Muscle Loss on GLP-1s: Why Protein Matters During Weight Loss

For many people taking GLP-1 medications, eating less is part of what makes weight loss possible. Medications such as semaglutide and tirzepatide can reduce appetite and help you feel fuller for longer, often making smaller portions feel more satisfying. But when you're eating considerably less than you used to, there's something else worth thinking about: are you getting enough nutrition to support your muscles?

When you lose weight, not everything you lose is necessarily body fat. Some loss of lean mass can occur as well, including muscle. And because GLP-1 medications can significantly reduce overall food intake, it may become easier to fall short on protein, particularly if you're eating smaller meals or skipping meals because you simply aren't hungry.

That matters because muscle does much more than change how your body looks. It contributes to strength, movement, physical function and your ability to stay active, making muscle preservation an important consideration during weight loss.

So, if you're currently taking a GLP-1 medication—or considering one with your healthcare professional—here's what you should know about muscle loss, protein and making the food you eat count.

First, which GLP-1 medications are we talking about?

When people talk about GLP-1 medications, they're referring to a group of prescription medicines that act on the body's GLP-1 system. They are primarily used to manage type 2 diabetes and/or obesity, depending on the particular medicine and its approved indication.

Some of the names may already be familiar. In Australia, several GLP-1 and related dual GIP/GLP-1 medicines are approved by the Therapeutic Goods Administration (TGA), including: 

• Semaglutide – sold under brand names including Ozempic, Wegovy and Rybelsus

• Tirzepatide – sold as Mounjaro and works as a dual GIP/GLP-1 receptor agonist

• Dulaglutide – sold as Trulicity

• Liraglutide – sold under brand names including Saxenda and Victoza

Other GLP-1 receptor agonists have included exenatide (Byetta and Bydureon) and lixisenatide (marketed as Lyxumia in Australia). 

It's important to note that these medicines aren't interchangeable and they're not all approved for the same purpose. For example, Ozempic is approved in Australia for adults with type 2 diabetes, whereas Wegovy contains the same active ingredient, semaglutide, but is approved for chronic weight management in eligible patients. Mounjaro is approved for both type 2 diabetes and chronic weight management.

They're also prescription-only medicines and should be used under the guidance of an appropriate healthcare professional.

Why can muscle be lost during GLP-1 weight loss?

When you're losing weight, the number on the scales doesn't tell you what type of weight you've lost. Ideally, most of the reduction would come from body fat, but during significant weight loss, the body can also lose some lean mass.

This isn't unique to GLP-1 medications. Lean mass loss can occur with weight loss in general, particularly when someone is consuming fewer calories than their body needs. Research suggests that the proportion of lean mass lost with GLP-1 and related medications is broadly comparable with that seen in other approaches that produce substantial weight loss.

GLP-1 medications can, however, make this particularly relevant because they can significantly reduce appetite and overall food intake. When you're feeling fuller sooner or simply aren't as interested in food, you may eat smaller meals or eat less frequently. While this can support weight loss, it can also make it easier to fall short on protein and overall nutrition if you're not paying attention to what those smaller meals contain. 

Lean mass doesn't mean muscle alone

There's an important distinction to make when looking at studies about GLP-1s and body composition.

You may see reports suggesting that a certain proportion of weight lost while taking medications such as semaglutide or tirzepatide comes from “lean mass". But lean mass isn't the same thing as skeletal muscle. It includes muscle as well as other non-fat tissues and body water, so a reduction in measured lean mass shouldn't automatically be interpreted as the same amount of muscle being lost.

What the research does show is that GLP-1-assisted weight loss generally results in greater reductions in fat mass than lean mass, but some loss of lean tissue can still occur.

How much an individual loses can also vary. Factors such as the amount and speed of weight loss, age, starting body composition, physical activity, protein intake and whether you're doing resistance exercise can all influence what happens to your muscle during a period of weight loss.

Why does preserving muscle matter?

