Obesity Treatment Should Be Judged by Health Gains, Not Weight Loss

Percent total body weight loss, the end point that governs regulatory approval of obesity drugs, is a poor measure of whether treatment is actually improving health, according to a scientific statement released September 9 by the Endocrine Society.¹

The statement addresses trial design and research priorities rather than coverage policy. Utilization management for obesity medications commonly relies on weight-loss thresholds, and a change in how efficacy is defined in trials would raise the question of what those criteria should measure instead.

The statement, published in Endocrine Reviews, sets out 6 research priority areas: obesity pathophysiology and the regulation of defended fat mass, heterogeneity in treatment response, redefining treatment targets beyond percent total body weight loss, the physiology of treatment response phases, health outcomes with pharmacotherapy, and long-term safety. The authors state the document is not intended as treatment guidance.

Why Percent Weight Loss Falls Short as an End Point

Mean percent weight reduction from baseline remains the primary efficacy end point under FDA guidance, and a draft guidance circulated in January 2025 left that standard essentially unchanged.^1,2 The authors argue the measure served adequately when interventions produced modest weight loss but no longer does.¹

Averaging obscures wide interindividual variation, and identical percentages carry different clinical meaning depending on starting body mass index (BMI). Patients beginning at a lower BMI reach a healthy weight with smaller reductions, and for those with a BMI below 30 kg/m², exceeding 20% weight loss can produce undesirable and unhealthy BMI levels.

In place of relative change, the authors propose defined targets tied to outcomes, analogous to a hemoglobin A1c goal below 6.5% in diabetes. They point to work reported at the 2024 European Obesity Congress, in which a postreduction BMI of 27 kg/m² and/or a waist-to-height ratio at or below 0.53 indicated a low 10-year absolute risk of type 2 diabetes, hypertension, hip or knee osteoarthritis, and atherosclerotic cardiovascular disease. A subsequent analysis of more than 280,000 primary care patients by the same group found that combining anthropometric and biomarker inputs could further personalize those targets.^1,3

Benefit Thresholds Vary by Complication

Weight reduction of only 2% to 5% can improve glycemia and lower triglycerides.¹ Quality of life, mobility, and depression measures show graded improvement beginning at 5% to 10%, a range also associated with reduced health care costs. Obstructive sleep apnea and knee osteoarthritis, both tied to the mechanical burden of excess fat, generally require 10% to 15%.

Several trials produced health benefits disproportionate to the weight lost. In SELECT (NCT03574597), mean weight reduction was under 10%, compared with roughly 15% in STEP 1 (NCT03548935), yet semaglutide reduced major adverse cardiovascular events by 20% and all-cause mortality by 19%.^1,4 Prespecified analyses attributed about one-third of the risk reduction to decreased waist circumference, and event curves separated before substantial weight loss occurred.¹

The authors read that gap between weight lost and benefit gained as evidence of disease-modifying effects independent of weight reduction. It also raises whether sustaining those benefits requires continued drug exposure rather than merely a maintained lower weight.

Lean Mass Loss Tracks Weight Loss, Not Drug Class

Addressing a frequent clinical worry, the statement cites a 2026 meta-analysis of 20 randomized trials and 15,782 participants using dual-energy X-ray absorptiometry (DXA) or MRI body composition.⁵ Lean mass accounted for approximately 26% of total weight loss, with no significant difference between glucagon-like peptide-1 (GLP-1) receptor agonist therapy and intensive lifestyle intervention (roughly 30% vs 26%; P = .42). Strength, mobility, and fracture outcomes in older adults remain inadequately studied.

Registration trials are too short, too small, and too narrowly enrolled to characterize rare adverse events or real-world effectiveness, the authors write.¹ They urge that observational analyses be designed within a target trial emulation framework using active-comparator, new-user designs, with priority on persistence, pregnancy exposure, compounded products, and lower-dose prescribing.

Disclosures across the writing group are extensive. Most authors report consulting, advisory, or research relationships with manufacturers of the drugs the statement discusses, including Eli Lilly and Novo Nordisk.

References

1. Jastreboff AM, Ard JD, Hall KD, et al. Obesity science, research gaps, and opportunities in the new era of obesity medicines: an Endocrine Society scientific statement. Endocr Rev. Published online September 9, 2026. doi:10.1210/endrev/bnag025

2. Obesity and overweight: developing drugs and biological products for weight reduction. Draft guidance. US Food and Drug Administration; January 2025. Accessed September 18, 2026. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/obesity-and-overweight-developing-drugs-and-biological-products-weight-reduction

3. Busetto L, Schnecke V, Overvad M, et al. The identification of potential treatment targets to reduce the risk of obesity-related complications: a step toward a treat-to-target approach in obesity management. Obes Sci Pract. 2025;11(6):e70094. doi:10.1002/osp4.70094

4. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221-2232. doi:10.1056/NEJMoa2307563

5. 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