Semaglutide studies show kidney and heart changes beyond weight loss

The trial used magnetic resonance imaging, or MRI, a scanner that can measure oxygen levels, blood flow, and inflammation in tissue. The three primary MRI measures were kidney oxygenation, overall blood flow, and tissue inflammation ¹. None of these changed significantly with semaglutide compared with placebo ¹.

But the study found changes in secondary measures. Blood flow resistance in the kidney's arteries fell significantly on semaglutide ¹. A separate MRI measure called apparent diffusion coefficient stabilized, which the authors interpret as prevention of fibrosis progression, meaning less buildup of scar tissue ¹. Cells in the kidney's filtering units also showed molecular changes, and spatial analyses found fewer immune cells close to those endothelial cells, the cells lining the tiny filters ¹. The authors suggest these mechanisms may include relaxed kidney blood vessels, less scarring, and healthier endothelial cells ¹.

Two animal models of heart failure with preserved ejection fraction, a form where the heart pumps normally but is too stiff to fill well, were used ². One was male ZSF1 obese rats; the other was female Göttingen minipigs with an induced form of the condition ². The animals were given semaglutide at doses chosen not to cause weight loss ².

In the rats, semaglutide reduced pressure inside the left lower heart chamber before it beats by about 60%, and reduced heart muscle thickening by about 30% ². It also cut interstitial fibrosis, the scar tissue between heart muscle cells, and fat deposits in the heart ². These effects happened without significant weight loss ².

In the minipigs, semaglutide reduced heart thickening, improved an ultrasound measure of filling pressure, and normalized pressure in the blood vessels of the lungs ². Treatment also reversed advanced liver bridging fibrosis, a form of liver scarring ². When treatment began after the disease was already established, it reversed diastolic dysfunction, meaning the heart's relaxation phase improved, and reduced fat deposits inside the heart muscle, around the heart, and in the liver ². Fat under the skin stayed unchanged ².

A retrospective study looked at 7,279 people who started semaglutide through a UK digital weight-loss service between January 2023 and May 2024 ³. The service combined lifestyle therapy with semaglutide ³. Among the 1,678 people who had at least eight medication orders and submitted weight data near the one-year mark, mean weight loss at 12 months was 15.67%, and 92.49% lost at least 5% ³.

Weight tracking frequency showed a clear pattern. People who tracked their weight on fewer than 20 occasions had a median loss of 11.83%, while those who tracked at least 100 times had a median loss of 20.24% ³. That is a difference of 8.41 percentage points ³. The number of medication orders also mattered, with a clear split between people who received fewer than 12 orders and those who received 12 or more ³. People whose records listed Wegovy had a mean loss of 17.68%, while those treated with Ozempic had a mean loss of 14.72% ³.

The kidney findings add detail to the FLOW trial, which already found semaglutide reduced sustained decline in kidney function, end-stage kidney disease, and cardiovascular death in people with type 2 diabetes and chronic kidney disease ⁴. The new trial did not confirm a benefit on its primary MRI outcomes, so the mechanism remains open, but the secondary findings point toward blood flow and fibrosis ¹.

The heart failure animal results sit alongside human evidence. A systematic review found semaglutide improves symptoms, physical limitation, and exercise capacity in people with obesity-related heart failure with preserved ejection fraction ⁵. The new animal work suggests the drug's effect on diastolic pressure and tissue remodeling can occur even when body weight does not change ².

The UK program's average loss of 15.67% among engaged users is close to the 14.9% to 15.2% mean weight loss seen at 68 weeks in the STEP trials of semaglutide 2.4 mg ⁶. The real-world finding adds a practical detail: frequent weight tracking was associated with more loss in this setting ³.

The kidney trial was small, with 106 people, and its primary MRI measures did not change significantly ¹. The secondary findings need confirmation in larger groups before they can be taken as proof of how semaglutide protects the kidney ¹. The animal heart and liver findings come from rats and minipigs, and results may not translate to people ². The real-world UK study could only analyze 1,678 of the 7,279 people who started, so the 15.67% mean loss may not represent everyone who began the program ³. People who track weight more often may simply be more engaged in other parts of care, so frequency of tracking cannot be separated from those other behaviors in this analysis ³.