Ozempic and muscles: up to 40% of weight loss is loss of muscle mass, and what the science says

Ozempic, Wegovy, Mounjaro. GLP-1 drugs have changed the world of weight loss in recent years, and rightfully so. But a new article in Nature Reviews Endocrinology shows one side that marketing doesn't always emphasize: Up to 40% of the weight loss with these drugs is not fat, but lean muscle mass.

What is GLP-1 and why is it becoming popular?

GLP-1 (Glucagon-Like Peptide-1) is a natural hormone that the body secretes after a meal. It slows down the emptying of the stomach, signals the liver to stop producing sugar, and sends a signal to the mind: "enough to eat". Drugs like semaglutide (generic name for Ozempic and Wegovy) and tirzepatide (Mounjaro) mimic the action of this hormone for days, causing a drastic decrease in appetite.

The result: weight loss of 15-22% over a year. A result that until years ago seemed possible only with bariatric surgery.

The other side: what's going on with the muscle mass?

A team led by Henning T. Langer and his colleagues published a comprehensive review in Nature Reviews Endocrinology that unifies all the studies on the subject. The findings are uniform and alarming:

• On average, 25-40% of weight loss with GLP-1 drugs is muscle mass and not fat
• For people over the age of 60, the percentage is even higher
• Menopausal and postmenopausal women are particularly sensitive
• Patients who were already in a state of sarcopenia (muscle loss due to age) see a significant worsening

Why is this happening?

The review points to three parallel factors:

1. Severe calorie deficit: When you eat less, the body does not get enough protein for muscle maintenance. A decrease in muscle mass is a natural outcome
2. Less physical activity: Patients report fatigue, low energy and less appetite for activity. Without mechanical stimulation, the muscle contracts
3. Damage to the anabolic signal: low levels of insulin and nutritional stimulation lead to a decrease in building processes (anabolism) of proteins in the muscle

Why does it matter to your health?

Loss of muscle mass is not only an aesthetic matter. This is a big risk factor:

• Day-to-day functioning: a strong muscle is necessary to get up from the chair, climb stairs, carry objects
• Metabolism: Muscle burns calories even at rest. Less muscle = slower metabolism = weight returns after stopping the drug
• Blood sugar regulation: Muscle is the best defense against type 2 diabetes. Loss of muscle cancels out some of the benefit of weight loss for diabetics
• Sarcopenia and falls: in the +60 age group, a 5% loss of muscle mass increases the risk of falls and fractures by 30%

Practical recommendations

The researchers do not call for stopping the treatment. GLP-1 drugs are a real breakthrough. They recommend an integrated strategy:

1. Protein, protein, protein: minimum 1.2 grams of protein per kilogram of body weight per day. For exercisers: 1.6-2.0 g
2. Resistance training 2-3 times a week: weights, resistance bands, or body weight exercises. It is the most vital stimulus
3. Creatine supplement: 5 grams per day, helps preserve muscle mass (especially in adults)
4. Body composition tests: It is not enough to look at the scales. Ask the doctor for a DEXA or InBody test before and during the treatment
5. Gradual progress: if weight loss is too fast, slow down the dose

What do the pharmaceutical companies do?

The Eli Lilly company is developing a new drug called bimagrumab, an antibody that blocks the myostatin receptor (a protein that inhibits muscle growth). The combination of GLP-1 with bimagrumab shows in early studies a parallel weight loss but 90% preservation of muscle mass. If the trials are successful, this could be the next generation of slimming drugs.

The bottom line

GLP-1 drugs are a powerful tool. But the weight loss is not necessarily good if 40% of the weight you lost is muscle. Working with a nutritionist, fitness trainer, and doctor is not a luxury. is a necessary condition for long-term success.