On a GLP-1 Medication? Here's What the Research Says About Protecting Your Muscle

Performance Lab • Fitness & Longevity • 7 min read

By Jason T., Founder, Black Ridge Performance

GLP-1 medications like semaglutide and tirzepatide have changed what's possible with weight loss, producing results that used to require bariatric surgery to achieve. But there's a side of the conversation that gets less attention than it should: a meaningful share of the weight coming off isn't fat. It's muscle. If you're taking one of these medications, or considering it, understanding this tradeoff, and what the research says you can actually do about it, matters.

Why This Matters for Men on GLP-1s

The use of GLP-1 and GLP-1/GIP medications has increased sharply in recent years, and a growing share of the men using them are over 40, an age where muscle mass is already declining naturally and is harder to rebuild once lost. Combining rapid, medication-driven weight loss with age-related muscle decline is a real consideration worth understanding upfront, not something to find out about after the fact.

What the Research Actually Shows

Multiple studies converge on a similar range: lean body mass, which includes muscle, typically accounts for roughly a quarter to as much as 40 percent of total weight lost on GLP-1 therapies, depending on the study and the specific medication. A 2025 meta-analysis of 22 randomized controlled trials found lean mass loss made up about 25 percent of total weight loss. Other research has reported figures as high as 40 percent for some medications and dosing regimens. There's an important nuance here, though. Some researchers, including exercise physiologists at UC Davis, point out that a significant portion of that reported lean mass loss may be coming from organs like the liver rather than skeletal muscle specifically, and that the muscle loss which does occur may not be meaningfully different from what happens with any significant calorie-restricted weight loss, medication or not. Newer 2025 research also suggests actual muscle loss may be somewhat less severe than earlier estimates suggested, particularly when people actively work to prevent it.

Why Muscle Loss Matters Beyond the Scale

Losing weight is the goal, but losing the wrong kind of weight comes with real tradeoffs. Skeletal muscle is your body's largest site for using blood sugar, plays a major role in metabolic health, and is a key driver of resting metabolic rate, meaning less muscle can mean a slower metabolism even after the weight comes off. Muscle also supports bone health and everyday physical function, and losing too much of it can make regaining weight easier if you stop the medication down the road. None of this is a reason to avoid these medications if they're right for you and prescribed by your doctor. It's a reason to be proactive about protecting muscle while you're on one.

What Actually Helps: Protein and Training

The research on this is genuinely encouraging. A study presented at the Endocrine Society's 2025 annual meeting found that higher protein intake was associated with better muscle preservation in patients taking semaglutide, with women and older adults appearing to be at higher risk for muscle loss and potentially benefiting the most from the extra protein. Separately, research presented at the European Congress on Obesity in 2025 found that adults taking GLP-1 medications were able to retain muscle while still losing weight by combining strength training with adequate protein intake. The practical detail that matters most is how that protein is distributed across the day. Muscle protein synthesis responds best to meals containing roughly 25 to 40 grams of high-quality protein, and spreading that across three or four meals produces a better result than concentrating most of it at dinner, which is a common pattern for people whose appetite has been reduced by these medications.

A Simple Framework to Start With

If you're on a GLP-1 medication, three things consistently show up in the research as protective: getting enough total protein, distributing it across multiple meals rather than backloading it, and doing resistance training at least a couple of times a week rather than relying on cardio alone. None of this requires a complicated plan. It means treating protein and strength training as part of the medication protocol itself, not an afterthought, and talking to your prescribing doctor or a dietitian about your specific targets, since appetite suppression from these medications can make hitting protein goals genuinely difficult without a deliberate plan.

The Bottom Line

GLP-1 medications are a genuinely powerful tool, and the muscle loss that comes with them isn't a reason to avoid them if they're right for you. It's a reason to be intentional. Enough protein, spread across the day, combined with regular resistance training, is what the research consistently points to as the way to lose fat without losing the muscle that keeps you strong, capable, and metabolically healthy long after the weight is gone.

This article is for general education and is not medical advice. GLP-1 medications are prescription drugs that carry individual risks and benefits. Always talk with your prescribing doctor before making any changes related to your medication, diet, or exercise routine.