GLP-1 Medication and Strength Training: How to Protect Your Muscle

GLP-1 medicines like semaglutide (Wegovy) and tirzepatide (Mounjaro) have changed what is possible for people living with obesity. But if you lift, or want to start, there is an important question: how do you lose the fat without losing the muscle you have worked for?

How GLP-1 medicines work

GLP-1 is a hormone your gut releases after you eat. It helps you feel full and helps control blood sugar. GLP-1 medicines mimic it, which reduces appetite, so most people eat noticeably less. Tirzepatide also acts on a second hormone receptor, called GIP.

The results can be dramatic. In the STEP 1 trial of 1,961 adults with overweight or obesity, people taking weekly semaglutide lost an average of 14.9% of their body weight over 68 weeks, compared with 2.4% on a placebo.

The muscle question

When you lose a lot of weight by any method, some of it is lean mass, which includes muscle. A 2024 review of GLP-1 trials found that the share of weight lost as lean mass varied widely, from about 15% to over 40%, depending on the medicine, the people studied and how it was measured.

The same review offers some reassurance. The relationship between weight loss and lean mass loss looked broadly similar to other weight-loss methods, and MRI scans suggested the changes in muscle were largely adaptive, with less fat stored in the muscle itself.

Still, muscle matters for strength, everyday function and healthy ageing, so it is worth protecting. The review highlights the two main tools: resistance training and enough protein. A 2025 joint advisory from four US nutrition and obesity organisations also called for preserving muscle and bone through resistance training and an appropriate diet during GLP-1 treatment.

Lift weights two or three times a week

The NHS recommends strength exercises on at least two days a week for all adults. On a GLP-1 medicine, that is the minimum worth aiming for. A simple full-body plan, three days a week, covers every major muscle and leaves plenty of time to recover.

• Keep the weights challenging. Stop each set with one or two good reps left in the tank. Lifting meaningful weights is the signal that tells your body to hold on to muscle.
• Progress gradually. Add a rep or a little weight when you can. Our body recomposition guide explains double progression, a simple way to do it.
• Scale back, do not stop. On days when side effects hit hard, do fewer sets rather than skipping the session.
• Keep walking. Daily walks add activity without leaving you wiped out for your next session.

Prioritise protein

With a much smaller appetite, protein is easy to under-eat, and the 2024 review notes that GLP-1 treatment may even shift food preferences away from high-quality protein. For people who lift, the International Society of Sports Nutrition recommends 1.4-2.0 g of protein per kg of body weight a day. If you have a lot of weight to lose, ask your prescriber or a dietitian what target is right for you.

• Eat the protein on your plate first, before you fill up.
• Spread it across three or four smaller meals rather than one or two big ones.
• Lean on easy options: Greek yoghurt, skyr, cottage cheese, eggs, milk and protein shakes.
• Track it for a few weeks so you know where you stand. The free BarbellBites app shows your protein against your target each day.

Training around side effects

Stomach side effects are common, especially when the dose is going up. In STEP 1, they were the most frequently reported:

• Train at the time of day you usually feel best, and keep sessions shorter on rough days.
• Avoid a big meal right before training.
• Drink regularly. The UK government's guidance notes that these side effects can sometimes lead to severe dehydration.
• Tell your prescriber about side effects that are severe or do not settle, and report them through the MHRA Yellow Card scheme.

Keeping the weight off

GLP-1 medicines work while you take them. In the STEP 1 extension, people who stopped semaglutide regained about two-thirds of the weight they had lost within a year, ending up 5.6% below their starting weight on average.

Exercise helps. In a Danish trial, 195 adults with obesity who had lost weight on a low-calorie diet were followed for a year. The placebo group regained 6.1 kg on average, while exercise and liraglutide, an older GLP-1 medicine, each helped people keep the weight off. Those who did both lost a further 3.4 kg.

That is why the habits you build during treatment matter most: regular strength training, plenty of protein and a way of eating you can keep up for good.

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