Fat Fights Fat? How Brown Fat Battles Obesity


As it turns out, increasing certain types of fat can actually help burn fat. The body stores two types of fat, distinguished visually only by color, but biochemically by a complex ecosystem of metabolic machinery with big implications for overall health. The two types of fat, simply known as white and brown fat, are generally characterized by their effects on the body’s fat stores, largely because they are surprisingly and strikingly different. White fat functions solely as an energy store, huddling excess calories (stored in the bonds of fat molecules) until they are needed to complete basic bodily functions (and the body cannot obtain them; for example, during times of nutritional deficiencies, fasting, or physical activity.) Brown fat, on the other hand, has been shown to enhance the body’s metabolic activity, helping to burn fat instead of hoarding it. In particular, brown fat has shown an enhanced capacity to use fat to generate heat.

Babies, for example, who cannot shiver to generate heat, use increased stores of brown fat to regulate their internal temperature. It had long been thought that brown fat disappears with age and that adults are not privy to the same temperature-regulating mechanism as babies, but recent research suggests otherwise. Brown fat deposits have been found in adults (although in smaller quantities)—and that they, too, are activated by colder temperatures. The next question in the logical sequence of events: can adults use brown fat in a manner similar to babies—in particular, as a means to burn fat and prevent the development of diseases, such as cardiovascular disease and diabetes, that often accompany weight gain?

Brown Fat: a Deeper Look

Brown fat is much less abundant that its white counterpart, and is typically organized into distinct lobules at specific locations in the body, including the back between the shoulder blades, along blood vessels in the neck, and around the kidneys and the nearby adrenal glands. Unlike white fat, these globules are known to have a rich supple of blood vessels and be deeply innervated by the nerves of the sympathetic nervous system – the branch of the nervous system responsible for maintaining metabolic homeostasis and, if necessary, mobilizing the “fight-or-flight” stress response. But the most pressing question still lurks unanswered: how does brown fat, a fatty substance in its own right, help to burn calories and stave off fat?

Brown fat has been shown to contain large numbers of mitochondria, the cells energy manufacturing facility. A mitochondria-dense tissue is particularly well adept at burning unused calories to create heat, a process called thermogenesis (a phenomenon typically achieved via muscular activity or increased metabolic rate.) In fact, brown fat is known by that color due to the high number of molecules called cytochromes, which play an essential role in oxidative phosphorylation, the stage of metabolism responsible for the generation of cellular energy. In brown fat, triacylglycerols–the same fatty molecules that constitute white fat and are responsible for a growing waistline–are used as a fuel to ultimately produce heat. This effect is mediated by the release of noradrenaline, the sympathetic hormone that regulates body temperature. Then the presence of a blood supply and nerves of the sympathetic nervous system are explains:

  • Blood vessels direct the nutrients needed for functional mitochondria as well as the fat molecules needed for metabolism.
  • The nerves release the noradrenaline needed to kick-start brown fat’s enhanced metabolic activity.

What the Science Shows

In a 2012 study, a group of six men remained inactive for three hours while wearing a suit circulating water at 64.4 degrees Fahrenheit, cold enough to lower body temperature but not cause excessive shivering (a thermogenic process that will lead to calorie loss.) In this way, calorie loss could be attributed primarily to brown fat activation, and less to shivering. Researchers concluded that volunteers who wore the cold water suits lost 250 more calories compared with what they would have had they sat inactive at normal temperatures. To put that number into perspective, a deficit of 250 calories/day for two weeks is enough to lose one pound of body fat.

A separate 2011 animal study concluded that because brown fat fuels itself on triglycerides, the risk of developing metabolic syndrome, and associated diseases that include heart disease, stroke and diabetes, is significantly reduced.

Activating Brown Fat to Enhance Metabolism

Given the suspected benefits of brown fat, the next step is to find a strategy to maximize its effects. Research in this area is currently very active, as biotechnology companies and university laboratories try to capitalize on brown fat’s recent rise to biological stardom. Currently, only the following is known of our ability to maximize brown fat activity:

1. Because it is currently not clear if we are able to increase the raw amount of brown fat in the body, research has turned to trying to coax the body primary fat, white fat, into behaving like brown fat. The result: something appropriately named “beige” fat. Results of a recent study asking 12 men with lower than average levels of brown fat to sit in a 63 F room for 2 hours/day for six weeks found that:

  • At first, participants burned an average of 108 extra calories when compared against similar circumstances in normal indoor temperatures.
  • After six weeks, the bodies were able to burn an extra 289 calories when compared to normal temperatures, indicating an increase in brown fat-like matter. PET-CT scans confirmed an increase in “beige” fat.

2. It’s no surprise that sitting in the cold is not the most attractive option for losing a few pounds. Two separate studies confirmed that a hormone called irisin, which is produced in muscle cells following physical activity, is able to coax white fat to behave like brown fat. Animals that overproduced irisin–and who were dangerously obese and had high levels of sugar in their blood–lost significant weight and returned their blood sugar to normal levels in just 10 days.

3. At a genetic level, both cold temperatures and exercise increased activity of a gene called UCP1, which is thought to be responsible for the conversion of white fat into brown fat. Other natural substance though to induce browning, brain-derived neurotrophic factor and SIRT1 (that may help regulate stress) are currently under investigation as potential stimulatory agents.

Future Directions

While beige fat is a promising way to boost metabolism and stave off excess fat, it may not be the most efficient. It is thought that brown fat itself is able to burn at least 5x the stored energy than its beige counterpart. Researchers have identified that the more promising approach to maintaining metabolic health may be to try to keep the brown fat stores as active in adulthood as they are during childhood rather than having to completely re-create it.