Will Reta Rewrite Obesity?
Retatrutide is being hailed as a “trillion-dollar” weight-loss breakthrough that also spares muscle. Is this really the holy grail of body composition?
My social media feed has been blowing up over what’s being predicted to become a “trillion-dollar drug,” — Retatrutide, a.k.a. “Reta” a.k.a. “GLP-3”
Retatrutide represents the third generation of GLP-1–based weight-loss drugs.
The first generation targeted GLP-1 alone.
The next wave, like tirzepatide, hit two receptors (GLP-1 and GIP).
Now retatrutide goes a step further, targeting three: GLP-1, GIP, and glucagon. It’s currently in Phase III clinical trials.
There are two big claims grabbing everyone’s attention.
Claim #1: One-Third Weight Loss in 6 Months?!
First, the sheer amount of body weight loss: Around one-quarter total body weight loss in under a year.
*Nuance note: I’ve been hearing a claim of “one-third weight loss in six-months,” but I think the one-quarter number better represents the available data. See the phase II trial results published in The New England Journal of Medicine reporting -24.2% weight loss at 48 weeks. Although the results in women as a subgroup were -28.5%, which rounds to 30%, which in turn rounds to one-third. Compound rounding ‘for the win,’ I suppose. Additionally, phase III trial results from the TRIUMPH4 trial have been collected but not yet formally published.
Claim #2: Muscle Sparing. Get Shredded!
Second, people are claiming that it’s “muscle sparing,” allowing them to get shredded without losing lean mass — or even gaining muscle.
It’s already circulating in bodybuilding circles via the peptide gray market. And recently it exploded across mainstream social media — perhaps most notably after Andrew Huberman said on TBPN that this could be a “trillion-dollar drug” because of the dramatic weight loss and “some degree of muscle sparing.”
*Author’s note: Andrew and I are on good terms, and everyone misspeaks from time to time — myself included. As I was writing this article (Feb 27, ~5:45 AM EST), I reached out to him for clarification — either to provide an updated or corrected comment, or to point me toward data I may be overlooking (which is entirely possible). I will update this article if and when I receive his response.
Naturally, I did what I always try to do: I went digging for the data.
Especially to evaluate that second claim.
I came up short… and not just because I’m 5’8” on a good day.
All roads led back to a recent sub-study published in The Lancet Diabetes & Endocrinology examining body composition changes in patients with diabetes.
Here’s the punchline: the study does not show protection of lean mass.
In just 32 weeks, participants on reta lost over 14 pounds of lean mass (6.5 – 6.9 kg in the 8 and 12 mg dosed groups). Fourteen pounds. That’s roughly the full weight of a four-month-old infant.
Yes, fat mass dropped substantially — about 10.5 to 10.9 kg in the 8 mg and 12 mg groups.
Retatrutide clearly drives significant weight loss.
But reta was not muscle sparing. In fact, approximately 37–40% of the total weight lost was lean mass — largely muscle.
How does this compare to earlier generation GLP-1s?
Well, quoting from another article in the same journal: “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.”
So, the “Trillion-Dollar” Question:
Is reta better for sparing muscle while slashing fat?
No. No, it is not.
*That -38% on the thumbnail has new meaning now, doesn’t it?
Author’s Transparency Note
I think it’s also worth disclosing that I’ve tried to do my due diligence in looking for data I might be missing. I’ve asked around, and I’ve certainly gotten pushback. People seems to be on the Reta bullet train! But, honsetly, none of the push-back has been compelling.
Some cite results from the SURMOUNT trial on tirzepatide, noting ~26% lean mass loss. That’s still not spectacular. I wouldn’t call it muscle sparing. And, importantly, it’s also a different drug anyway.
More commonly, people quote the Lancet Diabetes & Endocrinology paper stating that the proportion of lean mass loss relative to total weight loss was similar to other obesity treatments, and that “these findings could provide reassurance that a greater proportion of lean mass is not lost with retatrutide…”
But “other obesity treatments” is vague. And bear in mind that this wording may have been decided with input from Eli Lilly, the company that stands to profit.
In fact, if you read the paper, it explicitly states that Eli Lilly assisted in writing the manuscript.
So after poking my nose around, I really can’t find anything to support the claim that retatrutide is muscle sparing compared to other GLP-1 receptor agonists.
Now, is it possible that people in the bodybuilding community are able to preserve lean mass — given resistance training, supplements, high protein intake, and potentially anabolics? Absolutely. I don’t discount that.
But based on the published data, I do not think one can reasonably claim that retatrutide is muscle sparing. Full stop.
I’m happy to look the fool if someone can present solid data.
Warm Up Over! I’m Not Done With You Yet…
Long-story short, I’m not exactly sure where the idea that reta “spares muscle” originated. But from what I can tell, it doesn’t reflect the published data.
Now, if you came here just for some myth-busting on reta, you’re all set. Feel free to sign off and have a great day.
But if you truly care about the nuances of metabolic health — the deeper physiology, the trade-offs, the mechanisms most people overlook — then stick with me.
We’ve barely scratched the surface.
In the rest of this letter, I go much deeper:
Muscle as an Endocrine Organ
Mechanisms: How GLP-1 use is associated with disproportionate lean mass loss
Solutions: Specific tips and actionable insights on how to preserve muscle while taking GLP-1s (Ozempic, Reta, or otherwise)
The Top Concern: What physicians and patients worry about most
A Troubling Finding: One result that genuinely made me angry
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