When you're focused on losing weight, it's easy to pay attention mainly to the number on the scales. But how you lose that weight matters too. Preserving muscle while reducing excess body fat can help support your strength, physical function and ability to stay active during and after weight loss.

Muscle helps you stay strong and active

Muscle isn't just important for athletes or people trying to build a particular physique. You rely on your muscles throughout everyday life — whether you're walking, climbing stairs, carrying groceries, getting up from a chair or exercising.

Maintaining muscle therefore helps support your strength, mobility and physical function, allowing you to continue doing everyday activities comfortably and independently.

Muscle becomes increasingly important as you age

We naturally tend to lose some muscle mass and strength as we get older, particularly later in life. Significant weight loss can introduce another opportunity for lean tissue to be lost, making muscle preservation especially worth considering for older adults or anyone who already has relatively low muscle mass or strength.

Maintaining adequate nutrition and continuing to use your muscles through physical activity can therefore become an important part of supporting healthy ageing and long-term mobility.

Protein's role in preserving muscle 

When your appetite is smaller, the nutritional quality of what you do eat becomes particularly important. For people losing weight while taking GLP-1 medications, that means making sure protein doesn't unintentionally get pushed aside.

Protein provides the amino acids your body uses to maintain and repair muscle tissue. During weight loss, getting enough protein can help support the preservation of lean mass, particularly when it's combined with resistance exercise. 

How much protein should you aim for?

There isn't one protein target that's right for everyone.

For healthy Australian adults, general protein requirements vary according to age and sex. According to Dietitians Australia, the approximate daily protein requirement is 0.75 grams per kilogram of body weight for adult women and 0.84 grams per kilogram for adult men. For adults over 70 years of age, this increases to approximately 1 gram per kilogram of body weight per day. However, protein needs during active weight loss may be higher, particularly when preserving muscle is a priority. 

Recent expert guidance around GLP-1-assisted weight management notes that protein intakes around 1.2–1.6 grams per kilogram per day have been proposed during active weight loss. However, this shouldn't be treated as a universal target, particularly because calculating protein requirements from actual body weight can overestimate needs in some people with overweight or obesity. 

Your individual needs can depend on factors such as your:

• Age and body composition

• Activity level and exercise routine

• Rate and amount of weight loss

• Overall energy intake

• Existing health conditions, including kidney disease

If you're unsure how much protein is appropriate for you, particularly if you have an existing medical condition, a dietitian or healthcare professional can help establish a suitable individual target.

Spread your protein across the day

It's not only your total daily protein intake that's worth considering. Rather than relying on one large protein-rich meal at the end of the day, try to include a source of protein across your meals and snacks.

This approach can be particularly practical while taking a GLP-1 because large meals may be difficult to manage when your appetite is reduced.

Prioritise good-quality protein foods

Protein doesn't have to come from one particular food or from supplements. A varied diet can provide protein from both animal and plant sources.

Useful options include:

• Eggs

• Fish and seafood

• Chicken and other lean poultry

• Greek yoghurt, cottage cheese and milk

• Beans, chickpeas and lentils

• Tofu and tempeh

• Nuts, seeds and nut butters

What if you don't feel like eating much? 

If getting enough protein from regular meals becomes difficult, protein-rich snacks, bars or shakes can also be useful for some people. They shouldn't necessarily replace a varied, balanced diet, but they can provide a convenient way to supplement your protein intake when appetite, portion size or a busy schedule makes whole meals less practical.

This is where convenient options such as Chief Nutrition can come in handy. Their Beef Bars are made with 100% grass-fed Australian beef and provide a high-protein savoury snack, while the range also includes protein bars and snacks that are lower in sugar, giving you different options depending on what you feel like eating. These can be particularly handy when you're on the go or simply looking for an easy way to supplement the protein you're already getting from meals.

Protein isn't the only part of the equation: Use your muscles too

Getting enough protein is an important part of supporting muscle during weight loss, but protein works best alongside actually using your muscles. 

