MythBusting GLP-1s: TRUTH About Weight Loss Medications

Thank you for listening to The Peptide Podcast. If you enjoyed the show and want to support what we do, head over to our Partners Page. You'll find some amazing brands we trust—and by checking them out, you're helping us keep the podcast going. Today, we’re diving into one of the most talked-about topics in health and weight loss right now: GLP-1 medications like semaglutide and the newer dual GIP/GLP-1s like tirzepatide. You’ve probably seen the headlines, scrolled past a few TikToks, or heard a friend mention it — but with all that noise comes a lot of confusion, half-truths, and flat-out myths. Today we’re breaking it all down. What’s real? What’s hype? And what do you actually need to know if you're using these medications — or thinking about it? Let’s separate science from scare tactics and get to the truth, one myth at a time. Myth #1: GLP-1s Cause Dangerous Muscle Loss The claim: “GLP-1s cause massive muscle loss.” Truth: This is an overstatement. Some loss of lean mass is normal with any kind of weight loss — whether it’s through diet, medication, or surgery. What studies show is that with medications like semaglutide (Wegovy) and tirzepatide (Zepbound), about 20–25% of the total weight lost comes from lean mass, and the rest is fat — which is exactly what we’re targeting in obesity treatment. That 20–25% figure isn’t unique to these meds; it’s actually pretty typical in weight loss without focused resistance training or optimized protein intake. You may also hear “You’ll lose all your muscle and become frail on GLP-1s.” Truth: You won’t “lose all your muscle.” In fact, muscle loss is preventable by maintaining adequate protein intake, resistance training, and managing weight loss pace. Furthermore, many patients gain strength and mobility as excess weight comes off. And lastly, my favorite myth is “You can’t preserve muscle on GLP-1s.” Truth: That’s completely false — muscle loss isn’t inevitable on GLP-1s if you take the right approach. You can absolutely preserve muscle by making a few intentional choices: aim for enough protein each day (a good goal is around 0.8 grams per pound of body weight), include some strength or resistance training a couple times a week, and avoid losing weight too quickly. These simple steps go a long way in protecting your lean mass while still getting all the benefits of weight loss. One study on semaglutide showed that people lost an average of about 15% of their body weight, and only around 3–4% of that was lean mass. So if someone drops 30 pounds, maybe 6 to 8 of those pounds might be lean mass—not ideal, but definitely not disastrous either, and very manageable with the right lifestyle habits. The truth is, while some lean mass loss is expected with any type of weight loss, research shows that most of the weight lost on GLP-1s is actually fat, not muscle. For example, in the STEP 1 trial, about 80% of the weight lost on semaglutide came from fat, and only about 20% from lean tissue (as we mentioned earlier). The SURMOUNT-1 trial with tirzepatide showed similar results—significant fat loss with relatively preserved muscle, especially when paired with resistance training. And that’s important, because preserving muscle during weight loss helps protect metabolism, strength, and overall health. With good nutrition and movement, GLP-1s can lead to healthier body composition—not just a lower number on the scale. Okay, moving along to the next myth … Myth #2: GLP-1s Can Cause Blindness The truth: This myth stems from concerns about diabetic retinopathy worsening, which is tied to how quickly blood sugar drops, not to the drug itself. In the SUSTAIN-6 trial (Marso et al., NEJM, 2016), a small subset of patients with pre-existing advanced diabetic retinopathy saw transient worsening—but only in those with rapid improvements in A1c. No increased rates of blindness or new-onset retinopathy have been found in non-diabetic patients using GLP-1s for weight loss. The bottom line is that those without advanced diabetic eye disease, there’s no increased risk of blindness. Patients with diabetic retinopathy should be monitored closely—but this is about glycemic management, not a direct effect of the medication. Myth #3: GLP-1s Cause Kidney or Liver Damage The truth: This is false. In fact, GLP-1 agonists may protect kidney and liver function—especially in patients with diabetes or fatty liver disease. The most recent notable study showing kidney‑protective effects of a GLP‑1 receptor agonist is the FLOW trial, which evaluated semaglutide in people with type 2 diabetes and chronic kidney disease (CKD). This double‑blind, randomized, placebo‑controlled trial included 3,533 participants followed for a median of 3.4 years and found that semaglutide reduced the risk of major kidney‑related events—including kidney failure, substantial eGFR decline, and death from renal or ...