Andy Devaney
GLP-1 has taken the weight-loss world by storm, but a new global review suggests all that rapid shrinking might come with a price people aren’t expecting: lost muscle. And not the “one-rest-day-too-many” kind — we’re talking 20 to 50 per cent of total weight lost coming straight from lean body mass.
It’s the sort of finding that stops even seasoned trainers mid-rep. Les Mills and ukactive have pulled together one of the most comprehensive assessments yet of how weight-loss medications affect the body, and the message is blunt: without proper exercise — especially strength work — GLP-1 users risk weakening the very foundation that keeps them moving.
Titled ‘GLP-1 medications and muscle mass preservation: Implications and recommendations for the health and fitness sector’, the report lands just as nearly 2.5 million people in the UK are believed to be using weight-loss drugs. Demand is soaring. Guidance, however, is lagging far behind.
A Clear Warning: Muscle Loss Isn’t a Side Note — It’s a Threat
Led by Dr Gillian L. Hatfield, Associate Professor at the University of the Fraser Valley, the review confirms what many trainers have suspected: significant weight loss triggered by GLP-1 or GLP-1/GIP receptor agonists almost always carries unwanted consequences. One of them is lean mass loss — skeletal muscle and bone that most of us spend years trying to protect.
Constipation, nausea and vomiting are on the typical side-effect list. But the big issue is deeper: “The loss of lean body mass (muscle and bone) associated with GLP-1 receptor agonists can have a significant negative impact on long-term health.”
The review compares the scale of muscle depletion to what’s seen after bariatric surgery, cancer treatment, or even a decade of ageing. For older adults already on the brink of frailty, that’s a dangerous slide. Falls currently cost the NHS £2.3bn every year — without the added complication of medication-driven muscle wastage.
Strength Training: The Missing Half of the GLP-1 Story
Thankfully, the fix is straightforward. When users combine weight-loss medication with exercise — particularly strength training — the risks drop dramatically. Not only does it protect muscle, it also helps maintain fat loss long after treatment stops.
The Chief Medical Officer’s guidance is clear: two to three strength workouts a week, plus 150 minutes of moderate to vigorous activity. NICE pushes it further, insisting weight-loss drugs should never be a stand-alone solution, but part of a wraparound plan that includes diet, nutrition and physical activity.
The report drives this home: lifestyle support isn’t optional. It’s essential.
Government Rollout Races Ahead — Support Lags
Last October, Health Secretary Wes Streeting announced a nationwide rollout of GLP-1 to tackle severe obesity and boost workforce participation. Since then, the weight-loss market has grown by almost 25% each month. Momentum isn’t the issue — but the safety net underneath certainly is.
The report calls for the Government to bring fitness, nutrition and pharmaceutical leaders together to build proper support for GLP-1 users. Without it, even the best-intentioned rollout risks leaving millions weaker than when they started.
Sector Told to Step Up: What Gyms and Trainers Must Do Now
The report outlines practical steps for the health and fitness industry:
- Review current programmes to ensure they genuinely support people on weight-loss medications.
- Build stronger partnerships with nutrition and obesity experts.
- Train staff to understand how GLP-1 works, what the side effects are, and how to programme strength-focused sessions that protect users.
Voices From the Front Line
Dr Matthew Wade, Interim Director of Research at ukactive, doesn’t mince his words: “Millions of people are taking weight loss medications across the UK but this evidence shows the risks of ignoring strength training and exercise during treatment.
“The rapid rollout of GLP-1 has shown dramatic results for patients but in order to avoid weakening the body, there are simple and effective strength exercises which are essential for sustainable results.
“The health and fitness sector can support people taking weight loss medications, but we want to see the Government go further by working with the fitness, nutrition and pharmaceutical industries to deliver the critical wraparound support patients need.”
Les Mills’ Head of Research, Bryce Hastings, reinforced that message: “Regular strength training is vital to our health at all stages of life, but the research suggests this is especially true for people taking weight loss medications.
“In addition to strength training two to three times a week, it’s recommended that people taking weight loss medications accumulate 150 minutes of moderate to vigorous physical activity per week. Studies have shown this helps continue fat mass loss in the weight maintenance phase of treatment and lessen weight regain after treatment has stopped.
“More research is needed to deeper understand the relationship between weight loss medications and strength training, but the evidence and recommendations in our report are the start of the journey and offer practical next steps to better support the growing number of people taking weight loss medication.”
The Takeaway
GLP-1 medication can help people lose weight at speed — no one disputes that. But without resistance training stitched into the routine, users risk trading fat loss for a weaker body. This review makes one thing clear: medication alone isn’t a solution. Muscle is non-negotiable.
To read the full report, GLP-1 medications and muscle mass preservation: Implications and recommendations for the health and fitness sector, click here.
