Is "Good Fat" Real? Diabetes Rates Are More Than Halved in Those With Brown Fat

On the Trail of Fat That Burns Energy: AI Scanned 100,000 PET-CTs, and a Blood Pressure Drug Stood Out

Not all body fat is the same. White fat stores energy, while brown fat burns energy to produce heat. In a study published in Nature on October 14, 2026, researchers used artificial intelligence to analyze data from 101,243 patients who underwent PET-CT scans at Memorial Sloan Kettering Cancer Center in the United States. People with brown fat had lower rates of type 2 diabetes, heart disease, depression and anxiety disorders, and losartan, a widely used blood pressure drug, activated brown fat in cell and mouse experiments. We have previously covered the health effects of abdominal (visceral) fat; this study helps us understand the "good" side of fat.

Why does this matter?

Obesity is one of the most important risk factors for type 2 diabetes, hypertension, cardiovascular disease and many types of cancer. Most adipose tissue is white fat, which stores energy as triglycerides. Brown fat, by contrast, converts energy into heat thanks to its abundant mitochondria and a protein called UCP1. Long known in infants, this tissue came to be seen as a new target against obesity and metabolic disease after studies from 2009 onward showed that it is also present in adults and can be stimulated by cold.

Studying the link between brown fat and health at a large scale in humans, however, has been difficult. The most common way to see this tissue is on PET-CT scans performed in people with cancer. In oncology practice, brown fat around the neck and collarbone takes up glucose and therefore sometimes appears as a false-positive finding that mimics cancer. This study turns a finding known in oncology as a "source of confusion" into a vast source of data.

What is brown fat, and what does it do?

Brown fat is a specialized type of adipose tissue that burns energy to produce heat instead of storing it. In adults it is found mainly in the neck, above the collarbone, in the armpit, in the chest cavity and along the spine. It is activated by cold and uses up blood glucose and fats. People with active brown fat have lower rates of metabolic and cardiovascular disease.

Brown fat is detected more often in women, younger people, lean individuals and during cold seasons. In this study as well, the frequency of brown fat declined with increasing age, ambient temperature and body mass index. The researchers therefore compared 8,897 patients with brown fat against 17,405 patients matched for age, sex, body mass index and outdoor temperature on the day of the scan.

What did the study find?

1. A screen of all diagnoses: cardiovascular and mental health stood out

Without a prior hypothesis, the researchers compared 511 diagnosis codes recorded in the year after the scan with the presence of brown fat. In multivariable analyses, 98 diagnoses were significant; 92 of them were less common in people with brown fat. By organ system, the strongest association was with cardiovascular disease, followed by mental and behavioral diagnoses. This second finding had not been described before, and it is of particular interest given how common depression and anxiety are among people with cancer.

Of the six diagnoses that were more common in people with brown fat, five were skin conditions. Osteoporosis also tended to be more common in this group, and bone density scans showed lower T-scores in the lumbar spine. The authors stress that future studies of brown fat-targeted therapies should also monitor bone health.

2. Region-by-region measurement with AI: the armpit stood out

Using a machine learning tool that processes PET and CT images together (3DF, based on nnU-Net), the team semi-automatically measured the volume and glucose uptake of brown fat in six regions in 97.9% of patients with brown fat (8,709 patients). This would be nearly impossible to do by hand across thousands of scans. Much like models that detect multiple diseases from a single blood sample, AI here extracts new knowledge from big data. It is a good example of AI in medical imaging.

• Dose-response relationship: As total brown fat activity increased, type 2 diabetes, atrial fibrillation, coronary artery disease and heart failure became progressively less common.
• Regions behave differently: The area above the collarbone (supraclavicular) was the most common site. However, the strongest and most consistent protective association was with armpit (axillary) brown fat; higher activity there was linked to less of every cardiovascular and metabolic condition, including hypertension. Unexpectedly, high activity in the neck region was associated with more hypertension.
• White fat distribution: As brown fat activity increased, visceral (abdominal) fat decreased and subcutaneous fat increased. This "healthier" fat distribution was again most pronounced in the armpit region.

3. Blood tests and echocardiography

People with brown fat had lower fasting blood glucose (the link between diabetes and cancer is also worth remembering), HbA1c, triglycerides and remnant cholesterol, and higher HDL cholesterol. Paradoxically, total and LDL cholesterol were slightly higher. Liver enzymes, the FIB-4 score (an indicator of liver fibrosis risk) and markers of inflammation (neutrophil count, neutrophil-to-lymphocyte ratio, erythrocyte sedimentation rate) were lower. Given the link between fatty liver disease and cancer, this finding is of interest. On echocardiography, left ventricular mass and wall thickness were lower, as was pulmonary artery pressure; in other words, there were fewer signs of adverse cardiac remodeling.

4. Medications: 39 drugs linked to brown fat

Of 125 medications taken in the month before the scan, 39 were significantly associated with the presence of brown fat. This "drug screen" also correctly picked up medications already known to suppress brown fat, an important sign that the method is reliable.

An OR above 1 means brown fat was more common among people taking the drug; below 1 means it was less common. This table does not show cause and effect; for example, people taking beta blockers may already have heart disease.

