How to protect your muscle while losing weight on a GLP-1 medication

Losing weight on a GLP-1 or GIP/GLP-1 medication usually means losing some muscle along with fat. That is true of almost every way of losing weight, but the amount of weight lost on these drugs is large enough that it is worth planning for. Here is what the trials show, what is still uncertain, and what you can do about it.

What the trials show about muscle and weight loss

In the SURMOUNT-1 trial, adults took Zepbound (tirzepatide), a GIP/GLP-1 medication, for 72 weeks. A DXA scan substudy of 160 participants found that about 75 percent of the weight lost was fat and about 25 percent was lean mass, the same split seen in the placebo group (Look et al., Diabetes Obes Metab 2025). Lean mass is not only muscle. It also includes water, organs, and connective tissue.

A recent review of GLP-1 body composition studies, mostly on Wegovy (semaglutide) and Saxenda (liraglutide), reached a similar conclusion. These medications reduce fat mass, especially deep belly fat, with a modest proportional drop in lean mass (Bhandarkar et al., Curr Opin Endocrinol Diabetes Obes 2025).

So the medication is not uniquely hard on muscle. The issue is size. In the pivotal trials, average weight loss was about 15 percent of body weight with semaglutide and more with tirzepatide (Wilding et al., NEJM 2021; Jastreboff et al., NEJM 2022). A quarter of a large loss is still a real amount of lean tissue.

Why it matters more for some people

Muscle drives strength, balance, and how well your body handles blood sugar. After 40, most people already lose some muscle each decade without trying. If you are 55, lose 50 pounds, and also lose a meaningful share of your muscle, you may be lighter but weaker than you want to be.

The trial data are reassuring on average. They do not tell us how any one person fares, and most body composition substudies are small. Early evidence suggests muscle quality and function matter as much as the scan number, and those are harder to measure. We treat this as a reason to be intentional, not a reason to avoid treatment.

Resistance training is the most useful tool

Lifting weights, using resistance bands, or doing bodyweight strength work two to three days a week gives your body a reason to hold on to muscle. A network meta-analysis of 38 randomized trials in adults aged 50 and older found that resistance training, alone or with protein supplementation, improved muscle strength and physical function. Combining the two gave the best results for lean mass (Tian et al., J Nutr 2025).

Those studies were not done in people taking GLP-1 medications, so we are borrowing the evidence from a closely related situation. It is a reasonable bet, and a low-risk one.

A simple starting plan:

• Pick 6 to 8 basic movements: squat or sit-to-stand, push, pull, hinge, and carry.
• Do 2 to 3 sets of 8 to 12 repetitions, with the last few reps feeling hard.
• Add weight slowly when the last set feels manageable.
• Walk on the other days. It helps, but it does not replace strength work.

If you have joint pain, heart disease, or have not exercised in years, tell us first and we will help you set a safe starting point.

Protein and eating when your appetite is low

GLP-1 medications turn down hunger, which is the point. The side effect is that you can easily under-eat protein. A common clinical target is roughly 1.2 to 1.6 grams of protein per kilogram of body weight per day, which is about 0.55 to 0.7 grams per pound. Guidelines differ, and your kidney function, age, and other conditions matter, so treat this as a starting range to discuss with us.

Practical ways to get there when you are not hungry:

• Eat protein first at each meal, then fill in with other foods.
• Keep easy options on hand, such as Greek yogurt, eggs, cottage cheese, canned fish, tofu, and lean meat.
• Use a protein shake if solid food is hard on a nausea day.
• Drink enough water. Dehydration makes everything feel worse.

A large 2026 network meta-analysis of older adults found that whey protein paired with resistance training ranked best for muscle mass and leg strength (Lin et al., Nutrients 2026). Whey is a convenient option, but whole foods work too.

Signs to watch and how we monitor you

Muscle loss is easy to miss because the scale only goes down. We suggest tracking things that reflect function:

• Can you stand up from a chair without using your hands?
• Are stairs, groceries, or carrying a toddler getting harder?
• Is your grip weaker, or do you feel unusually tired?
• Are your clothes loose while your waist measurement barely changes, or the reverse?

Tell us if you notice these. We can review your dose, your protein intake, your labs, and your activity plan. In some cases, slowing the pace of weight loss is the right call. A body composition scan can help, but it is not required and results vary by machine.

Next steps

If you are on a GLP-1 or GIP/GLP-1 medication, or thinking about starting one, we can build a plan that protects your muscle while you lose weight. Visits are by telehealth, by appointment. Most major plans are accepted, including Medicare. Primary care should not be something you buy on top of the coverage you already pay for. Learn more about endocrinology care at Stonewood and book a visit when you are ready.