but this post misses the mark. Nobody ever claimed GLPs cause more muscle loss than losing the same weight the same way without them. The study linked is basically a rat trial and those rarely translate, so it does not add much.
The way people talk about this is confusing. Any weight loss causes some muscle drop unless protein and lifting are the priority. I keep hearing from friends and family that I will end up skinny fat, same as the line about it being cheating to use a GLP. Having high A1C and BMI is not exactly the honest route either.
That is not negative, that is just thinking critically, which science needs. The old joke about curing everything in mice still fits. The paper is only a proof-of-concept rat study meant to get funding for human work, and it does not really tell us anything new.
That is interesting and it lines up. I never pictured human muscle having marbling even though I have seen it in meat plenty of times.
A rat study by itself proves little for humans, but the muscle-loss worry did not come from nowhere. DXA scans showed lean-mass drops and people ran with that. Newer MRI work with tirzepatide shows muscle volume falls about as expected from the weight lost, yet intramuscular fat drops even more, which could mean better muscle quality overall. The early alarm about GLP-1s destroying muscle looks overstated.
Before dropping 108 pounds I probably would have looked like prime rib if you cut me open. Now it would be more like skirt steak.
I was sitting in the AC, eating well and having beers, so I might qualify too. Raising Wagyu takes years of careful high-energy feeding and keeping the animals relaxed.
If we ever crash on a desert island I will be sure to tell the locals I have low marbling.
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