Retatrutide vs mk-677 for fat loss, which is actually doing the work?

Thanks for laying this out so clearly, phd_priya. A few clarifying questions if that's okay. On retatrutide, when you mention the 24% figure from the phase 2 trial, is that directly comparable to what a research context would look like given the dosing protocols used in the trial were escalating over time? I ask because I've seen people cite that number without noting the escalation schedule, and it seems like the number without context might be misleading. Also on MK-677 and the insulin sensitivity concern, is that effect seen primarily at higher doses and longer durations, or is it documented even at what the community considers "low end" research ranges? Trying to understand whether that's a threshold effect or more linear. Genuinely trying to build a proper mental model before forming an opinion here. thanks again

interesting thread. i'll offer a different frame, i dont work primarily with either of these but ive watched a lot of friends cycle both. the thing about reta is that the appetite suppression effect is SO pronounced that its genuinely hard to know how much of the fat loss is the glucagon lipolysis mechanism versus just... eating substantially less. those are different things with different implications. not saying the mechanistic story is wrong, just that clean attribution is hard in practice. could be both, obviously. mk-677 i've observed has a weird placebo-adjacent dynamic where people feel like things are happening (vivid dreams, better sleep, "something" in recovery) and that subjective signal makes the protocol feel effective even before you look at body composition. not saying its all placebo, the data on GH secretion is solid, just that the felt sense can run ahead of the measurable outcome. both of these probably deserve a "depends what you're tracking" answer more than a clean winner

mk-677 guy here so take this with that bias noted upfront. for pure fat loss as the goal? reta mechanistically wins, i dont think thats even a debate. the glucagon arm doing real lipolysis work is a different league from mk's indirect body comp effects. but here's what the community data on mk actually shows in practice: the fat loss is slow and kind of secondary to what its doing to sleep architecture. my deep sleep on whoop went from 58min average to 91min over 8 weeks at 12.5mg. that recovery improvement is doing something, whether its fat oxidation during sleep, GH pulse quality, or just better recovery allowing better output, hard to isolate. water retention is real btw. my whoop body battery was weird for weeks 2-4. leveled out. the appetite stimulation at 25mg was too much for a fat loss protocol, dropped to 12.5 and it was manageable. if the singular goal is fat loss and timelines are short, reta. if its a longer-term body comp project with sleep/recovery as secondary metrics, mk has a case

from a compounds-as-compounds perspective: these two arent really in the same category and comparing them for fat loss is a bit like asking whether your car's engine or its tire pressure matters more for speed. both matter, different systems. reta is a receptor agonist doing active pharmacological work on three axes. mk-677 is a secretagogue, it's prompting endogenous release, not replacing or directly activating downstream targets. the ceiling on mk is whatever your pituitary can actually produce, which varies significantly by subject age and baseline GH axis function. reta has no such ceiling in the same sense. for a clean fat loss outcome in research context, if the material is properly characterized (HPLC + MS, not just HPLC, reta is complex enough that MS confirmation matters), reta mechanism wins on paper. mk data is older and softer by comparison but the safety profile is better understood. verify your reta source carefully. seen some garbage out there with retention time clustering that doesnt match the MW

not my primary research area but i ran mk-677 for about 14 weeks during a recovery block and have one short reta research window logged. mk for fat loss specifically, i didnt see much. decent sleep improvement weeks 3 onward, joint comfort was noticeable (probably the IGF-1 effect), water weight was annoying for the first month. body comp at week 14 was marginally better but honestly could have been training consistency. hard to credit mk specifically. reta was a different experience, appetite effect was real and hit fast, within the first week. the fat loss signal was clearer and faster to show up than anything ive seen in the mk/ipamorelin/CJC space. sides were GI and dose-escalation dependent like the trial data suggests. if youre asking which one actually moved the needle on fat in my logs, reta. not close. mk has a role but id frame it as recovery and sleep quality tool with fat comp as a slow secondary benefit, not the headline