How to Prevent Muscle Loss on GLP-1

The headline numbers from GLP-1 are spectacular. Up to 15% weight loss on Wegovy, over 20% on Mounjaro. But there is a detail buried in the trial data that nobody puts on the marketing material: a large share of that loss can be lean tissue, not fat. In the STEP and SURMOUNT trials, up to around 40% of the weight lost was lean mass in participants who did nothing to protect it.

Losing 20% of your body weight is a triumph. Losing it as 60% fat and 40% muscle is not the result you want. The good news is that the split is almost entirely within your control, and the interventions are simple.

Why Muscle Loss Happens on GLP-1

Three forces combine. First, the caloric deficit: when you eat far less, your body looks for energy anywhere it can, including muscle. Second, protein inadequacy: a suppressed appetite makes it genuinely hard to eat enough protein, and protein is the literal building block of muscle. Third, reduced activity: the fatigue many people feel in the early weeks leads to moving less, and muscle that is not used is muscle the body sees no reason to keep.

The body does not preferentially burn fat in a severe deficit. It burns whatever is easiest, and breaking down muscle for fuel is metabolically cheap. You have to give it a reason to keep the muscle instead.

Protein: The Foundation

Your target on GLP-1 is 1.6 to 2.2 grams of protein per kilogram of body weight per day. Most women on GLP-1 fall dramatically short, often managing half that, simply because they are not hungry.

The trick is to treat protein as a requirement, not a response to appetite. Practical ways to hit it on a suppressed appetite:

• Protein shakes when solid food feels like too much
• Greek yoghurt and skyr as easy high-protein snacks
• Eggs in any form, cheap and complete
• Lean meat and fish prioritised on your plate before anything else

Ancient + Brave make a clean grass-fed collagen that stirs into coffee, and dedicated whey and plant proteins from MyProtein and Bulk are the simplest way to close the gap on low-appetite days.

Resistance Training: Non-Negotiable

This is the part people want to skip and absolutely cannot. Resistance training is the signal that tells your body to keep its muscle. Even two sessions a week of basic compound movements, such as squats, rows and a press, is enough to dramatically shift the fat-to-muscle ratio of your weight loss. Sub-analyses of the STEP trials consistently show that participants who trained preserved far more lean mass.

You do not need a complicated programme. Two full-body sessions a week, a handful of compound lifts, progressing the weight slowly over time. That is the whole prescription.

Supplements That Actually Help

Most supplements do nothing for muscle. Two have real evidence in this specific context:

• Creatine monohydrate. One of the most studied supplements in existence. It helps preserve muscle and strength during periods of low caloric intake, exactly the situation you are in. Three to five grams daily, no loading phase needed.
• Collagen with vitamin C pre-workout. Supports connective tissue, tendons and ligaments, which take more strain as you train in a deficit.

Protein Timing

Spreading protein across three to four meals beats loading it all into one. For women over 40, aim for 30 to 40 grams per sitting to clear the leucine threshold needed to actually trigger muscle protein synthesis. Smaller, frequent doses with one larger anchor meal works well on a suppressed appetite.

The Bottom Line

Muscle loss on GLP-1 is common but not inevitable. Hit your protein target every single day, lift weights at least twice a week, add creatine, and spread your protein across meals. Do that and the overwhelming majority of what you lose will be fat, leaving you lighter, stronger and far more likely to keep the weight off. For the deep dive on protein, read our complete protein on GLP-1 guide and our supplements guide. To compare medications by how they affect body composition, see our GLP-1 comparison.