Why resistance exercise matters

When you perform resistance exercise, your muscles have to work against some form of resistance. This provides a stimulus that encourages the body to maintain and adapt muscle tissue. When combined with adequate protein, resistance training can help support the preservation of muscle mass and strength during periods of weight loss.

You don't necessarily need a gym

Resistance exercise doesn't have to mean heavy weights or complicated gym workouts. Depending on your fitness level and abilities, it could include:

• Bodyweight exercises, such as squats or modified push-ups

• Resistance bands

• Free weights or weight machines

• Exercises that involve pushing, pulling, lifting or carrying against resistance

The important part is that your muscles are being regularly challenged in a way that's appropriate for your current ability.

For Australian adults, the Department of Health, Disability and Ageing recommends muscle-strengthening activities on at least two days each week, alongside regular aerobic physical activity.

What about walking and cardio?

Walking, cycling, swimming and other aerobic activities are still valuable for cardiovascular health, fitness and overall wellbeing, so there's no reason to abandon them. However, if preserving muscle is one of your goals during weight loss, it's worth making room for activities that specifically challenge your muscles, rather than relying on cardio alone.

If you're new to strength training, have an existing health condition or aren't sure what type of exercise is suitable while taking a GLP-1 medication, speak with your doctor, physiotherapist or accredited exercise professional about an appropriate starting point.

Don't focus on protein so much that you forget everything else

Protein deserves plenty of attention when you're trying to preserve muscle during weight loss, but it shouldn't come at the expense of the rest of your diet. When GLP-1 medications reduce your appetite and you're eating smaller amounts overall, making those meals nutritionally balanced becomes even more important.

Make your smaller meals nutrient-dense

Rather than thinking only about how many grams of protein you can fit into each meal, aim to include a variety of nutrient-dense foods where your appetite allows.

Alongside protein-rich foods, your diet should still include:

• Vegetables and fruit for fibre, vitamins, minerals and other beneficial nutrients

• Whole grains and other high-fibre carbohydrates for fibre and energy

• Healthy fats from foods such as nuts, seeds, avocado and olive oil

• Adequate fluids to support hydration and normal body function. Nausea, vomiting, diarrhoea and reduced food and fluid intake associated with GLP-1 medicines can increase the risk of dehydration in some people. 

You don't necessarily need to fit everything into one large meal. If your appetite is smaller, smaller meals and snacks spread throughout the day may be more manageable.

Conclusion: Aim to lose weight, not your strength

GLP-1 medications can be an effective tool for weight management when prescribed appropriately, but successful weight loss isn't only about seeing a smaller number on the scales. It's also worth thinking about what you're preserving along the way.

Some loss of lean mass can occur whenever you lose a significant amount of weight. When GLP-1 medications reduce your appetite and overall food intake, however, it becomes particularly important to make sure you're still giving your body the nutrition and stimulus it needs to support muscle.

That doesn't mean you need to dramatically increase your protein intake or start an intensive gym routine. Instead, focus on practical, sustainable habits: include good-quality protein throughout the day, make smaller meals nutritionally worthwhile, incorporate appropriate resistance exercise and continue eating a varied, balanced diet.

And remember that everyone's needs are different. Your age, activity level, rate of weight loss, existing muscle mass and overall health can all influence how much protein and exercise may be appropriate for you. If you're struggling to eat enough, losing weight very quickly, noticing changes in your strength or unsure whether you're meeting your nutritional needs, speak with your doctor or an Accredited Practising Dietitian for individual guidance.

Make Every Gram of Protein Count

Chief Nutrition Healthy Snacks & Protein Supplements

When your appetite is smaller, convenient protein options can make it easier to add protein to your day without needing another large meal. Explore Chief Nutrition's range of protein powders, bars and protein-rich snacks at Aussie Pharma Direct for simple ways to supplement the protein you already get from everyday foods.

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