Semaglutide
Extensive weight-loss evidence with direct evidence of both fat loss and absolute lean-mass loss.
Signal summary
Semaglutide is one of the best examples of why percentages can mislead. Lean mass can become a larger percentage of body weight while absolute lean mass still falls.
Study details
Doses studied — not a dosing recommendation. Regimens belong to the named study, formulation and population.
STEP 1 exploratory DXA analysis
- Population
- 140 adults from the STEP 1 obesity trial without diabetes.
- Doses and administration studied
- 2.4 mg subcutaneously once weekly, following escalation, versus placebo.
- Duration
- 68 weeks
- Reported finding / status
- Reported changes included fat mass -19.3% and lean mass -9.7% with semaglutide.
- Interpretation and limitations
- The cited report is a conference-supplement abstract. These body-composition findings do not establish outcomes with oral semaglutide or 7.2 mg injection.
Source tier B — conference abstract · Read the original study or record
Outcome Evidence Strength
Weight: mature obesity RCT evidence. Fat and lean: this card relies on an exploratory conference abstract. Function: not established by that analysis.
Formulation matters
The current Wegovy label includes oral tablets and a 7.2 mg injection strength. These are separate from the 2.4 mg STEP 1 regimen above. Trial-specific body-composition findings should not be transferred between formulations.
Current prescribing information · Read the head-to-head comparison
What is actually established?
- In the STEP 1 body-composition substudy, body weight decreased 15.0% over 68 weeks.
- Total fat mass decreased 19.3% and regional visceral fat mass decreased 27.4%.
- Total lean body mass decreased 9.7%, while lean mass increased as a proportion of total body mass.
What is not established?
- Lean-body-mass change does not directly quantify contractile skeletal muscle.
- Composition data do not by themselves establish strength or physical-function outcomes.
- Different trials and populations should not be compared as if they were head-to-head.
Still being studied
How composition changes vary across populations and how lean-mass quantity relates to skeletal muscle quality, strength and long-term function.
Best human evidence at a glance
| Evidence | Population | Comparator & duration | Outcome measured | Evidence state |
|---|---|---|---|---|
| STEP 1 exploratory body-composition analysis | 140 adults with overweight or obesity in the STEP 1 DXA substudy | Placebo · 68 weeks | Scale weight, total fat mass, visceral fat and total lean body mass | Peer-reviewed Exploratory DXA analysis rather than a direct muscle-function trial. |
Safety evidence context
Clinical and regulatory safety evidence is mature for approved indications. Consult the current official label and a qualified clinician for risks, contraindications and individual decisions.
Interpretation boundary
This card describes population-level evidence and does not recommend a therapy, dose or protocol.
What changed: Added the RecompSignal Evidence Maturity distinction, study-design context and an explicit DXA limitation.
Semaglutide vs Tirzepatide: compare the evidence layers.
Mechanism, trial design, scale weight and composition outcomes are shown separately.
Open the comparisonEvidence sources
Impact of Semaglutide on Body Composition in Adults With Overweight or Obesity
Wegovy approval history, labels and reviews