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You Probably Didn't Think Fat Could Help Your Metabolic Health
When we talk about body fat, we tend to focus on how much we have and where it's stored. But the type of body fat also matters. Most of your body fat is white fat, which stores energy for later. A much smaller share is brown fat, which uses energy to produce heat.
Adults do carry some brown fat, but measuring how active it is across large groups of people has been difficult. To get around that, researchers turned to artificial intelligence and a large data set of medical scans to see how brown fat lines up with health across the entire body.
About the study
The researchers set out to identify the full range of health conditions tied to brown fat, beyond heart and metabolic health, and to find out whether how active it is, and where it sits in the body, makes a difference. Their earlier work had linked brown fat to lower rates of heart and metabolic disease, but it only sorted people by whether brown fat showed up on a scan, not by how much of it was working.
For this analysis, the team reviewed PET-CT scans done as part of patients' regular cancer care, and brown fat appears on them when it's active. The team matched 8,897 people with brown fat to 17,405 people without it, pairing them by age, sex, BMI, and outdoor temperature on the day of the scan. They then compared diagnoses, lab work, and heart imaging from the following year.
An AI tool measured brown fat activity in 8,709 of those participants across six areas of the body, including the neck, the area above the collarbone, and the underarms.
Fewer cases of diabetes & 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. Rates of chronic heart disease caused by reduced blood flow to the heart were 2.3% in the brown fat group and 4.1% in the group without it.
People with brown fat also had lower blood sugar, lower A1C (a measure of average blood sugar over a few months), lower triglycerides, and higher HDL ("good") cholesterol, even after accounting for factors like age, sex, and BMI. How active the brown fat was also mattered. The more active someone's brown fat, the lower their odds of type 2 diabetes, coronary artery disease, heart failure, and an irregular heart rhythm called atrial fibrillation.
The pattern extended to mental health. About 16.2% of people with brown fat had an anxiety disorder diagnosis, compared with 19.6% of those without it, and 5.4% had a depressive episode, compared with 8.2%. Sleep disorders were also less common (8.8% versus 10.8%).
Underarm brown fat showed the strongest ties to metabolic health
Of the six areas measured, brown fat in the underarms was linked to lower rates of every heart and metabolic condition the researchers examined, including high blood pressure and conditions affecting blood flow to the brain. People with more active underarm brown fat also carried less visceral fat, the deeper fat stored around the organs in the belly.
The researchers suggest the lower rates of anxiety and depression could relate to healthier metabolic profiles and less visceral fat, both of which past research has tied to better mental health.
As every participant was a patient at a cancer center and the data were reviewed after the fact, these findings show a connection rather than cause and effect. The team accounted for cancer type, stage, and treatment, and notes that larger studies following people over time are still needed.
Habits that may activate brown fat
Earlier research has explored what switches brown fat on, and a few habits show promise:
- Cold exposure: Brief exposure to cold temperatures, like cold showers or spending time in cooler environments, may help activate brown fat.
- Regular exercise: Physical activity has been linked to improved brown fat function and may help convert some white fat into a more metabolically active form.
- Certain foods and supplements: Some research suggests capsaicin, the compound that gives chili peppers their heat, and compounds in green tea1 may help activate brown fat. This research-backed metabolism supplement provides both of these ingredients, and reviewers love it for curbing cravings and improving their metabolism.
The takeaway
Brown fat is a small (but important) part of the body's energy-regulating system. In this large study, its presence and activity were associated with more favorable cardiometabolic markers, including blood sugar, blood lipids, inflammation, and heart health. Future studies can help determine how safely activating brown fat could become a useful strategy for improving metabolic health.
