Considering all it does for us, body fat gets a pretty bad rap. Fat, or adipose tissue, is crucial for storing energy, keeping our internal organs safe, helping regulate body temperature, and assisting in the production of many hormones, according to UC Davis Health.
Not all body fat is the same, however. The most common kind is called white fat, or white adipose tissue, and its main function is to store calories for energy. But there is also a second kind of fat called brown fat, or brown adipose tissue (BAT), that exists in small amounts in all adults, serving the simple purpose of keeping us warm when we get cold. White fat can sometimes turn into brown fat, and during that stage it is sometimes known as beige fat.
In recent years, scientists have discovered that BAT may serve an even greater health purpose in terms of weight loss, diabetes, and even heart health. This guide will tell you everything you need to know about what brown fat is, what it does, and how it affects your health.
What Is Brown Fat?
Health researchers became interested in brown fat because of its apparent role in calorie burning and thermogenesis, or the process by which the body generates heat. Compared to white fat, brown fat has significantly more mitochondria, the part of the cell responsible for producing energy, according to Mayo Clinic. That may be why brown fat is most abundant in babies and hibernating mammals. Adults have much smaller amounts of it, usually located in the neck, around the shoulder blades and kidneys, and along the spinal cord, says Kristen Smith, RDN, spokesperson for the American Academy of Dietetics. Because of brown fat’s ability to burn calories, researchers have been studying its role in fighting obesity.
Brown Fat vs. White Fat: What’s the Difference?
White fat is the type most of us are familiar with — it’s the kind the body stores for energy, but it can lead to obesity when it goes unused. “Most of the fat in an adult body is white fat,” explains Smith. Brown fat is found primarily in babies and hibernating mammals, to help with temperature regulation.
The two fats differ not only in function and color but also structure. White fat cells have large droplets of lipids to store energy, while brown fat has smaller droplets and tons of mitochondria, according to Johns Hopkins Medicine. Often referred to as the “powerhouses” of the cell, mitochondria produce energy, and they are signaled by cold exposure to burn calories and kick-start thermogenesis, says registered dietitian Jennifer Maeng, founder of Chelsea Nutrition in New York City. Mitochondria are also iron-rich, which gives brown fat its color, according to a report from the University of Michigan.
What Potential Health Benefits Does Brown Fat Have?
Research on brown fat is relatively new, and much of it is preliminary or has involved animals or only small groups of humans (fewer than 50), so it requires further study. Here is what we currently know about brown fat and the following conditions:
Weight Loss and Metabolism
It is believed that when brown fat is activated (in other words, when its mitochondria are signaled to burn calories and produce heat), it may absorb and use compounds called branched chain amino acids (BCAAs). Past research involving rodents and people links high levels of BCAAs with obesity, insulin resistance, and type 2 diabetes, which suggests that lower levels of it could improve those conditions. Although more research is needed to determine the relationship between brown fat activation via cold exposure and BCAA levels in humans, one small study published in Nature in 2019 examined its effects on the BCAA levels of 33 healthy young men, and found that two hours of cold exposure resulted in lowered BCAA levels in those who already had high brown fat activity. Another study published the same year in Autophagy found that thyroid hormones thyroxine (T4) and triiodothyronine (T3) activated brown fat and thermogenesis in mice, no cold exposure needed. “This is a promising future avenue of research, to link the treatment of obesity and metabolic diseases with the direct effect T3 has on activating brown fat,” says Maeng. “When brown fat is activated, more calories are burned for energy, resulting in better insulin sensitivity and appetite regulation.”
Unlike white fat, brown fat is metabolically active tissue: It burns glucose for fuel. And there is early evidence that brown fat may significantly influence metabolic health. A small study published in April 2022 in The Journal of Nuclear Medicine recruited 34 students and activated their brown fat by lowering their core body temperature. A correlation was found between brown fat and metabolic disorders such as diabetes. The researchers believe that a high level of brown fat activation may be an early warning sign that an individual might develop diabetes, although more rigorous research is needed.
