Weight Loss Drugs Study Reveals Significant Muscle Loss Differences
A comprehensive new study has examined the comparative effects of two leading weight-loss medications, revealing that Eli Lilly's tirzepatide results in greater overall weight reduction but at a higher cost to muscle and connective tissues than Novo Nordisk's semaglutide. The research, published ahead of peer review this week, analysed data from approximately 1,800 patients using tirzepatide and 6,200 using semaglutide.
Muscle Mass Reduction Findings
The analysis conducted by Massachusetts-based data analytics firm nference found that tirzepatide was consistently linked to more significant lean body mass loss compared to semaglutide. Patients on tirzepatide experienced an average of 1.1 per cent more lean body mass reduction after three months, escalating to 2 per cent after twelve months of continuous use.
"This suggests that patients shouldn't simplistically be thinking, 'I want to lose X amount of weight and I'll go with the option that delivers greater weight loss,'" said study leader Venky Soundararajan of nference regarding the data published online.
Treatment Monitoring and Methodology
Patients were tracked before and during treatment using either low-radiation scans or "smart" scales that estimate body fat percentage, muscle mass, bone mass, and other components. The study cannot explain why lean body mass loss was greater with tirzepatide, which mimics both GLP-1 and GIP hormones, compared with semaglutide, which only mimics GLP-1. These hormone-mimicking mechanisms slow digestion and create feelings of fullness.
Pharmaceutical Company Responses
A Novo Nordisk spokesperson did not comment directly on the current study but noted that changes in muscle mass did not significantly differ between semaglutide and placebo groups in clinical trials, with physical function being preserved. Meanwhile, a Lilly spokesperson stated that fat loss achieved through healthy dieting is similarly accompanied by lean body mass reduction.
In its late-stage clinical trial, "the ratio of fat-mass loss to lean-mass loss for patients treated with tirzepatide was generally consistent with that reported in lifestyle-based treatments for obesity," the Lilly spokesperson explained.
Critical Statistics and Risk Factors
Approximately 10% of tirzepatide users who lost more than 20% of their total body weight were found to have lost more than 5% of their lean body mass. This was true for fewer than 7% of semaglutide users who achieved the same percentage of body weight reduction.
Decreased exercise tolerance during treatment was linked with greater lean body mass loss in both groups, but to a more significant extent in tirzepatide-treated patients. Higher doses, longer treatment duration, and pre-existing musculoskeletal pain before treatment began were also associated with greater lean body mass decline with both medications.
The Exercise Imperative
Researchers emphasised that exercise during treatment is essential with both drugs to mitigate muscle loss. "It's a vicious cycle," Soundararajan explained. "If you start with a drug which puts you at a greater probability of lean body mass loss... and you have a preexisting history of musculoskeletal diseases, it puts you at greater risk of lower tolerance to exercise. And if you're not exercising when you're on these medicines, you are essentially causing attrition of lean body mass."
Both tirzepatide and semaglutide have surged in popularity for their efficacy in weight management and have demonstrated additional health benefits, including protective effects on cardiovascular health. Despite their success, concerns have persisted regarding their potential to induce loss of muscle and other lean body mass components alongside fat reduction.
