Muscle loss is one of the most common side effects when using GLP-1 medications—a personal trainer and nutritionist says these two strategies will help you keep hold of it

GLP-1 medications have revolutionized weight loss.

Designed for chronic weight management and to treat type 2 diabetes, glucagon-like peptide-1 receptor agonists such as Ozempic, Mounjaro and Wegovy essentially work by promoting weight loss through increased fullness and reduction of appetite.

These medications have been credited with helping some users with chronic obesity lose considerable amounts of weight. However, this weight loss isn’t always just fat loss.

London-based nutritional therapist and personal trainer Tomas Mitkus says it can also be coupled with significant muscle loss, unless you follow two tried-and-tested strategies to preserve it.

“One of the key drivers for body composition changes with GLP-1s is loss of muscle mass,” the founder of Healthier Sapiens tells Fit&Well.

“There is some research that shows approximately 30% of the body weight lost on GLP-1 drugs is muscle mass. If you lose 50 pounds, 15 pounds could be muscle loss.”

The body will actively catabolize muscle, Mitkus explains, as a safety mechanism.

“If you put yourself in an extreme calorie deficit, and some people on GLP-1 drugs are eating as little as 1,000 calories per day, your body will burn fat for energy,” he says.

“But because muscle is so demanding from an energy standpoint, your body will also catabolise muscle tissue. It will eat itself to prevent starvation.”

On average, one kilogram of muscle tissue requires about 10-15 calories per day to sustain itself at rest, versus about 4.5 calories for fat.

“If your body composition of muscle mass is 25kg, you will burn through roughly 250-375 calories just existing,” elaborates Mitkus, compared with around 112 calories for the same amount of fat.

That’s why being of a higher muscle mass is always encouraged by personal trainers in order to lose weight or maintain a healthy weight more easily.

So, if your body composition of muscle falls while using GLP-1s, your basal metabolic rate (the minimum number of calories your body needs to function at rest) can slow, and hormone levels become unbalanced, making it harder to keep weight off if you stop using the drugs.

That's why Mitkus urges anyone using GLP-1s—or following a weight loss diet generally—to take steps to build, or at least maintain, muscle mass rather than simply cut calories.

How to preserve muscle mass when using GLP-1 drugs

Mitkus says growing any meaningful muscle in a calorie deficit is not a realistic expectation for most. Instead, the goal should be to maintain what you have or lose as little as possible.

And his solution involves the same principles you would follow if you were dieting without GLP-1s: lift weights regularly and consume adequate protein.

1. Lift weights

Mitkus recommends strength training three to five days per week for 30-45 minutes per day—covering all of the major muscle groups.

“Aerobic exercise, like walking or running at a moderate to vigorous intensity will also be beneficial for overall good health, but the main thing is resistance training,” he says.

If you can only commit to three, make them full-body workouts, targeting all the major muscle groups, like the hamstrings, quads, glutes, chest, back and shoulders.

The specific exercise selection isn't important, so long as training is consistent, sustainable and follows the principle of progressive overload, he adds.

That means incrementally increasing the number of repetitions you perform or the amount of weight you lift week on week.

“Initially, you might feel lethargic on a lower calorie intake when using GLP-1s, but as long as micronutrient intake isn’t compromised, people tend to adapt pretty well and energy levels return,” says Mitkus.

And if you’re completely new to strength training, he always advocates working with a coach who will make workouts fun and effective, and the process more enjoyable.

2. Consume protein

To support this training schedule, Mitkus also recommends consuming adequate protein.

“Protein is extremely important for anyone lifting weights or trying to gain muscle,” he says. “You’re not going to build muscle in a calorie deficit, but if you are feeding it with enough of the right amino acids you should hopefully have enough not to lose it.”

Most GLP-1 medication comes with recommendations to consume between 1.2-1.6g of protein per kilogram of body weight.

“That’s an adjusted number, meaning it should be up to 1.6g of your ideal or target body weight,” Mitkus notes.

“But if you are working out more regularly, you could push that to 1.6-2.2g of your desired body weight, which is really what’s recommended for people strength training regularly and trying to build muscle.”

Mitkus concedes that eating more protein is easy to say but much harder to do when on appetite-suppressing GLP-1s, which can also cause side effects like nausea and vomiting.

To help hit your daily target, he suggests spreading your protein intake out across three to four protein-centric meals, and consuming more liquid or softer foods—like Greek yogurt, cottage cheese or protein shakes—which are easier to digest and less filling.