Experts at ADA 2026 focus on muscle loss and nutrition for people taking semaglutide and tirzepatide

At the American Diabetes Association 2026 Scientific Sessions in June, four clinicians said care for people taking GLP-1 receptor agonists is expanding past weight and blood sugar into muscle preservation, nutrition and joint health. The symposium, "GLP-1 Receptor Agonists: What's New in 2026?", covered lean body mass, diet targets and osteoarthritis data ^[1].

Muscle loss and what clinicians are measuring

Ian Neeland, MD, director of cardiovascular prevention at University Hospitals Harrington Heart & Vascular Institute, said that as a rule of thumb roughly 25% of total weight lost through any intervention — diet, medication or surgery — comes from lean body mass, and that with newer, higher-dose GLP-1 compounds the proportion can climb to 40% or more ^[1]. He added that each kilogram of muscle mass lost reduces resting energy expenditure by 13 kilocalories, compared with 4 kilocalories for fat mass ^[1].

Neeland pointed to the S-LITE trial, in which combining liraglutide with supervised resistance and aerobic training produced greater weight loss and allowed patients to gain lean mass, an outcome not seen with medication alone ^[1]. For protein, he cited evidence supporting 1.2 to 1.6 grams per kilogram of body weight per day, with diminishing returns above that range ^[1]. In the phase 2 BELIEVE trial, semaglutide combined with the myostatin inhibitor bimagrumab reduced the lean-mass share of total weight loss from about 21% to 7% ^[1].

Neeland also flagged a gap: "I have not seen great large-scale trials looking at function of muscle," he said, adding that how muscle function is measured in the clinic is not clear ^[1].

Nutrition targets discussed

Patti Urbanski, a registered dietitian nutritionist and member of the ADA 2026 Nutrition Consensus Statement writing committee, described targets drawn from a 2025 obesity nutrition and lifestyle consensus report: protein at 1.5 grams per kilogram per day, fiber at 25 to 30 grams daily for women and 30 to 35 grams for men, fat at 25 to 60 grams per day on a lower-calorie diet, and at least 2 liters of water daily ^[1]. She said involving registered dietitian nutritionists can reduce GLP-1 discontinuation rates by as much as 5 to 10% in trials and likely more in practice, and recommended baseline screening for eating disorders, gastrointestinal conditions, kidney insufficiency, sarcopenia and social factors before giving dietary guidance ^[1].

Arthritis pain data and an open question

In the STEP 9 trial, semaglutide 2.4 mg given to people with knee osteoarthritis and a mean body mass index of 40.3 produced a mean weight change of 13.7% and a 41.7-point reduction in WOMAC pain scores, compared with 27.5 points in a structured-care comparison group. Use of pain medications, including opioids, fell significantly in the semaglutide group ^[1].

The trial had no post-study knee imaging, synovial fluid analysis or inflammatory biomarkers ^[1]. Topline results from the TRIUMPH 4 trial of tirzepatide showed roughly 23% weight loss produced pain reductions similar to semaglutide's 13%, raising the possibility that past about 10% weight loss, additional loss does not add proportionally greater joint benefit ^[1]. "We need to leave the door open for biological metabolic effects on top of the actual weight," said Sean Wharton, MD, PharmD, of the Wharton Medical Clinic in Toronto ^[1].

For context, the same session covered new formulations: oral semaglutide 25 mg produced 13.6% to 16.6% mean weight loss in OASIS 4, with 36% of participants losing at least 15%; orforglipron, the first small-molecule GLP-1, produced 7.5% to 11.2% across doses and requires dose adjustments with certain cytochrome P450 3A4 drugs; and semaglutide 7.2 mg produced 20.7% mean weight loss in STEP UP versus 17.5% at the standard 2.4 mg dose ^[1].

Why it matters for patients

Losing lean mass affects strength and daily function, and Neeland tied it to lower resting energy expenditure, which is one factor in maintaining weight loss over time ^[1]. The practical tools discussed — adequate protein and supervised resistance training — are the ones with trial data behind them so far, while myostatin inhibition is still in phase 2 testing ^[1]. Dietitian involvement was linked to lower rates of stopping GLP-1 treatment, which matters for people weighing whether to stay on a drug ^[1]. For knee osteoarthritis, the STEP 9 results show a pain benefit, but the trial did not measure joint structure or inflammation, so whether the drugs change the disease itself has not been established ^[1]. How to measure muscle function in routine care also has not been standardized, Neeland said ^[1].

What happens next

No dates for new muscle-function or joint-imaging trials were given. Wharton called for MRI data, synovial biopsies and biomarker analysis in future osteoarthritis trials to separate weight effects from other biological effects, and Neeland said large-scale trials of muscle function are still lacking ^[1].