Research

SURMOUNT trials overview: tirzepatide body-composition findings (2026 summary)

The SURMOUNT trial program established the efficacy of tirzepatide for chronic weight management. Body-composition substudy findings most relevant to nutritional planning.

The SURMOUNT (Studies of Tirzepatide in Obesity) trial program established the efficacy of subcutaneous tirzepatide for chronic weight management. This article summarizes the major SURMOUNT trials with a focus on the body-composition findings most relevant to nutritional planning.

SURMOUNT-1 (Jastreboff et al., NEJM 2022)

SURMOUNT-1 randomized 2,539 adults with obesity (or overweight with at least one weight-related comorbidity) without Type 2 diabetes to tirzepatide 5 mg, 10 mg, or 15 mg weekly versus placebo, all with lifestyle intervention, over 72 weeks. Mean weight loss in the 15 mg group was approximately 20.9% versus 3.1% in the placebo group; the 5 mg group achieved approximately 15.0% and the 10 mg group approximately 19.5%.

The magnitude of weight loss in SURMOUNT-1 (particularly at the 15 mg dose) is the largest reported in any pharmacotherapy trial for chronic weight management.

Body-composition substudy: a subset of participants underwent DXA at baseline and at week 72. Total body weight loss was distributed approximately as fat mass and lean mass in proportions consistent with rapid weight loss; the proportion of total weight loss attributable to lean tissue in published analyses clusters around 25-35% in this trial cohort, with substantial individual variability. The absolute lean-mass loss is larger than in STEP-1 because the absolute total weight loss is larger.

SURMOUNT-2 (Garvey et al., The Lancet 2023)

SURMOUNT-2 examined tirzepatide 10 mg and 15 mg weekly versus placebo in 938 adults with obesity (or overweight with comorbidities) and Type 2 diabetes over 72 weeks. Mean weight loss was approximately 12.8% (10 mg) and 14.7% (15 mg) versus 3.2% (placebo). The smaller magnitude versus SURMOUNT-1 is consistent with the broader observation that GLP-1 and GIP/GLP-1 weight loss is somewhat smaller in T2D populations at the same dose.

SURMOUNT-3 (Wadden et al., Nature Medicine 2023)

SURMOUNT-3 examined tirzepatide added to intensive lifestyle intervention (ILI) in patients who had completed an initial 12-week ILI lead-in. The study evaluated the additive effect of pharmacotherapy on top of an established lifestyle intervention. Patients receiving tirzepatide following the ILI lead-in achieved an additional approximately 18.4% weight loss over 72 weeks; the placebo arm experienced regain.

SURMOUNT-3 informs the discussion of pharmacotherapy as additive to (not replacing) lifestyle intervention.

SURMOUNT-4 and beyond

SURMOUNT-4 (Aronne et al., 2024) examined withdrawal versus continuation of tirzepatide after 36 weeks of open-label active treatment, providing data on regain risk after discontinuation. The withdrawal group regained substantial weight; the continuation group maintained losses. This is the most-cited evidence for the long-term-treatment framing of GLP-1 receptor agonist therapy for chronic weight management.

Body-composition findings across SURMOUNT

Across the SURMOUNT trial body-composition substudies, recurring observations:

• Total weight loss composed of both fat-mass and lean-mass loss, broadly similar in proportion to STEP findings (approximately 25-35% lean tissue).
• Absolute lean-mass loss is larger in SURMOUNT than STEP at equivalent durations because absolute total weight loss is larger.
• The relative magnitudes do not strongly differentiate tirzepatide from semaglutide on the lean-mass-loss-proportion dimension; the larger SURMOUNT weight loss is reflected in larger absolute (rather than larger proportional) lean-mass loss.

Differences from STEP

SURMOUNT differs from STEP in several practical ways relevant to nutritional planning:

• Larger magnitude of weight loss at full dose, particularly at 15 mg (SURMOUNT-1 ~20.9% vs STEP-1 ~14.9%).
• Longer titration schedule (more dose-escalation steps), producing more periodic side-effect peaks during initiation.
• Some patient-reported differences in side-effect pattern (variable across individuals).
• Possible mechanistic differences from the GIP component, though the practical nutritional implications are not yet differentiated from semaglutide in clinical guidance.

What the SURMOUNT findings inform for nutritional practice

The body-composition findings from SURMOUNT, like those from STEP, underpin the protein-and-resistance-training framework on this site. The larger absolute weight-loss magnitude in SURMOUNT (particularly at 15 mg tirzepatide) means the absolute pressure on protein adequacy and lean-mass preservation is greater than at equivalent semaglutide doses.

For patients on tirzepatide at full dose, the protein-target framework (1.2-1.6 g/kg LBM/day for adults with normal renal function; 1.4-1.8 for older adults) and the resistance-training framework (2-3 progressive sessions per week covering major muscle groups) are particularly consequential.

References

1. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine. 2022;387(3):205-216. (SURMOUNT-1.)
2. Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). The Lancet. 2023;402(10402):613-626.
3. Wadden TA, Chao AM, Machineni S, et al. Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity: the SURMOUNT-3 phase 3 trial. Nature Medicine. 2023;29(11):2909-2918.
4. Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: the SURMOUNT-4 randomized clinical trial. JAMA. 2024;331(1):38-48.
5. Holmstrup ME, Fairman CM, Calanna S, et al. Body composition during pharmacologic weight loss with GLP-1 receptor agonists. Obesity Reviews. 2025;26(4):e13721.