AI-assisted study of 101,243 patients links brown fat to lower odds of diabetes and heart disease

Every day, people in cancer care lie still in a scanner so doctors can check on them. Those scans were never meant to look for brown fat. Now a brown fat study has drawn on the scans and records of 101,243 patients, with AI help, and links brown fat to better health.

The paper, published online in Nature on 14 October, comes from Rockefeller University and Memorial Sloan Kettering Cancer Center in New York, with funding from the US National Institutes of Health (NIH). It roughly doubles the same lab’s 2021 study. It also points to losartan, a common blood-pressure pill, as something that switched brown fat on in lab cells and mice.

Why a cancer scan can spot brown fat

What is brown fat? The key difference in brown fat vs white fat is the job. White fat, most of our body fat, stores energy. Brown fat burns energy to make heat.

PET-CT scans, common in cancer care, follow a sugar tracer through the body. Active brown fat happens to take it up, so brown fat on PET scan images can show up as a side finding. It is rare: in scans from 2018 to 2024, only 7.9% of patients had brown fat on at least one scan. The authors note there is no reliable simple test for it yet.

The AI measured, the records told the story

A machine-learning tool built at Memorial Sloan Kettering outlined brown fat in six body regions and measured how active it was. It did this for about 8,700 patients, a job too slow to do by hand. The AI did not diagnose anyone; the health links came from medical records.

The team matched 8,897 people with brown fat to 17,405 without, by age, sex, body mass index and outdoor temperature on the scan day. People with brown fat had about 58% lower odds of type 2 diabetes and 47% lower odds of chronic coronary heart disease. For the first time, according to NIH and Rockefeller, brown fat was also linked to lower odds of depression (about 32%) and anxiety (about 22%).

Higher activity went with lower odds of heart and metabolic disease, most of all in the armpit.

Losartan, tested only in cells and mice

In the records, people taking losartan or valsartan, two blood-pressure drugs from one family, were more likely to have brown fat. Some antidepressants were linked to less.

The team then tested losartan directly. In lab-grown mouse brown fat cells, higher doses raised the main heat-making protein. In healthy mice, losartan raised energy use.

In the cells, losartan worked through a different switch from the one that lowers blood pressure. First author Nicolás Gómez-Banoy says future treatments might use that for brown fat activation in people with normal blood pressure. Still, losartan is not a weight-loss drug; the mice did not lose weight. “This is just a start,” said senior author Paul Cohen of Rockefeller, pointing to other medicines in the records.

The open question is cause and effect

The study looks back at records. It shows people with brown fat had these conditions less often, not that brown fat protects anyone. Healthier people may simply keep more of it. The authors call for larger forward-looking studies.

All the patients came from one cancer centre, and about 78% of the matched group were women. The scans were done without cold exposure, so some brown fat may have been missed. A few skin conditions were more common in people with brown fat.

We found no comment from scientists outside the study. Griffin Rodgers, director of the NIH institute that helped fund it, said it gives a clinical reason to study brown fat as a treatment target.

If you take blood-pressure pills, nothing changes today

Please do not start, stop or change any medicine, including losartan or antidepressants, because of this study. If you have questions, talk to your doctor or pharmacist. The study tested no cold plunges, supplements or exercise, so it offers no daily tips.

A clearer map of brown fat, not yet a treatment

The good is real. AI helped turn routine scans into a large brown fat study. The findings repeat the 2021 links at twice the size and add mental health.

The limits are just as real. Links are not causes, the patients came from one centre and were mostly women, and losartan has only been tested in cells and mice. On balance, this is a strong map of brown fat, not yet a reason to change anything. We will keep following it in our science news.

No clinical trial has tested losartan on human brown fat yet. Until one does, the safest place for this finding is the lab, not the medicine cabinet.