Can Activating Brown Fat Help Prevent Diabetes and Heart Disease?
Brown fat now looks like a credible treatment target: a Nature study of more than 100,000 patients found that people with more active brown fat had markedly less diabetes and heart disease. Whether deliberately switching it on prevents those diseases remains unproven in people, and the blood pressure drug the researchers flagged increased brown-fat activity in cells and mice. You don't have to wait for that answer. In a randomized trial, exercise cut visceral fat without measurably increasing brown-fat activity.
Brown fat burns energy to make heat, where ordinary white fat stores it, and in mice turning it up protects against obesity and metabolic disease. Whether that matters for adults has been an open question for years. A study published in Nature on October 14 pushes it forward: among patients who had routine PET-CT scans at a cancer center, those with more active brown fat had progressively less diabetes and heart disease, and the researchers identified losartan, a common blood pressure pill, as something that switched brown fat on in the lab.
From brown fat present or absent to how hard it's working
The same team at Memorial Sloan Kettering had already reported, in 2021, that people whose clinical scans happened to show brown fat had less cardiometabolic disease. That work could only say whether brown fat was visible. The new study added scans through 2024, and the newer patients reproduced the earlier pattern. The merged group of 101,243 patients still includes the original ones, though, so it isn't a fully independent replication. After matching on age, sex, BMI and outdoor temperature, and adjusting for smoking, family history, cancer type, stage and treatment, people with detectable brown fat had less than half the odds of a recorded type 2 diabetes diagnosis, along with lower odds of chronic coronary disease and high blood pressure.
The new part is an AI tool that measured how active the brown fat was in 8,709 of the patients who had it. The more active it was, the lower the prevalence of diabetes, atrial fibrillation, coronary artery disease and heart failure, in steps. The broader picture fit: lower glucose, HbA1c and triglycerides, higher HDL, less visceral fat, and hearts with less wall thickening. Not everything lined up, since total and LDL cholesterol ran higher in the brown-fat group.
These are still snapshots of diagnoses already on record, in people being scanned for cancer, which tells you who has less disease and not what prevents it. Cancer type and treatment were themselves linked to brown fat, and adjustment can't remove every difference between groups. The scan also measures glucose uptake, which isn't the same as heat production. In people with type 2 diabetes, brown fat can take up less glucose even when its fat-burning capacity is preserved, so some of the diabetes link could run backward, with diabetes hiding brown fat on the scan.
People with brown fat also had fewer recorded depression, anxiety and sleep diagnoses. Several SSRIs were linked to less detectable brown fat, and the disease-association models adjusted only for broad medication groups, so this is an exploratory finding and no reason to change an antidepressant. Brown-fat-positive patients also had lower bone density in the lower spine, which runs against earlier reports and may be peculiar to cancer patients, but it means any future brown-fat drug trial should check bones.
Losartan is a lead for human testing
When the researchers screened the medications patients were taking, one class of blood pressure drug, the angiotensin receptor blockers, stood out. Losartan and valsartan both went with more detectable brown fat, so the team tested losartan in cells and mice.
| Evidence setting | What was observed | What it establishes |
|---|---|---|
| Cancer-center patients | Losartan users had about a third higher odds of detectable brown fat | An association; people prescribed losartan may differ in other ways |
| Cultured brown fat cells | A heat-producing gene became more active at 50 and 100 μM, but not 10 μM | A cellular response; human brown-fat benefits remain unproven |
| Mice | Losartan raised energy expenditure; body weight and fat mass didn't change | A whole-body effect in animals, with no demonstrated weight benefit |
In the cell work, losartan and a breakdown product acted on PPARγ, a fat-cell switch separate from the receptor that lowers blood pressure. A 2009 study found that people on long-term losartan do carry that breakdown product in their blood and show increased expression of PPARγ target genes in white blood cells. Whether prescribed doses activate human brown fat remains unestablished.
Losartan is approved for high blood pressure, stroke-risk reduction in certain people with hypertension, and certain diabetic kidney problems. It can cause low blood pressure, kidney injury and high potassium, and it carries a boxed warning because it can harm or kill a developing fetus. For an appropriate prescription, established benefits can outweigh those risks. For brown fat alone, with no demonstrated human benefit, they don't justify treatment. This finding isn't grounds for starting losartan, increasing its dose, or switching from another drug that controls your pressure well.
Cold exposure, the other popular way to recruit brown fat, has a similar gap, since the small human studies cited here didn't test durable disease prevention. Small studies found that days to weeks of mild cold improved insulin sensitivity, including in a handful of men with type 2 diabetes, but in that trial brown fat's glucose uptake barely rose and muscle changes appeared to explain much of the effect. In another, improved insulin sensitivity after cold acclimation was evident during cold testing but not at normal temperatures.
Exercise reduced visceral fat without measurable brown-fat activation
A human trial on this question points somewhere useful. In ACTIBATE, 145 sedentary young adults were randomized to 24 weeks of supervised endurance and resistance training or to no program. Vigorous exercise reduced visceral fat, the deep belly fat that the Nature study found less of in people with active brown fat, without a detectable increase in brown fat volume or glucose uptake. So a metabolic improvement you'd hope brown fat would deliver can come without a measurable increase in its activity. The trial was small, in young adults, and didn't count heart attacks or diabetes cases, but large prospective studies link both more physical activity and lower estimated visceral fat to lower cardiovascular risk.
The markers that separated the two groups in the Nature study, glucose, HbA1c, triglycerides and HDL, are ones you can test yourself and track as you change how you train. They can help you assess metabolic health. A brighter brown fat signal on a scan isn't a proven prevention target, at least not yet.
What it would take to make brown fat a treatment
The study gives losartan a specific rationale for a human trial, and the AI tool lets other centers measure brown fat activity in their own patients. The trial that would change the advice would randomly assign people to clinically usable doses of losartan or a suitable comparator, show that brown fat produces more heat, and show metabolic improvement beyond what the drug does for blood pressure, while assessing safety, tracking bone density and enrolling people who don't have cancer. Longer trials counting new diabetes cases and cardiovascular events would then be needed before anyone could call brown-fat activation prevention.