- Global academic review from Les Mills and ukactive highlights crucial role of strength training and exercise for people on weight loss drugs to maintain muscle mass.
- Evidence shows 20 to 50 per cent of weight lost is lean body mass – posing significant health risks.
- Nearly 2.5 million people reported to be using weight loss drugs in the UK.
- Authors call for Government, pharmaceutical and nutrition sectors to work in partnership with health and fitness sector on a sustainable package of support.
The impact of weight loss drugs on skeletal muscle mass has been revealed in a new report by Les Mills and ukactive showing the importance of exercise and strength training for success.
Titled ‘GLP-1 medications and muscle mass preservation: Implications and recommendations for the health and fitness sector’, the report represents one of the first reviews of global academic evidence exploring how weight loss medications work, the side effects, and how to avoid the loss of lean body mass (skeletal muscle and bone mass) through exercise and strength training.
Led by Gillian L. Hatfield, PhD, Associate Professor at the University of the Fraser Valley, Canada, the review shows that loss of lean body mass is often an unintended consequence of taking GLP-1 or GLP-1/GIP receptor agonists (weight loss medications), with other side effects including constipation, nausea, and vomiting.
When substantial weight loss occurs through caloric restriction, whether through dieting, bariatric surgery, or GLP-1 and GLP-1/GIP receptor agonists, loss of muscle mass is an unwanted consequence, as high caloric deficits lead to the body breaking down skeletal muscle tissue for energy. The report notes the magnitude of lean body mass loss can be similar to that resulting from bariatric surgery, cancer treatment, or 10 years of ageing, stating: “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 shows that loss of muscle mass is particularly concerning for older adults due to the increasing risk of frailty and falls, which cost the NHS £2.3bn every year.
However, the studies within the review show that combining exercise – particularly strength training – with a healthy diet can help mitigate muscle loss. Other benefits included maintaining the amount of weight loss and minimising the overall muscle and bone loss found when taking the medications.
Research cited in the report found exercising while using weight loss medications helps maintain weight loss even after medication is discontinued – meaning weight regain could be minimised if supported by sustainable physical activity levels. Guidelines from the Chief Medical Officer recommend taking part in two-to-three strength training sessions a week and 150 minutes of moderate to vigorous physical activity a week. Guidance from the National Institute for Health and Care Excellence (NICE) goes even further and suggests that those who are prescribed medicines for weight management must receive wrap-around care focusing on diet, nutrition and increasing physical activity, including strength training, rather than using them as standalone treatments.
On a national scale, the report makes a series of recommendations to support users of weight loss medications, with the authors calling for the Government to urgently convene the nutrition sector and the health and fitness sector on the required wraparound support offered to GLP-1 patients, with commitment and investment from the pharmaceutical sector.
In October last year, the Health Secretary, Wes Streeting, announced the rollout of GLP-1 as a measure to address the severest forms of obesity across the UK and help get people back into work. Uptake of the medication has surged, with the UK weight loss market experiencing an average monthly volume growth of almost a quarter (24.6%) between October 2024 and March 2025, but Government efforts have focused on rollout rather than the essential lifestyle changes and post-treatment support that are vital for sustainable and positive outcomes.
The report provides practical recommendations for health and fitness organisations to support customers taking weight loss medications.
Sector recommendations:
- Actively review health offerings to ensure they best support users.
- Work proactively with the nutrition and obesity sector to forge partnerships that can support people taking weight loss medication.
- Increase workforce knowledge and understanding to support those taking weight loss medications, such as through specific training, considering consumer perceptions and up-to-date evidence of weight loss medication to understand its mechanisms, effectiveness, side effects, and how exercise can support users.
Dr Matthew Wade, Interim Director of Research at ukactive, said: “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.”
Bryce Hastings, Head of Research at Les Mills, said: “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.”
