Ozempic, Wegovy and Mounjaro: How to Keep Your Muscle

In their main weight-loss trials, semaglutide (Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound) led to large average weight loss. But the scale does not tell you what kind of weight you are losing, and in those trials a meaningful share of it was not fat.

If you are taking one of these medicines, or thinking about it, here is what the research shows and what you can do to make sure the weight you lose is mostly fat.

This article is about training and nutrition alongside your medicine. Decisions about the medicine itself, including whether it is right for you and how much you take, belong with your doctor.

Semaglutide and tirzepatide are prescription-only medicines in the US and the UK (as of October 2026): they may only be supplied against a prescription from a licensed prescriber and dispensed by a licensed pharmacy. In the US there is no FDA-approved generic version, and the FDA has warned that compounded and online "versions" are not FDA-approved, that it has had reports of dosing errors with them, and that some use different salt forms. Counterfeit pens have also been found. This is a summary, not legal advice, and may be out of date.

The short answer

• GLP-1 medicines cause large weight loss, but some of it is lean mass, which includes muscle.
• Lifting weights two to four times a week is the strongest signal you can give your body to keep muscle.
• Put protein first at every meal. These medicines reduce appetite, and protein is the easiest thing to under-eat.
• Track more than the scale. Strength, waist size and photos show whether you are losing fat or muscle.
• Tell your doctor about your training.

What the trials show

In the STEP 1 trial (Wilding and colleagues, New England Journal of Medicine, 2021), adults taking semaglutide lost an average of about 15% of their body weight over 68 weeks, against about 2% on placebo. In SURMOUNT-1 (Jastreboff and colleagues, New England Journal of Medicine, 2022), the highest dose of tirzepatide led to an average loss of about 21% over 72 weeks.

Smaller groups in both trials had body scans (DEXA) to see what that weight was made of. In STEP 1, roughly 39% of the weight lost was lean mass. In SURMOUNT-1 it was roughly a quarter.

Two things are worth knowing before you worry:

• Lean mass is not just muscle. It also includes water, organs and other tissue, so the real muscle loss is smaller than the lean-mass number.
• Any large weight loss takes some lean mass, with or without medication. People in these trials were given general diet and activity advice, not a structured strength program or a high protein target.

That second point is the opportunity. The share of muscle you lose is not fixed. Training and protein change it.

Why keeping muscle matters

• It decides your shape. Losing fat while keeping muscle is what makes you look toned rather than just smaller.
• It keeps you strong. Strength makes daily life easier and matters more every year as you get older.
• It helps your blood sugar. Muscle is where much of the sugar in your blood is stored and used.
• It protects your future. Low muscle and strength in later life are linked with falls, frailty and losing independence.

How to keep your muscle

1. Lift weights

Resistance training is the most important thing you can do. Aim for two to four sessions a week, working your whole body with exercises like squats or leg presses, presses, rows and hinges. If you are new to lifting, start light and learn good technique. It is never too late to start.

The key is progression: adding a rep or a little weight over time, which tells your body its muscle is still needed. Progressive overload explained shows how.

2. Put protein first

When your appetite is low, the meal you skip or leave half-eaten is often where your protein was. Plan around it:

• Aim for roughly 1.6 g of protein per kg of body weight a day. If you have a lot of weight to lose, base it on your goal weight instead. The free protein calculator works it out.
• Eat the protein part of each meal first, before you fill up.
• Spread it across three or four meals or snacks.
• Lean on easy, protein-dense foods when you are not hungry: Greek yoghurt, skyr, cottage cheese, eggs, milk, protein shakes, fish and lean meat.

More detail in how much protein you need.

3. Watch the rate of loss

These medicines can make weight come off fast. If the scale is dropping quickly and your strength is falling too, that is a sign you may be losing more muscle than you want. Tell your doctor rather than changing anything yourself.

4. Look after the basics

• Fibre and fluids. Constipation is a common side effect. Fruit, vegetables, beans, oats and plenty of water help. See gut health for lifters.
• Steps. Daily walking supports fat loss and health without hurting your recovery. See how many steps a day for fat loss.
• Sleep. Short sleep during a diet shifts weight loss away from fat and toward muscle. See sleep and muscle growth.

Track the right things

The scale will go down. The question is what it is taking with it. Track:

• Your weekly average weight, not single days. See how to read the scale.
• Your strength on a few main exercises. Holding or gaining strength while losing weight is the best everyday sign you are keeping muscle.
• Your waist, measured the same way each week.
• Progress photos every few weeks. See how to take progress photos.

What about coming off the medicine?

In the extension of the STEP 1 trial (Wilding and colleagues, Diabetes, Obesity and Metabolism, 2022), people who stopped semaglutide had regained about two thirds of the weight they had lost one year later.

That is not a reason to stay on or come off a medicine; that decision belongs with your doctor. It is a reason to build habits now that last without it: regular training, enough protein, daily steps and a way of eating you can keep. The muscle you keep while on the medicine is part of what helps you hold on to the result afterwards.

The bottom line

Decisions about the medicine belong with your doctor. What you control is the other half of the result: lifting with progression, eating enough protein, walking, sleeping well and tracking the right things, so that the weight you lose is mostly fat. How to lose fat without losing muscle covers those basics in more detail.