The scale rewards you for the wrong thing. It counts every kilo the same, whether it left your waist or your quads. Two studies out this month say that distinction matters more than most people on a GLP-1 ever get told, and that the two problems feed each other.
This article summarises new research and is not medical advice. It does not give dosing or treatment guidance. Talk to your prescriber or dietitian about decisions specific to you.
Start with what the drug does to muscle. Stanford Medicine researchers, writing in PNAS on June 2, confirmed something clinicians had suspected for a while: semaglutide pulls down more than fat. Their obese mice lost about a quarter of their body weight, and skeletal muscle came off alongside the fat. The part that stings is what happened next. “It wasn’t just that there was an initial loss of muscle with the GLP-1 receptor agonist,” said first author Minas Nalbandian. “It also reduced the regenerative capacity.” Damaged muscle healed more slowly. The team is testing a compound, MF-300, to switch that repair machinery back on, and in mice it restored fibre size and strength without spoiling the fat loss. Promising. Also mice, and early.
The second study is the one that should reshape your week. At ENDO 2026 in Chicago, Dr Sajana Maharjan presented tracker data from 753 adults with obesity, measured before and after they started a GLP-1. Daily steps fell from 5,047 to 4,487. Moderate-to-vigorous activity dropped from 28 minutes a day to 22. So the weight came off and people moved less. Not a little less for a few — the steepest declines landed on men and on anyone already carrying joint or muscle pain.
Put the two findings side by side and you get the trap. The medication is quietly taxing your muscle. Your routine, left to drift, points you toward fewer steps at the exact moment muscle needs you most. Nobody on a GLP-1 decides to get weaker. It happens in the background while the scale keeps handing you good news every Monday.
Maharjan didn’t soften it: “Exercise cannot be optional for people taking these medications.”
Why care, if the number’s going down anyway? Because muscle is the easiest tissue to lose and the hardest to get back. It’s a big part of how steady you are on stairs at 70, how well your body parks blood sugar after a meal, and how much you burn at rest. Trade away a chunk of it and the weight gets easier to regain later, especially if you ever come off the drug. The scale won’t warn you about any of that. It already showed you a win.
None of this is a reason to stop your medication, and none of it is medical advice. Your dose, your training, and your protein are conversations for you and your prescriber or dietitian. What the research points at is narrower and more useful: the weeks you’re losing weight fastest are the weeks your movement is most likely to slide, and that slide is the thing worth catching early. The people who hold onto strength on these drugs tend to be the ones who keep lifting something heavy a couple of times a week and keep eating enough protein to give the muscle a reason to stay. Dull advice. It also happens to be the advice the two newest studies both circle back to.
Here’s the practical takeaway, and it’s the reason we built Traqr the way we did. Weight is one line. It’s not the line that tells you whether the weight you’re losing is the weight you wanted to lose. Watch your steps and your training next to your dose, not just the number on the scale, and you’ll see the drift Maharjan measured while you can still do something about it.
Sources
- Endocrine Society / ENDO 2026 — “Exercise decreases among people taking GLP-1 medication” (Maharjan et al., presented June 2026; data via NIH All of Us). ScienceDaily: https://www.sciencedaily.com/releases/2026/06/260614011841.htm
- Stanford Medicine — “Drug enhances muscle repair during GLP-1 weight-loss treatment in mice” (Blau lab; Nalbandian et al., PNAS, June 2, 2026). https://med.stanford.edu/news/all-news/2026/06/muscle-glp-1.html