How to Maintain Muscle While Losing Weight on GLP-1 Medication

How to Maintain Muscle While Losing Weight on GLP-1 Medication

If you've lost 10 kg, how much of that was actually body fat?

If you're taking a GLP-1 medication and the number on the scales is falling, that's a win.

But there's another question worth asking:

What exactly did you lose?

When your body weight decreases, the change isn't necessarily made up entirely of body fat. Weight loss can involve reductions in fat mass, lean mass, water and glycogen.

This doesn't mean GLP-1 medications are "causing muscle wasting" or that losing some lean mass means your treatment isn't working.

It means something much simpler:

The quality of your weight loss matters.

If your goal is to lose excess body fat while maintaining as much strength, muscle and physical function as possible, what you do alongside your medication matters.

Weight loss isn't the same as fat loss

GLP-1 medications such as semaglutide and tirzepatide can be highly effective tools for helping people lose weight.

Research into these medications shows that weight loss generally includes reductions in both fat mass and lean mass.

For example, a body-composition analysis from the SURMOUNT-1 tirzepatide trial found that approximately 75% of the weight lost was fat mass and around 25% was lean mass.

That sounds straightforward, but there's an important scientific caveat:

Lean mass is not the same thing as skeletal muscle.

Body-composition techniques such as DXA measure lean tissue as a broader category. Changes in hydration, glycogen and other tissues can influence these measurements.

So we shouldn't automatically translate "lean mass lost" into "muscle lost."

The evidence is more nuanced than that.

A 2026 systematic review and meta-analysis of 20 randomised controlled trials involving more than 15,000 participants found that lean mass accounted for roughly 25–39% of weight lost with incretin-based therapies, depending on the medication and study. Importantly, this proportion was broadly comparable with other weight-loss approaches.

The message isn't that GLP-1 medications are bad.

It's that losing weight and preserving the body underneath that weight are two related—but different—goals.

Why does muscle matter?

Muscle isn't just about how you look.

It's what allows you to:

• produce strength
• climb stairs
• carry shopping
• get up from a chair
• play sport
• train effectively
• maintain physical independence
• continue doing the things you enjoy

Muscle also plays an important role in glucose disposal and metabolic health.

And as we get older, maintaining strength and physical function becomes increasingly important.

If you're losing weight in your 40s, 50s or beyond, protecting your physical capacity isn't something to worry about later.

It's something worth building now.

The GLP-1 nutrition challenge

One of the reasons GLP-1 medications can be so effective is that they can reduce appetite and food intake.

For someone who has struggled with hunger, cravings or overeating, that can be incredibly helpful.

But there is another side to the equation.

When you're eating significantly less, it can become harder to consume enough protein, energy and essential nutrients.

Some people also experience nausea, early fullness, vomiting, constipation or diarrhoea, particularly during dose escalation.

This can make eating enough even more difficult.

That's why the answer isn't simply:

"Eat less."

The better question is:

"How do I make the food I do eat count?"

The muscle-preservation strategy

At WRK, I keep the approach simple:

Lift. Eat enough protein. Support your nutrition.

These three things don't guarantee that you'll preserve every gram of muscle during weight loss.

Nothing can.

But they provide a practical framework for supporting muscle, strength, recovery and physical function while you're losing weight.

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1. Lift

Resistance training gives your body a reason to maintain strength and muscle.

When you're in an energy deficit, your body has less energy available. Providing a regular resistance-training stimulus tells your body that the muscle you're carrying is still needed.

That's why resistance training should be a fundamental part of a GLP-1 weight-loss strategy.

And you don't need to become a bodybuilder.

You don't need complicated workouts or hours in the gym.

The latest American College of Sports Medicine position stand on resistance training reinforces an important principle:

Consistency matters more than complexity.

Train the major muscle groups regularly. Challenge yourself. Progress when appropriate. And build a routine you can actually maintain.

For most people, that's far more valuable than chasing the perfect programme.

2. Eat enough protein

Protein provides the amino acids your body needs to build and repair tissue.

During weight loss, getting enough protein becomes particularly important because you're asking your body to function with less available energy.

For someone taking a GLP-1 medication, however, knowing that protein matters is only half the battle.

The bigger challenge can be getting enough of it when you're not particularly hungry.

That might mean:

• prioritising protein within meals
• choosing nutrient-dense protein sources
• using smaller, protein-focused meals
• incorporating protein-rich snacks where appropriate
• considering liquid or softer protein options if appetite or nausea makes solid food difficult

Your individual protein requirements will depend on factors such as body size, age, activity levels, training and goals.

There isn't one magic number that applies to everyone.

The important thing is to make adequate protein intentional, rather than assuming your reduced appetite will automatically lead you to eat enough.

3. Support your overall nutrition

Protein is important.

But it isn't the entire picture.

Your body also needs adequate energy, carbohydrates, fats, vitamins, minerals and fluids to support normal function, training and recovery.

This is particularly important when appetite is significantly reduced.

Eating as little as possible isn't the goal.

The goal is an appropriate, sustainable calorie deficit that helps you lose excess body fat while still giving your body enough nutrition to support the life you're trying to live.

That means choosing foods based on more than just how few calories they contain.

When you have a smaller appetite, nutrient density matters.

Think beyond the scales

The scales are useful.

But they're only one measure of progress.

If you're using a GLP-1 medication, consider tracking some of the things that the scales can't tell you.

Are you getting stronger?

Can you lift more, perform more repetitions or handle exercises that used to feel difficult?

Are you maintaining physical function?

Can you walk, climb stairs, carry things and move through your day with confidence?

Are you maintaining your training?

Are you able to keep showing up and progressively challenge your body?

Are you building habits you can keep?

Because ultimately, weight loss isn't the finish line.

The goal is to build a body and lifestyle that can support the life you want to live.

GLP-1 medication can help you lose the weight. Your habits help determine what happens next.

GLP-1 medication can be a powerful tool for weight loss.

But medication is only one part of the equation.

Resistance training provides the stimulus.

Protein provides the building blocks.

Good nutrition supports the process.

And consistent habits help you build the strength and physical capacity to maintain your results.

You don't need to be perfect.

You don't need to train like an athlete.

And you don't need to obsess over every gram of food or every kilogram on the scales.

You simply need to give your body the support it needs while you're asking it to change.

Lose the weight. Keep your strength. Build the fitness to keep it off.

That's the foundation of GLP-1 Fitness Coaching at WRK.

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Key Research & References

• Wilding JP, et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine.
• Jastreboff AM, et al. (2025). Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight.
• Currier BS, et al. (2026). American College of Sports Medicine Position Stand: Resistance Training Prescription for Muscle Function, Hypertrophy, and Physical Performance in Healthy Adults. Medicine & Science in Sports & Exercise.
• Strategies for minimizing muscle loss during use of incretin-mimetic drugs for treatment of obesity (2025). Obesity Reviews.
• Lean Mass Changes With Incretin Therapy Versus Lifestyle Intervention (2026). Systematic review and meta-analysis of randomised controlled trials.
• Lean Mass and Musculoskeletal Preservation in GLP-1-Based Obesity Treatment (2026). Review of nutrition, exercise, supplementation and monitoring strategies.