New drugs for weight loss: Why change in body composition matters and why nutrition and exercise remain paramount.

Canadian family physician Medecin de famille canadien2025PMID: 41285626

View on PubMed DOI: 10.46747/cfp.711112705

Plain Language Summary

Clinical review for primary care physicians on appropriate patient selection for semaglutide and tirzepatide, emphasizing that changes in body composition matter beyond scale weight—specifically the risk of lean mass loss—and that proactive nutrition and resistance exercise interventions are essential adjuncts to pharmacotherapy. Uses GRADE evidence assessment. Provides evidence-based guidance for prescribers on integrating nutrition and exercise protocols with tirzepatide to minimize muscle loss—addressing the critical clinical gap between prescribing an anti-obesity medication and ensuring patients preserve functional lean tissue during pharmacologically driven weight reduction.

Abstract

OBJECTIVE: To identify patients who may or may not benefit from use of new drugs for weight loss and to aid in minimizing loss of lean mass through proactive nutrition and exercise interventions. QUALITY OF EVIDENCE: Choices and interventions are evaluated using the Grading of Recommendations Assessment, Development and Evaluation framework. Quality varies widely and is documented in multiple tables. MAIN MESSAGE: Semaglutide and tirzepatide should be used in patients living with obesity or with overweight accompanied by weight-related comorbidity. Long-term use may be necessary. Use in children and adolescents has proven effective for weight reduction, but long-term consequences are unknown. Use in elderly patients may be harmful. Because weight loss by any means is accompanied by loss of lean mass, specifically muscle and bone, particular attention must be paid to nutrition and exercise. Protein supplementation is effective to preserve muscle mass. Resistance training is effective in mitigation of both muscle and bone loss. Both resistance and aerobic training are beneficial in preventing osteopenia in weight loss, which may contribute to premature mortality. There is observational evidence that weight cycling may be harmful in that weight regain can be composed primarily of fat, multiple cycles of which may actually increase obesity in individuals. This is of particular concern because of the cost and limited availability of new weight loss drugs leading to large rates of discontinuation. Similarly, patients using drugs for small amounts of weight loss are likely to regain or overshoot if they discontinue. CONCLUSION: Patient selection for use of new anti-obesity drugs should match those included in clinical trials and be paired with dietary and exercise interventions used in those trials. Use at the extremes of age is problematic because of lack of long-term data. Intermittent use for small amounts of weight loss may be harmful. More ongoing data are needed.

Authors

Bosomworth, N John