By Lisa Maguire
Humans have two types of fat – white and brown. Before 2009, it was believed that brown fat only existed in infants. It acts as an internal thermal blanket, and because babies don’t have the ability to shiver, it’s incredibly important. After researchers discovered that the presence of brown fat continues through adulthood, subsequent studies were able to identify other important roles it plays.
Our knowledge about brown fat is relatively limited, especially with regard to how it works in human adults. It’s difficult to locate in the body, so it’s hard to study. Human adults don’t have much brown fat that researchers can find – on average there’s only teaspoons, and it originally had to be located with PET/CT scans and with the use
of radioactive glucose. Scientists have since found ways to uncover it using MRIs, but brown fat is typically mixed in with regular white fat, and while it can often be found in the neck and shoulders of the body, not all humans carry it there.
White fat is the fat we’re all very familiar with – the persistent fat that can be hard to rid. White fat includes subcutaneous fat and visceral fat. It stores energy inefficiently; most fat cells contain a single oily droplet. Brown fat stores multiple smaller droplets and houses mitochondria that burn those droplets to create heat.
In addition to assisting the body in regulating temperature, brown fat has also been shown to burn calories during sleep and increase metabolic activity during the day. In a study published in Diabetes, participants who slept in temperature-controlled environments at 66° Fahrenheit for four weeks nearly doubled their brown fat stores and increased insulin sensitivity – important news for those who have type two diabetes or are pre-diabetic. They also burned more calories during the day.
Interestingly, once the participants were asked to sleep in a warmed room – 81°
– the results were not only reversed, but their brown fat stores actually decreased. Another study showed that two hours spent in a room set at 59° wearing only summer clothing caused brown fat to burn another 100-250 calories depending on the person. Researchers have also shown that exercising in cool temperatures can help stimulate brown fat. Even more interesting – white fat can be coaxed to perform like brown fat.
Another study showed that while people with low levels of brown fat burned more calories in the cold when first exposed to it (64.4° Fahrenheit, to be exact), those expenditures were lower than people with higher levels of brown fat. Repeated exposure to the cold increased the amount of white fat that behaved like brown fat, otherwise referred to as “beige” fat, and after six weeks, instead of burning just 108 calories in a two-hour exposure, they were burning 289.
In addition to cold stimuli, what can increase the behavior of white fat to perform like brown fat? Exercise! Exercise causes a hormone called irisin to be released, which is great at getting white fat to start burning its oily energy store. Several studies on mice have been conducted with regard to brown fat, as it is prevalent in small mammals, and one study showed that a tripled amount of irisin caused obese mice with blood levels of glucose severely heightened to lose weight and regain control of their sugar levels in less than two weeks.
Researchers are eager to capitalize on these findings, looking for the weight-loss “silver bullet.” While further investigations continue, you could ramp up your exercise regimen or, even easier, begin sleeping in the cold.
