Weight-Loss Jabs and Muscle: Protein and Strength Basics

Weight-loss medications such as Wegovy and Mounjaro have gone mainstream in the UK. Researchers at UCL estimated in January 2026 that around 1.6 million adults in England, Wales and Scotland had used them in the previous year, most of them through private providers. One question now comes up again and again: what happens to muscle?

This guide explains why muscle matters while you are taking GLP-1 medication, and the two habits that make the biggest difference: strength training and enough protein. It is general information, not medical advice. Your prescriber or GP should always be your first point of contact.

Why muscle loss is a concern on GLP-1 medication

When anyone loses weight, part of what they lose is lean mass (muscle, water and other non-fat tissue), not only fat. Because GLP-1 medicines can reduce appetite sharply, people often eat far less than before, and protein intake can drop with everything else.

A December 2025 report from ukactive and Les Mills cited evidence that 20–50% of the weight lost on these drugs can be lean body mass, and called for strength-training support for everyone who uses them. Losing muscle matters because it underpins strength, balance and everyday independence, especially as we get older.

What the experts recommend

The same report points people back to the UK Chief Medical Officers' activity guidelines: muscle-strengthening activity on at least two days a week, plus 150 minutes of moderate (or 75 minutes of vigorous) activity. Nothing exotic, just consistent resistance training and good nutrition.

Habit 1: Strength train at least twice a week

Muscle responds to being used. Resistance training sends the signal your body needs to hold on to muscle tissue, even when you are eating less. If you are new to it, start simply:

• Two full-body sessions a week of 30–45 minutes are enough to begin with.
• Pick 5–6 big movements: a squat or leg press, a hinge (such as a Romanian deadlift), a push (press-up or chest press), a pull (row or lat pulldown), and a carry or plank.
• Do 2–3 sets of 8–12 reps, finishing each set with 2–3 reps still in the tank.
• Progress gradually by adding a little weight or a rep or two each week.

Appetite and energy can dip on the medication, so plan sessions for times of day when you feel best, and do not train fasted if you feel light-headed. A qualified coach can help you get started safely.

Habit 2: Prioritise protein at every meal

Protein provides the amino acids your muscles are built from. With a smaller appetite, the challenge is simple maths: you need to fit enough protein into fewer, smaller meals.

The UK reference intake for adults is 0.75 g of protein per kg of body weight per day, but many sports nutrition experts suggest that people who are losing weight and training regularly aim higher, often in the region of 1.2–1.6 g per kg. If you have kidney problems or another medical condition, ask your doctor what is right for you.

Practical ways to eat enough protein with a small appetite

• Protein first: eat the protein part of your plate before the rest, while appetite is highest.
• Spread it out: aim for 25–30 g of protein at each of three meals rather than one large serving.
• Choose dense foods: Greek yoghurt, skyr, eggs, cottage cheese, chicken, fish, tofu, lentils and edamame give a lot of protein per mouthful.
• Use liquids when solids feel heavy: many people find a smooth shake easier to manage than a big meal.

A protein shake is one convenient option when food alone falls short. A whey isolate is highly filtered, which means a high protein content per serving with relatively little fat and sugar. Mixed with water or milk, it is quick to take after a strength session or alongside a lighter meal.

Where creatine fits in

Creatine monohydrate is one of the most researched supplements in sport. Creatine increases physical performance in successive bursts of short-term, high intensity exercise, and the beneficial effect is obtained with a daily intake of 3 g. For adults over 55, daily creatine consumption can enhance the effect of resistance training on muscle strength (again with 3 g a day, alongside resistance training).

In practice, that means creatine can help you get more out of the strength sessions described above. It is not a substitute for them. Check with your prescriber before adding any supplement while you are on medication, particularly if you have kidney concerns.

Don't forget the rest of your nutrition

Eating less overall can make it harder to cover everything else your body needs. The UCL researchers highlighted protein, fibre, vitamins and minerals as nutrients people can fall short on without proper support. A few simple safeguards:

• Fibre: include vegetables, beans, oats and wholegrains; adults are advised to aim for 30 g a day.
• Fluids: reduced food intake also means less water from food, so keep a bottle with you.
• Vitamin D: UK guidance is for everyone to consider 10 micrograms a day in autumn and winter.
• Variety: smaller portions are fine, but keep them colourful and varied.

Sample day: protein on a small appetite

• Breakfast: 200 g Greek yoghurt with berries and a spoon of oats (about 20 g protein).
• Lunch: two-egg omelette with spinach and a slice of wholegrain toast (about 15 g).
• After training: one shake made with whey isolate and water (about 25 g).
• Dinner: a small salmon fillet with lentils and vegetables (about 30 g).

That is roughly 90 g of protein across four small eating occasions, which is far more manageable than three large plates.

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FAQs

Do weight-loss jabs make you lose muscle?

Any significant weight loss includes some lean mass. Studies cited by ukactive suggest 20–50% of weight lost on GLP-1 medication can be lean mass, which is why strength training and adequate protein are recommended.

How much protein should I eat on Wegovy or Mounjaro?

There is no single official figure for people on these medicines. Many experts suggest around 1.2–1.6 g per kg of body weight for active people who are losing weight. Ask your prescriber or a registered dietitian for personal advice.

Can I take creatine while on GLP-1 medication?

Creatine is widely used and well studied, but you should check with your prescriber or GP before adding any supplement while taking prescription medication.

What type of exercise is best to keep muscle?

Resistance training, such as weights, machines, bands or bodyweight exercises, at least twice a week, alongside regular moderate activity like brisk walking.

Are protein shakes necessary?

No. Food can cover your needs. Shakes are simply a convenient option when appetite is low or meals are small.

Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle.