Jump to: Understanding lean mass loss | What the research tells us | How to prevent muscle loss | Take home message
According to data from randomised controlled trials, you do lose some muscle mass (or lean mass) alongside fat when on Mounjaro.
However, losing some lean mass during weight loss is normal and expected. Plus, preventing excessive lean mass loss during weight loss can be achieved by eating enough protein, eating enough calories, strength training, and sleeping well.
Still, a systematic review of studies examining Mounjaro’s effects on body composition found that for every 1kg of lean mass lost, participants lost between 2.9-6.1kg of fat mass.
This indicates that while some lean mass loss occurs, the medication primarily targets fat tissue.
This finding has led some healthcare professionals to question whether weight loss from Mounjaro is ‘healthy.’
However, looking at these numbers in isolation oversimplifies the complex weight loss process and how our bodies adapt during this journey.
What happens when we lose weight
When we lose weight, our bodies don’t just lose fat tissue. We also lose some lean mass – but this isn’t necessarily a bad thing, nor does it always mean we’re losing muscle.
Lean mass includes everything in our body that isn’t fat tissue. This means it includes:
- Muscle tissue
- Bone
- Organs
- Water
- Other non-fat tissues
Importantly, even our fat cells contain some lean tissue in the form of water and supporting structures.
When we lose fat cells during weight loss, we also lose these lean components, which accounts for some of the lean mass loss seen in studies.
One study compared the impact of three different exercise and diet interventions on weight loss and lean mass.
The study showed that all three groups lost an average weight loss of 9kg, and their lean mass decreased by 2.7kg.
However, when the researchers accounted for the amount of lean tissue lost from adipose tissue, they found that the participants increased their total lean mass from other tissues by 0.3kg.
This effect has been replicated by other researchers who found a similar relationship between the loss of non-fat lean tissue from our adipose tissue during weight loss.
So, while a reduction in lean mass can occur when on Mounjaro, it may be only a small percentage of the lean tissue we care about: our muscle and bone.
Muscle loss on Mounjaro
Research investigating lean mass loss while on Mounjaro is limited, but some research published in 2024 suggests that tirzepatide (the drug in Mounjaro) may lead to an average loss of lean mass of around 11%.
The SURMOUNT-1 trial, which studied tirzepatide in people living with obesity without diabetes, found that participants experienced:
- A 33.9% reduction in fat mass
- A 10.9% reduction in lean mass
While this might seem concerning at first glance, it’s essential to understand that some lean mass loss during significant weight loss is normal and expected. The key is that the ratio of fat loss to lean mass loss strongly favours fat loss.
In people with type 2 diabetes, studies showed that participants lost between 2.9-6.1kg of fat mass for every kilogram of lean mass lost. This suggests that the primary weight loss while on Mounjaro comes from fat.
How to prevent muscle loss on Mounjaro
While some lean mass loss during weight loss is normal, here are 4 evidence-based strategies you can use to help preserve muscle mass while taking Mounjaro:
1. Lose weight slowly
- Avoid extremely low-calorie diets that go below a 25% calorie deficit. Ideally, a calorie deficit of 10-25% will help achieve sustainable weight loss without compromising lean mass.
- Focus on nutrient-dense whole foods and eat snacks in between meals if you’re losing weight too quickly
- We want to aim for weight loss of around 0.5-2lbs a week
2. Prioritise protein intake
- Aim for 20-40 grams of protein at each main meal
- Include protein sources like Greek yoghurt, eggs, fish, lean meat, tofu, or tempeh
- Consider spreading your protein intake throughout the day rather than having it all at once
- If you’re struggling to eat enough protein, consider an unsweetened protein powder with your breakfast and dinner
3. Incorporate strength training
- Aim for at least 2 resistance training sessions per week
- Focus on compound exercises that work multiple muscle groups
- Start with bodyweight exercises if you’re new to strength training
4. Get adequate sleep
- Aim for 7-9 hours of quality sleep each night
- Maintain a consistent sleep schedule
- Create a relaxing bedtime routine
- Avoid screens before bedtime
Take home message
While Mounjaro does lead to some lean mass loss during weight loss, this is normal and expected. The research shows that the medication primarily targets fat mass, with a favourable ratio of fat loss to lean mass loss.
By implementing strategies like adequate protein intake, strength training, appropriate calorie intake, and good sleep habits, you can help minimise muscle loss while taking Mounjaro.
Remember that everyone’s journey is different; what works best for you may require trial and error. Always work with your healthcare provider to develop an appropriate approach for your individual needs.
Second Nature’s medication programmes
Second Nature has two medication-supported programmes: a Wegovy weight-loss programme and a Mounjaro weight-loss programme.
Why should you choose Second Nature over other medication providers if you’ve decided to try Mounjaro or Wegovy (assuming you’re eligible)?
For peace of mind.
Second Nature has worked with the NHS for over 6 years, providing weight-loss programmes across the UK.
While our Wegovy and Mounjaro weight-loss programmes are private and not currently used by the NHS, we’ve built the programmes focusing on scientific evidence, patient safety, and data security.
We hope that our 6+ years of working with the NHS and building a track record of effective weight-loss results will give you peace of mind to give us a try.
