A new joint report from Les Mills and ukactive is raising concerns about the impact of popular weight-loss drugs on skeletal muscle mass, urging the UK Government and health sectors to integrate structured exercise—and especially strength training—into patient care plans. The publication, “GLP-1 medications and muscle mass preservation: Implications and recommendations for the health and fitness sector,” is among the first major reviews to synthesize global academic evidence on how GLP-1 and GLP-1/GIP receptor agonists affect body composition.

The review, led by Dr. Gillian L. Hatfield, Associate Professor at the University of the Fraser Valley in Canada, highlights that 20% to 50% of total weight lost while using GLP-1 medications may come from lean body mass, including both muscle and bone. Authors warn that, “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 report notes parallels between this unintended muscle loss and declines seen in bariatric surgery, cancer treatment, or a decade of aging.

With nearly 2.5 million people in the UK reported to be using weight-loss medications, the findings carry significant public health implications. Loss of muscle mass is particularly concerning for older adults due to increased risks of frailty and falls, which currently cost the NHS an estimated £2.3 billion annually.

However, the evidence also points to solutions. Studies in the review show that combining weight-loss medication with exercise—especially strength training—alongside balanced nutrition can reduce muscle loss, help maintain weight loss after medication stops, and improve long-term health outcomes. UK guidelines already recommend two to three weekly strength sessions and at least 150 minutes of moderate to vigorous activity. Guidance from NICE similarly states that weight-management prescriptions must include “wrap-around care” that addresses diet, nutrition, and physical activity, rather than medication alone.

As uptake of GLP-1 drugs continues to surge—growing nearly 25% per month between October 2024 and March 2025—ukactive and Les Mills are calling for coordinated action. Authors urge Government to convene the fitness, nutrition, and pharmaceutical sectors to build sustainable support systems for users. This follows last year’s announcement by the UK Health Secretary, Wes Streeting, outlining GLP-1 rollout as part of national obesity strategy, though critics note that implementation has focused more on access than on complementary lifestyle interventions.

The report also outlines sector-level recommendations, including reviewing health offerings, forging partnerships across nutrition and obesity care, and improving workforce training to better support medication 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, added: “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.”

FitBizWeekly will continue monitoring emerging research as GLP-1 medications reshape both healthcare and the fitness sector, with strength training increasingly recognized as a critical safeguard for long-term health.