The increasing use of weight-loss injections, particularly glucagon-like peptide-1 (GLP-1) receptor agonists and related therapies, has transformed the management of obesity. By reducing appetite and energy intake, these medications can produce substantial weight loss, but they also raise important nutritional concerns. Reduced food intake may make it more difficult to meet requirements for protein, fiber, vitamins and minerals. A recent joint advisory from major nutrition and obesity organizations highlighted gastrointestinal side effects, nutritional deficiencies and loss of muscle and bone mass among the nutritional challenges that should be considered during GLP-1-based therapy¹.
One of the main concerns is the preservation of lean mass during rapid weight loss. Although fat mass generally accounts for most of the weight lost with incretin-based medications, a clinically relevant proportion may come from lean mass. A 2026 systematic review² and meta-analysis of 20 randomized controlled trials found that lean mass represented approximately 25-39% of total weight loss with incretin therapies, depending on the medication. The authors also found that combining weight-loss interventions with resistance training was associated with a more favorable preservation of lean mass². This has contributed to growing interest in adequate protein intake and resistance exercise as complementary strategies during pharmacological weight loss.
However, simply increasing protein consumption is not necessarily sufficient. When appetite is markedly suppressed, individuals may focus heavily on protein-rich foods or supplements while unintentionally reducing their intake of fruits, vegetables, whole grains and other sources of dietary fiber and micronutrients. Excessive reliance on protein supplements and highly processed protein products may also contribute to gastrointestinal discomfort, particularly in individuals already experiencing nausea, early satiety, bloating or constipation associated with GLP-1 therapy. Therefore, nutritional management should focus not only on achieving adequate protein intake but also on maintaining overall dietary quality and nutritional adequacy¹.
The growing use of weight-loss medications therefore brings a new nutritional challenge: achieving weight loss while preserving the quality of the weight lost. Current evidence supports an individualized approach that considers protein intake, dietary fiber, micronutrient adequacy, muscle function and physical activity rather than focusing exclusively on body weight³. Resistance training appears particularly relevant for maintaining muscle during weight reduction, while adequate protein can help support muscle protein synthesis¹,³. Ultimately, pharmacological treatment for obesity should ideally be accompanied by nutritional and lifestyle strategies that help patients maintain muscle mass, digestive health and overall nutritional quality throughout the weight-loss process.
References
1) Mozaffarian D, Agarwal M, Aggarwal M, Alexander L, Apovian CM, Bindlish S, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. Am J Clin Nutr. 2025;122(1):344–367. doi:10.1016/j.ajcnut.2025.04.023
2) Eisa N, Barood O. Lean Mass Changes With Incretin Therapy Versus Lifestyle Intervention: A Systematic Review and Meta-Analysis of Randomised Controlled Trials. Diabetes Obes Metab. 2026;28(6):4818–4827. doi:10.1111/dom.70666
3) Mechanick JI, Butsch WS, Christensen SM, Hamdy O, Li Z, Prado CM, Heymsfield SB. Strategies for minimizing muscle loss during use of incretin-mimetic drugs for treatment of obesity. Obes Rev. 2025;26(1). doi:10.1111/obr.13841
