Why Brown Fat May Matter More Than You Realize for Metabolic Health

When people talk about body fat, the conversation usually centers on how much there is and where it collects. But the kind of fat matters too. Most body fat is white fat, which stores energy for later use. A smaller portion is brown fat, which burns energy to generate heat.

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About the study

Scientists wanted to better understand the full range of health conditions connected to brown fat, not just heart and metabolic disease, and to see whether its activity and location in the body played a role. Earlier work had associated brown fat with lower rates of heart and metabolic problems, but it only categorized people by whether brown fat appeared on a scan, not by how active it was.

For this analysis, the team examined PET-CT scans taken as part of patients' routine cancer care, since active brown fat shows up on those images. They matched 8,897 people with brown fat to 17,405 people without it, using age, sex, BMI, and outdoor temperature on the scan day as matching factors. The researchers then reviewed diagnoses, lab results, and heart imaging from the year that followed.

An AI system assessed brown fat activity in 8,709 participants across six body regions, including the neck, the area above the collarbone, and the underarms.

Lower rates of diabetes and heart disease in people with brown fat

About 2.1% of people with brown fat had type 2 diabetes, compared with 5.1% of those without it. Chronic heart disease caused by reduced blood flow to the heart was also less common, affecting 2.3% of the brown fat group versus 4.1% of the group without brown fat.

People with brown fat also showed lower blood sugar, lower A1C levels, lower triglycerides, and higher HDL, or "good," cholesterol, even after researchers adjusted for factors such as age, sex, and BMI. Brown fat activity mattered as well: the more active it was, the lower the odds of type 2 diabetes, coronary artery disease, heart failure, and atrial fibrillation, an irregular heart rhythm.

The association extended to mental health. Roughly 16.2% of people with brown fat had an anxiety disorder diagnosis, compared with 19.6% of those without it, while 5.4% had experienced a depressive episode, compared with 8.2%. Sleep disorders were also less frequent, at 8.8% versus 10.8%.

Underarm brown fat had the strongest links to metabolic health

Among the six regions studied, brown fat in the underarms was tied to lower rates of every heart and metabolic condition the researchers looked at, including high blood pressure and disorders affecting blood flow to the brain. People with more active underarm brown fat also tended to have less visceral fat, the deeper abdominal fat stored around internal organs.

The researchers believe the lower rates of anxiety and depression may be related to healthier metabolic profiles and reduced visceral fat, both of which previous studies have connected with better mental health.

Because all participants were cancer center patients and the data were analyzed after the fact, the findings show an association rather than a cause-and-effect relationship. The team accounted for cancer type, stage, and treatment, and noted that larger studies tracking people over time are still needed.

Habits that may help activate brown fat

Earlier research has looked at what turns on brown fat, and a few habits appear promising:

• Cold exposure: Short periods in cooler conditions, such as cold showers or time spent in chilly environments, may help stimulate brown fat.
• Regular exercise: Physical activity has been linked to better brown fat function and may help some white fat take on a more metabolically active form.
• Certain foods and supplements: Some studies suggest that capsaicin, the compound that gives chili peppers their heat, and compounds found in green tea1 may help activate brown fat. This research-backed metabolism supplement contains both ingredients, and reviewers praise it for helping curb cravings and support metabolism.

The takeaway

Brown fat is a small but important part of the body's energy-regulating system. In this large study, having more brown fat and more active brown fat was linked with healthier cardiometabolic markers, including blood sugar, blood lipids, inflammation, and heart health. Future research may help determine whether safely stimulating brown fat could become a useful way to support metabolic health.