Mounjaro (Tirzepatide) can be a highly effective treatment for weight loss. It works by reducing appetite and improving blood glucose control, often leading to significant weight loss over time.
However, when we lose weight, we don’t only lose fat. Some loss of muscle (or lean mass) is expected as part of the process. That’s normal, but if too much muscle is lost, it can affect your strength, energy levels, metabolism, and long-term health.
If you’re wondering ‘does Mounjaro cause muscle loss?’ the good news is excessive muscle loss is preventable. With the right approach to food, movement, and recovery, you can protect your muscle while continuing to lose weight safely and effectively.
Why muscle loss happens on Mounjaro
Mounjaro helps people reduce their calorie intake by lowering appetite. As the body loses weight, it draws on its energy stores — both fat and muscle. While the aim is always to lose fat, a small amount of muscle loss usually happens alongside it.
Certain factors can increase the amount of muscle lost:
- Eating too little, especially protein: Low appetite may lead to meals that lack the building blocks your muscles need.
- Rapid weight loss: The faster the weight drops, the higher the risk that your body pulls from muscle tissue as well as fat.
- Lack of resistance training: Muscles need to be “used” regularly to stay strong. Without stimulation from resistance training, they start to break down.
- Ageing or low starting muscle mass: We naturally begin losing muscle from our 30s onwards, and those with lower baseline strength may lose more if not proactive.
- Poor sleep or recovery: Inadequate rest and high stress levels affect hormones that influence muscle maintenance and repair.
These risks are manageable — especially when you know what to focus on.
How to keep your muscle while losing fat
While it’s unrealistic to expect zero muscle loss during weight loss, the goal is to keep it to a minimum. Below are five evidence-based strategies that can help you stay strong and preserve muscle while on Mounjaro.
1. Eat enough protein — and spread it out
Protein helps protect muscle when your body is in a calorie deficit. It provides the amino acids needed to maintain and repair muscle tissue.
- Aim for at least 60-75 grams of protein per day.
- Spread your intake across the day — aim for 20–30g of protein per meal.
- Prioritise protein sources such as lean meats, dairy, eggs, fish, tofu, lentils, beans as well as low fat dairy or soya alternatives.
- If you struggle to meet your target, a protein shake can help — especially after workouts.
- Include protein near exercise sessions to support recovery.
Even with reduced appetite, keeping protein intake consistent can significantly reduce muscle loss.
2. Commit to resistance training
Resistance training is the most effective way to signal to your body: “This muscle is still needed.” It helps preserve lean mass during weight loss and supports strength, bone health, and mobility.
- The NHS recommends strength-based exercise at least twice per week.
- Resistance training can include bodyweight exercises (like squats, lunges, or press-ups), free weights, resistance bands, gym machines, or even Pilates.
- Focus on compound movements that target multiple muscle groups, such as squats, rows, push-ups, deadlifts, and presses.
- Progress gradually over time. By adding resistance, increasing reps or sets, or shortening rest periods.
- Allow each muscle group 48–72 hours of recovery between sessions for optimal results.
You don’t need to go to the gym every day. What matters most is consistency, good form, and progressive challenge.
3. Don’t cut calories too aggressively
A calorie deficit is necessary for fat loss but going too low increases the risk of losing more muscle than necessary.
- Aim for a moderate deficit (250–500 calories below your maintenance needs).
- Include enough carbohydrates to support energy, especially for exercise.
- Include healthy fats (e.g. olive oil, avocado, nuts, seeds, oily fish) to support hormones and recovery.
- Stay well-hydrated, aim for at least 2-3 litres of fluid a day. Dehydration can impair muscle function.
Going slower with your weight loss may help you preserve more muscle long-term.
4. Work with your medication, not against it
Mounjaro reduces appetite which is helpful for weight loss, but it can also make it harder to meet your nutritional needs.
- If you notice significant strength loss or fatigue, speak to Phlo Clinic. Your dose or approach may need adjusting.
- If your appetite is low, prioritise protein and calorie-dense foods at times of day when eating feels easier.
- Track your progress in more than just scale weight. Consider measurements, clothing fit, or body composition measurements to see changes in fat vs. muscle.
Fat loss is the goal, not just weight loss. Focus on what you're losing.
5. Prioritise recovery
Muscle maintenance doesn’t just happen in the gym, it happens while you recover.
- Aim for 7–9 hours of sleep each night to support hormone regulation and muscle repair.
- Manage stress using whatever works for you — walks, stretching, journaling, or breathwork can help reduce cortisol levels.
- Include active recovery days with light movement like yoga or walking.
- Even if your hunger is reduced, don’t skip meals. Staying consistent with your intake supports recovery.
Recovery isn’t optional, it’s essential.
When using Mounjaro, some degree of muscle loss is part of the natural process of losing weight. But with the right strategy, you can minimise it, feel stronger, and support your long-term health.
Here’s your muscle-preserving plan:
- Eat enough protein every day
- Train with resistance twice per week
- Avoid extreme dieting
- Sleep, recover, and manage stress
- Track more than just your scale weight
If you're concerned about muscle loss or need help optimising your nutrition while on Mounjaro, you can get in touch with Phlo Clinic. We offer dietary support through practical Guides and ‘Phlo Nourish’ - our Behaviour Change Course designed to help you stay strong and healthy throughout your weight loss journey.
