The impact of weight loss drugs on skeletal muscle mass and the importance of exercise and strength training has been revealed in a new report from Les Mills and UK Active. 

GLP-1 medications and muscle mass preservation: Implications and recommendations for the health and fitness sector is 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 through exercise and strength training.  

Led by Gillian Hatfield, 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 weight loss medications. High caloric deficits lead to the body breaking down skeletal muscle tissue for energy and can have a significant impact on long-term health.

One paper reviewed in the study (Incretin-Based Weight Loss Pharmacotherapy: Can Resistance Exercise Optimize Changes in Body Composition?) found that over a 68-78 week period, GLP-1 use led to a decrease of between 6.0 and 6.9 kg of lean muscle mass, or the equivalent of "a decade or more or human ageing," with this accelerated ageing likely to be a critical issue for consumers.

The review shows that loss of muscle mass is particularly concerning for older adults due to the increasing risk of frailty and falls, which costs the NHS in the UK £2.3 billion every year, for example. 

Combining exercise – particularly strength training – with a healthy diet can help mitigate muscle loss. This also has the added benefit of maintaining the amount of weight loss and minimising the overall muscle and bone loss found when taking the medications. Exercising while using weight loss medications also helps to maintain weight loss after medication is discontinued by embedding better lifestyle habits. 

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 goes even further and suggests that those who are prescribed medicines for weight management must receive wraparound care focusing on diet, nutrition and increasing physical activity, including strength training, rather than using them as standalone treatments. 

Uptake of the medication has surged in the UK, with the UK weight loss market experiencing an average monthly volume growth of 24.6 per cent between October 2024 and March 2025. However, government efforts have focused on rollout rather than the essential lifestyle changes.

The report authors are calling for the UK 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. 

Fitness professionals are given a number of practical recommendations in the report to support customers taking the drugs, including working proactively with the nutrition and obesity sector, upskilling the workforce and keeping abreast of up-to-date evidence.

Dr Matthew Wade, interim director of research at UK Active, says: “The rapid rollout of GLP-1s has shown dramatic results for patients but in order to avoid weakening the body, there are simple and effective strength exercises that 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, says: “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 (two and a half hours) 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.” 

To read the report, GLP-1 medications and muscle mass preservation: Implications and recommendations for the health and fitness sector, click here.

Last week the World Health Organization released its first guidelines on the use of GLP-1s. It said that medication alone will not solve the problem but a supportive approach is needed including societal change and counselling on behavioural and lifestyle changes.

WHO also endorsed GLP-1s for longer-term use – a change from the original advice that the drugs should only be used for three to six months.