A study published in Nature Medicine in 2021 found a correlation between the presence of brown fat in a person’s body and their risk of cardiometabolic disease. More specifically, it found that those with more detectable brown fat (by way of PET scans) had a lower risk of abnormal cholesterol, coronary artery disease, hypertension, and congestive heart failure.
How to Activate Brown Fat
Human beings tend to have the most brown fat as infants, and we lose much of it as we age. But if brown fat has health benefits, is there a way to increase the amount of it we have?
“It is generally understood that an adult cannot actively increase the quantity of brown fat they intrinsically have,” says Maeng. But while brown fat cannot be created, there is some evidence that the brown fat we have can be activated, and that white fat may potentially be oxidized. Again, the research is still in its early stages, but it does appear that certain conditions may activate brown fat by signaling its mitochondria to burn calories and produce heat. Here is what is currently known about how the following factors contribute to brown fat activation:
A review of studies published in Frontiers in Physiology in 2019 examined the effects of certain foods on thermogenesis, the warming process that activates brown fat. The review largely included studies done on rats, but it found that turmeric and curcumin spices, foods with resveratrol (like wine), green tea, and spicy foods with capsaicin may activate thermogenesis and/or trigger fat oxidation, which is the browning of white fat. Further research is warranted to verify the effectiveness of those ingredients on BAT in humans, especially because the dosages required for some (i.e., resveratrol) to see results may be unrealistically high.
Additionally, a review published in Frontiers in Neuroscience in 2021 found that caffeine evokes BAT thermogenesis in rodents, but its effect on human BAT thermogenesis remains unclear. As a registered dietician, Smith doesn’t feel comfortable recommending dietary changes as a surefire way to activate brown fat. “It would be phenomenal if we could,” she says. “But more research is needed before we can offer advice.”
Various past research done in rodents has found particular herbal supplements, including kudzu flower oil, ginseng, quercetin (a plant flavonoid found in many fruits and vegetables), propolis, and oleuropein (a compound found in green olives) to either activate thermogenesis or oxidize white fat in rodents. The results do not directly translate to humans, however, and more research is required. Also, supplements containing these herbs aren’t regulated by the U.S. Food and Drug Administration. So, if you’re interested in giving one a shot, consult your doctor first.
Increasing your workouts won’t create more brown fat out of the blue, but it might oxidize existing white fat into what researchers call beige fat. “There is a correlation between the level of physical activity you do and a better overall distribution of body fat, including the amount of brown fat,” says Maeng. “Managing your overall body fat by working toward healthy weight goals will improve your overall fat distribution. There have been recent studies that demonstrate how exercising switches the body from storing white fat to beige fat, though it is not clear if the beige fat is directly metabolically beneficial or if it is an adaptive response,” she says.
Taking a polar plunge in an ice bath or cryotherapy chamber can activate your brown fat by triggering thermogenesis, according to a study published in the Journal of Obesity in 2018. But Maeng says that taking a brisk walk in the winter may work just as well. “Adjusting your body to cold temperatures by going for a walk outside or taking an occasional cold shower could help,” she adds.
In a small study published in The Journal of Clinical Investigation in 2020, a drug called mirabegron, typically prescribed for bladder control, was given to 14 healthy women to see if it would activate brown fat. Researchers believed it was a possibility because the drug binds to a protein on the surface of cells that’s thought to also stimulate BAT. After four weeks of treatment, the women’s metabolism at rest was almost 6 percent higher, although their weight or overall body composition — the ratio of fat to muscle — hadn’t changed. Brown fat activity, measured by PET scans, also increased during the study. The largest changes were found in women who had less brown fat activity to begin with. Given the extremely small size of the study, those results are not conclusive at all, and another study found the same drug to be ineffective.
Additionally, the study published in Autophagy in 2019 found that the synthetic thyroid hormones thyroxine and triiodothyronine activated brown fat and thermogenesis in mice. Again, human trials are needed to determine any benefit.
While the ability to harness the power of brown fat in humans for weight loss and other health benefits is promising, scientists don’t have it fully figured out yet. The majority of studies that exist on the topic were done on animals, and further research is needed to nail down how to efficiently activate brown fat in people.