The short answer
In a semaglutide study, lean tissue became a larger share of body weight even though its measured amount fell.
What did researchers measure?
A SUSTAIN 8 substudy followed 178 adults with type 2 diabetes taking metformin. They received weekly semaglutide 1 mg or daily canagliflozin 300 mg for 52 weeks.
Lean tissue includes muscle, but also organs, connective tissue and water.
Different measures; kilograms and percentage points are not the same scale
Lean tissue amount
Fell in both treatment groups
Lean tissue share
Rose in both treatment groups
Strength
Not measured by these scans
Original visual based on the study.
| Group or measure | Result |
|---|---|
| Lean tissue amount | Fell in both treatment groups |
| Lean tissue share | Rose in both treatment groups |
| Strength | Not measured by these scans |
What changed?
Estimated fat loss was 3.4 kg with semaglutide versus 2.6 kg with canagliflozin. Lean-tissue loss was 2.3 kg versus 1.5 kg. Neither comparison showed a clear difference between treatments.
Yet lean tissue’s share rose by 1.2 versus 1.1 percentage points. A percentage can rise when the overall total shrinks.
How much can this tell us?
Only 114 participants had follow-up scans that qualified for the main analysis; missing values were estimated. An analysis using more available scans gave similar findings.
There was no placebo group. Scans could not isolate muscle loss or establish changes in strength.
The takeaway: check whether a “muscle” claim describes kilograms, percentages, or actual strength.
Novo Nordisk funded and helped conduct the study.