5. Losartan in the lab: how does it activate brown fat cells?

The researchers tested this clue from human data in the laboratory. In brown fat cells, losartan increased UCP1, the protein responsible for heat production, as well as oxygen consumption; the effect was even stronger in combination with norepinephrine. Surprisingly, the effect did not run through the angiotensin receptor by which losartan lowers blood pressure, but through PPARγ, a key regulator of metabolism. A breakdown product (EXP3179) that has no effect on blood pressure even showed the same effect.

In mice, two weeks of losartan increased thermogenic genes in brown fat and boosted heat production in response to stimulation. Mice given losartan had higher energy expenditure both at room temperature and in the cold, but their body weight, fat mass and muscle mass did not change. A tendency toward higher food intake in the cold may explain this.

How should the results be interpreted?

Strengths

• The largest human brown fat study to date: more than 100,000 patients and a hypothesis-free screen covering all diagnoses.
• The first measurement of regional brown fat activity in thousands of patients, demonstrating a dose-response relationship.
• Known drug effects (beta blockers, antidepressants, corticosteroids) were correctly detected.
• The clue from human data was supported at the mechanistic level by cell and mouse experiments.

Points to keep in mind

• Association, not causation: The study is retrospective and cross-sectional. It is possible that brown fat protects against disease, but also that brown fat is simply easier to detect in healthier people. For example, people with heart disease often take beta blockers, and these drugs suppress brown fat.
• Measurement method: PET-CT measures glucose uptake by brown fat, not its heat production. In people with insulin resistance, glucose uptake may be reduced and brown fat may "go unseen." Using analyses of metformin and olanzapine, the authors argue that this effect alone does not explain the findings, but it cannot be ruled out entirely.
• A cancer patient population: The patients came from a cancer center, 78% were women, and breast cancer was common. Although the analyses adjusted for cancer type and treatment, the results may not apply directly to the general population.
• Scans were not performed in the cold: Brown fat is best seen after cold exposure; its frequency on routine scans (7.9%) may be an underestimate.
• Losartan data are not from humans: The effective concentrations in cell experiments (50–100 micromolar) are well above the blood levels reached in humans at standard therapeutic doses. In mice, energy expenditure increased but body weight did not change. Whether losartan affects brown fat or body weight in humans has not been tested.

What do these findings mean in everyday life?

• Do not take losartan to lose weight or increase brown fat: Losartan is a prescription blood pressure medication; in someone with normal blood pressure it can cause dizziness, low blood pressure, high potassium levels and impaired kidney function. It should not be used during pregnancy. Its efficacy and safety for this purpose have not been tested in humans.
• Do not change your blood pressure medication on your own: Angiotensin receptor blockers are already among the first-choice blood pressure drugs for many patients. If you take a beta blocker or an antidepressant, do not stop it based on this study; these drugs have proven benefits for heart and mental health.
• What is proven has not changed: It has not yet been shown that increasing brown fat lowers disease risk. The well-supported paths to heart and metabolic health remain the same: a healthy weight, a smaller waistline, regular exercise, a Mediterranean-style diet, not smoking and enough sleep. A large study showing that people without risk factors live more than 10 years longer supports this as well. Studies showing that diabetes can be put into remission with lifestyle changes are a good example.
• Be moderate about cold exposure: Small studies have shown that regular exposure to mild cool temperatures increases brown fat, but it has not been proven to prevent disease. Patients receiving chemotherapy, especially those taking drugs that cause cold sensitivity, should take extra precautions in cold weather.
• If your PET-CT report mentions "brown fat": This is usually a harmless, even favorable finding; it does not mean the cancer has spread. Still, be sure to discuss its interpretation with your doctor.

Frequently asked questions

What is brown fat?

Brown fat is a specialized type of adipose tissue that burns energy to produce heat instead of storing it. In adults it is found in the neck, above the collarbone, in the armpit, in the chest and along the spine; it is activated by cold and uses up blood glucose and fats.

Are people with brown fat healthier?

In this study of 101,243 patients, people with brown fat had lower rates of type 2 diabetes, heart disease, hypertension, depression and anxiety disorders. However, the study shows an association; it has not been proven that brown fat directly prevents these diseases.

Does losartan cause weight loss?

No, this has not been shown. In cell and mouse experiments, losartan activated brown fat and increased energy expenditure in mice, but the mice did not lose weight. It has not been tested for this purpose in humans; losartan should only be used on a doctor's advice for approved purposes such as lowering blood pressure and protecting the kidneys.

How can brown fat be increased?

Small studies have shown that regular exposure to mild cold and certain drugs can activate brown fat. However, this has not been proven to lower disease risk. A healthy weight, regular exercise and a balanced diet are the paths with strong evidence.

Glossary

Brown adipose tissue

Mitochondria-rich adipose tissue that converts energy into heat thanks to the protein UCP1.

White adipose tissue

Adipose tissue under the skin and in the abdomen that stores energy as triglycerides.

UCP1

The protein in brown fat cells that enables energy to be converted into heat.

PPARγ

A nuclear receptor that regulates the development and metabolism of fat cells; also the target of some diabetes drugs.

Angiotensin receptor blocker (ARB)

A class of drugs, such as losartan and valsartan, that lowers blood pressure by blocking the action of the hormone angiotensin II.

Propensity score matching

A statistical method that reduces confounding by making the compared groups similar in characteristics such as age and sex.