Learn the main colors of adipose tissue and the health implications associated with each type.
Just like muscle, body fat plays an essential role in supporting your health. Also known as adipose tissue, fat stores energy, sends signals to the brain, liver, and muscles to control physiological processes (such as appetite regulation), and promotes metabolic health, says Shingo Kajimura, Ph.D., a Harvard Medical School professor and an investigator in the Division of Endocrinology, Diabetes & Metabolism at the Beth Israel Deaconess Medical Center.
That said, too much body fat can be detrimental to your health, and certain “colors” of fat — determined by the number of mitochondria in each fat cell — may be particularly harmful, says Kajimura. Here’s what to know about the three main colors of fat and how they impact your well-being.
White Fat
Boasting a small number of mitochondria, white fat makes up roughly 90 percent of the fat in a person’s body. However, the exact amount may be influenced by genetics, lifestyle, and environmental factors, which scientists in the field are currently investigating, says Kajimura. This type of body fat is primarily utilized as storage for extra energy, he notes.
In addition to being subcutaneous (located under the skin), white fat can be visceral, meaning it lies within the abdominal walls and surrounds your internal organs, he notes. “We know from multiple studies that visceral adiposity… is associated with a metabolic disease,” he adds. Specifically, visceral fat constantly releases free fatty acids into your circulation and may contribute to high insulin levels, high cholesterol or fat levels in the blood, and the thickening or hardening of the arteries, all of which are features of metabolic syndrome, research suggests. One potential mechanism: inflammation, which is often greater in individuals with higher levels of visceral fat and is linked with insulin resistance and other diseases, says Kajimura.
Brown Fat
Unlike energy-storing white fat, mitochondria-rich brown fat is energetically active, playing a role in maintaining body temperature and creating heat through a process known as non-shivering thermogenesis, says Kajimura. Say you step outside during a cold winter day. To counteract the chilly temps and keep your body warm, your muscles will shiver. However, your body can’t shiver for prolonged periods, as lactate (a metabolic byproduct) will build up, he explains.
That’s where brown adipose tissue can come into play, as it produces heat and regulates body temperature by breaking down blood sugar and fat molecules in colder environments, according to an article published by Proceedings of the National Academy of Science (PNAS). This type of fat is primarily located near the neck, kidneys, collarbone, and spinal cord, per PNAS.
This heat-generating process can have beneficial impacts. In a 2019 study led by Kajimura, 33 young men with varying brown fat activity levels were exposed to chilly temperatures (66°F) for two hours to further activate the adipose tissue. After the cold exposure, the participants with higher levels of brown fat activity had lower amounts of branched-chain amino acids (BCAAs, high levels of which are linked with obesity and type 2 diabetes) in their bloodstreams. Essentially, the highly active brown fat broke down more BCAAs before they could circulate through the body, per PNAS.
“A lot of studies have found that this energetically active brown fat is protective against metabolic disease,” says Kajimura. For example, a 2021 study of more than 50,000 individuals found that people who have brown fat are less likely to suffer from type 2 diabetes, dyslipidemia, coronary artery disease, cerebrovascular disease, congestive heart failure, and hypertension.
While brown and beige fat (more on that later) generally make up about 10 percent of your body fat, the exact amount varies from person to person, says Kajimura. “Some people have a lot, some people don't have enough, and what makes the difference is an exciting area of research now,” he adds.
An important caveat: Many of the current studies investigating brown fat’s effects have been conducted on rodents, so the potential benefits may not fully apply to humans. Assessing brown fat activity is also difficult; to determine activity, many studies utilize PET/CT images showing the amount of glucose uptake in brown fat tissue, an indirect measurement that also exposes people to radiation, according to PNAS.
Harnessing brown fat’s therapeutic effects without causing harm, particularly among at-risk populations, in real life is challenging. While cold environments can activate brown fat, they also increase blood pressure via vasoconstriction to prevent heat loss — a reaction that can be harmful in people with cardiovascular disease, says Kujimara. “That's one of the major hurdles in terms of translatability, to uncouple those beneficial effects of brown fat [and the] detrimental effects on blood pressure.”
Beige Fat
Experts are looking into methods to convert white fat into brown fat, such as using CRISPR gene editing, per PNAS. However, some cells, known as beige fat cells, can transition between adipose tissue colors in certain environments.
Stored within white fat tissue located just below the skin, beige fat cells are technically a highly recruitable form of brown fat that’s activated by cold exposure, says Kajimura. If you were to expose yourself to cold temps (think: 66°F) for two hours daily for 10 days to three weeks, these cells will increase in mitochondria and “brown,” so to speak, he explains. “A lot of studies say lifestyle matters,” he notes. “Cold exposure is so far the most potent stimuli [for] browning of white fat,” such as swimming in cold water.
Triggering the formation of beige cells within white adipose tissue may minimize the negative impacts of excess white fat and improve overall metabolic health, according to research published in Frontiers in Endocrinology. That said, beige fat cells will gradually decrease in mitochondria and increase in white characteristics when the browning stimulus is removed, such as by returning to a warm environment, per the Frontiers research.
The Bottom Line
Recent research findings suggest brown fat can support health and reduce the risk of conditions such as type 2 diabetes and coronary artery disease, while excess white fat (particularly the visceral type) may increase the risk of metabolic disease. Still, research investigating the factors that affect how much brown fat a person has — and how to convert white adipose tissue into its brown counterpart — is limited, and more information is needed to establish firm recommendations.