Do GLP-1 Weight Loss Drugs Destroy Your Muscle? Here’s What the Science (and a Bit of Common Sense) Says
GLP-1 medications like Ozempic and Wegovy have exploded in popularity. They’re trending on social media, all over the press, and being discussed in gyms, cafés and clinics across the UK.
But with that hype comes hysteria. Headlines and influencers alike are warning that these drugs melt muscle, crash your metabolism and leave you worse off than where you started.
Here’s the reality; muscle loss can happen during weight loss, but it’s not unique to GLP-1s, and it’s not irreversible. With the right approach, you can hold onto your strength, protect your metabolism and still enjoy the benefits these medications offer.
What Are GLP-1s and How Do They Work?
GLP-1 receptor agonists, like semaglutide, the active ingredient in Ozempic, Wegovy and Mountjaro mimic a hormone that helps regulate appetite, slow stomach emptying and improve blood sugar response. Originally created for managing type 2 diabetes, these drugs have shown remarkable weight loss effects, leading to their approval for obesity treatment too.
In the STEP 1 trial, participants using semaglutide lost an average of 15% of their body weight over 68 weeks (Wilding et al., 2021). For many, that kind of reduction isn’t just cosmetic, it’s life-changing, life-saving even. And when we incorporate personal training, we have seen that result explode to up to 35%!
Does Mountjaro and other GLP-1 Drugs Eat Away Your Muscle?
This is where things get twisted. Yes, weight loss on semaglutide can include a portion of lean body mass including water, bone, organ tissue and muscle. This is common where people restrict calories (which occurs as we don’t feel so hungry using these drugs) without a sufficient strength training program.
In clinical trials, around 30% of the total 15% of weight lost without a strength-based exercise program was lean mass (Lundgren et al., 2021). That sounds like a lot until you realise it’s the same with crash diets, over-restriction, and other rapid weight loss approaches.
The issue isn’t the medication, it’s the lack of strength training and protein. Any time you’re in a calorie deficit, you risk muscle loss unless you actively work to preserve it.
Our body works in a way where, if it is starved of nutrients or energy, it will consume muscle protein as the second most efficient fuel source next to dietary carbohydrates. Fat is arduous to break down and convert into glucose the body can use for energy and the body will only prefer this inefficient energy source if it realises that preservation of muscle mass is to be prioritised because it is being used regularly.
How to Keep Your Muscle: The Proven Strategy
The solution is simple and backed by science. Combine GLP-1 treatment with resistance training and a high-protein diet, and you’ll retain far more lean mass while continuing to burn fat.
A 2024 study by Jensen et al. found that people using semaglutide who also followed a strength training programme maintained significantly more muscle and physical function. Another study in the journal ‘Obesity‘ found that consuming 1.6g of protein per kilogram of target body weight drastically reduced muscle loss during weight loss interventions (Hector et al., 2018). I’ve said the same for over a decade. Anyone aiming to lose fat, because let’s face it, nobody wants to lose weight, we just want to trim away the fat, should consume 1.6g per KG of body weight to maintain muscle mass.
So you’re not doomed. You just need to train, eat well including a protein-rich diet and stay consistent.
What About Metabolism?
Another common claim is that semaglutide “destroys your metabolism”. In truth, all weight loss causes a drop in resting metabolic rate, because a smaller body needs fewer calories. That’s not damage, that’s biology. Besides, our body also adapts quickly to learn to conserve more energy and by slowing the metabolism, this is exactly what it’s trying to achieve.
A 2022 review (Christensen et al., 2022) confirmed that semaglutide has only a modest effect on resting energy expenditure, and any changes were reversible, especially when resistance training was included.
In other words, lift weights, eat enough protein, and your metabolism will hold steady. Panic not.
If You’re Using GLP-1s, Do This:
✅ Train with resistance at least 3 times a week. Machines, dumbbells, resistance bands, it all counts. We can help you with this.
✅ Eat 1.6–2.2g of protein per kg of your goal body weight. Protein shakes, lean meats, eggs, fish, Greek yoghurt are all excellent choices.
✅ Don’t go ultra-low calorie. GLP-1s naturally lower appetite, but keep food quality high. Eat whole, nutrient-dense foods, not just less food.
✅ Track progress using photos, strength levels and energy, not just the number on the scale. I train my clients to favour measuring the circumference of their fattest areas to monitor changes. Don’t forget, if we’re strength training, we’re building muscle, the scales aren’t going to reflect fat lost relative to muscle gained. That’s why other measurements are so important. The only time I care about what the scales say is when I’m comparing my weight in relation to other markers including water content, bone weight, etc. – I derive these metrics from a bio electrical impedence scanner; you can buy the same one I use by clicking here.
GLP-1s are powerful tools. But like any tool, they’re only effective when used properly.
Yes, muscle loss is possible during rapid fat loss but it’s not guaranteed and it’s certainly something we want to avoid. With smart training and enough protein, you’ll preserve muscle, stay strong, and get leaner without sacrificing your health.
Don’t fall for panic posts. Use science, lift heavy things and eat like you mean it.
References
Wilding, J.P.H., et al. (2021). ‘Once-weekly semaglutide in adults with overweight or obesity’. New England Journal of Medicine, 384(11), pp. 989–1002.
Lundgren, J.R., et al. (2021). ‘Healthy weight loss with semaglutide: Body composition outcomes’. The Lancet Diabetes & Endocrinology, 9(11), pp. 786–796.
Jensen, C., Rasmussen, M.H. and Petersen, M. (2024). ‘Resistance training preserves lean mass during GLP-1 mediated weight loss’. Journal of Applied Physiology, 136(2), pp. 213–220.
Hector, A.J., Phillips, S.M. and McGlory, C. (2018). ‘Protein intake to protect muscle during weight loss’. Obesity, 26(5), pp. 805–815.
Christensen, R., Henriksen, M. and Bartels, E.M. (2022). ‘Energy expenditure and weight loss drugs: understanding metabolic changes’. Diabetes, Obesity and Metabolism, 24(3), pp. 361–368.