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A Modern Pharmacist · July 26 · 28 min

Using GLP-1s Without Losing Muscle or Bone

GLP-1 pens are transforming weight loss — but almost nobody using them is protecting their muscle or bone while it happens. In this episode, I go through how to use them properly, from both a prescriber's side and a patient's side. Everyone remembers the number from the STEP 1 trial: 40% of weight loss on semaglutide was lean mass. But newer data on tirzepatide shows that figure closer to 25% — genuinely comparable to a normal diet and exercise plan. I explain why DEXA scans, the standard way we measure this, can actually be misleading: lean mass isn't just muscle, and some of what gets flagged as "loss" might really be beneficial fat clearing from inside the muscle itself. I'm honest about the evidence gap too — no completed trials have yet controlled for protein intake and resistance training specifically in people on GLP-1s. Two studies, LEAN-PREP and STAY-LEAN, are running right now, but nothing's published yet. Everything I recommend is extrapolated from the wider weight-loss literature, not proven in this specific population — and I think that's an important distinction to be upfront about. I break down the two things that actually help: hitting 1.6-2g of protein per kilogram daily with a proper leucine threshold each meal, and resistance training — which can be as little as twice a week if you're just starting out. Then I go into the bone health risk nobody talks about: osteopenia, osteoporosis, the SELECT trial's fracture data, why postmenopausal women are especially vulnerable, and why the old 400-800 unit vitamin D guidance is now outdated. Informational only, not medical advice — always speak to your own healthcare provider. New episodes of A Modern Pharmacist drop weekly.

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GLP-1 pens are transforming weight loss — but almost nobody using them is protecting their muscle or bone while it happens. In this episode, I go through how to use them properly, from both a prescriber's side and a patient's side.

Everyone remembers the number from the STEP 1 trial: 40% of weight loss on semaglutide was lean mass. But newer data on tirzepatide shows that figure closer to 25% — genuinely comparable to a normal diet and exercise plan. I explain why DEXA scans, the standard way we measure this, can actually be misleading: lean mass isn't just muscle, and some of what gets flagged as "loss" might really be beneficial fat clearing from inside the muscle itself.

I'm honest about the evidence gap too — no completed trials have yet controlled for protein intake and resistance training specifically in people on GLP-1s. Two studies, LEAN-PREP and STAY-LEAN, are running right now, but nothing's published yet. Everything I recommend is extrapolated from the wider weight-loss literature, not proven in this specific population — and I think that's an important distinction to be upfront about.

I break down the two things that actually help: hitting 1.6-2g of protein per kilogram daily with a proper leucine threshold each meal, and resistance training — which can be as little as twice a week if you're just starting out.

Then I go into the bone health risk nobody talks about: osteopenia, osteoporosis, the SELECT trial's fracture data, why postmenopausal women are especially vulnerable, and why the old 400-800 unit vitamin D guidance is now outdated.

Informational only, not medical advice — always speak to your own healthcare provider. New episodes of A Modern Pharmacist drop weekly.

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