I'll Have More of That Fat, Please! Brown vs. White
Body fat gets a bum rap, and in most cases, deservedly so. Too much of the stuff, and you're prone to a plethora of problems: heart disease, stroke, cancer and diabetes, just to name a few. But what scientists are discovering is that not all fat is bad. In fact, emerging research shows that brown fat may actually do the body good.
White fat is what we know and loathe: It settles in our thighs and rests in our belly. Its primary function, though, is to serve as a storehouse for energy. It's an evolutionary response, explains Sheila Collins, a professor in the metabolic disease program at the Sanford-Burnham Medical Research Institute, to when "food sources were scarce and not very calorically dense."
Think of it like this: "White fat cells are like the bank where you put your money when you have it in times of plenty and then are able to access it later when times are lean," Collins says.
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White fat also cushions our inner organs and insulates our bodies -- all vital things for our general well-being. That is, of course, until we have more fat than we need -- by eating too many calories and burning too few. Then we're in trouble.
According to the Centers for Disease Control and Prevention, more than two-thirds of American adults are overweight, meaning a majority of the population is considered high risk for complications such as sleep apnea, high blood pressure, osteoarthritis and kidney disease. The white fat found in the abdomen, also known as visceral fat, is especially harmful. Metabolically active, it releases inflammatory substances that can damage organs and make the body vulnerable to diseases such as Alzheimer's and cancer.
Now imagine a fat that, instead of storing calories -- a precursor to so many problems -- actually burns them. That's why brown fat (darker in nature due to its many mitochondria) is getting a lot of much-needed attention.
Brown fat is found in babies on their upper spine and shoulders. "When we are born, and for the first few months or years of life, humans have significant amounts of brown fat," says Labros Sidossis, a professor of internal medicine at the University of Texas Medical Branch at Galveston. Babies are unable to shiver to stay warm, so when the temperature drops, brown fat jumps into action through a process called nonshivering thermogenesis, using "significant amounts of blood sugar and lipids to produce heat," Sidossis explains.
This lipid-burning fat was long thought to disappear during childhood, but scientists have discovered that this is not so. Adults apparently have it too, and those with more brown fat happen to be thinner than those with less.
[Read: Are You Suffering From Fat Phobia?]
As we age, most brown fat is lost and replaced by white fat. But it's still there, albeit in small deposits, around the neck, shoulders and spinal cord. Researchers can measure it through a positron emission tomography scan, an imaging test where radiolabeled glucose is injected into a patient. Brown fat, which takes up large amounts of glucose to use as metabolic fuel, then becomes visible. But other methods for measuring, including MRI and thermography, are currently being tested.
In addition to being expensive and using radioactive tracers, PET scans only measure the cells that are actively taking up the labeled glucose, Collins notes. "What is needed is some way to measure total brown fat without regard to whether it is active or not [in order] to determine the total amount present that is potentially capable of being activated and burning energy," she says.
Studies confirm that brown fat in adults can be stimulated by the cold. A 2012 study published in the Journal of Clinical Investigation showed that in men who were wearing suits circulating cold water -- thus reducing their skin temperature by about 3.8 degrees Celsius -- their brown fat burned energy to create body heat. Metabolic rates increased by 80 percent, and some 250 calories were burned over three hours.
Better yet, more recent studies are showing that colder temperatures can create brown fat. "Reducing the average temperature in a room can induce brown fat when done chronically," says Philipp E. Scherer, director of the Touchstone Diabetes Center at the University of Texas Southwestern Medical Center. His 2013 study published in Nature Medicine discovered newly generated brown fat cells in mice exposed to cold.
And in a study published in June in Diabetes, subjects who slept in a room set at 66 degrees Fahrenheit for four weeks increased their brown fat by as much as 40 percent. When temperatures were raised in the subsequent weeks -- to a high of 81 degrees -- their levels of brown fat decreased.
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"Precursor cells present in white fat can be prompted to become energy-burning brown fat," says Yu-Hua Tseng, an associate professor of medicine at Harvard Medical School. In fact, her lab discovered that bone morphogenetic protein 7 , a growth factor, could trigger the process in such cells isolated from surgically discarded tissue or liposuction.
"Much more exciting," Sidossis says, "is the prospect that, under certain conditions such as prolonged severe stress, the abundant white fat of our body may turn into brown-like fat, transforming from an energy-storing [tissue] to an energy-consuming [one]."
Beyond burning fat, which is all well and good, brown fat is further proving its worth with its role in the fight against diabetes. In a study published in July in Diabetes, Sidossis and his colleagues demonstrated that in men with 1 to 3 ounces of brown fat, exposure to mild cold -- sitting in a room at 65 to 70 degrees Fahrenheit -- not only increased energy expenditure by about 15 percent, or approximately 300 calories over 24 hours, it also increased blood sugar removal (as much as 25 grams) from the blood. This is a significant finding, Sidossis explains, given that people with Type 2 diabetes have only 2 to 3 grams more sugar in their blood. "Men with brown fat have improved insulin sensitivity, regulating blood sugar easier and better than those who don't have brown fat."
Can it be as easy as turning down the thermostat to improve one's health? Scherer acknowledges that with a lot of brown fat, an adult could lose as many as 300 to 400 calories a day, "so we should think of it as a possible anti-obesity approach." But, he adds, "We have to bear in mind that these are relatively modest changes in calorie waste. However, the metabolic improvements associated with increased brown fat may have a significant potential for anti-cardiovascular disease and anti-diabetic treatment regimens."
Collins says, "With a crisis in obesity and the risks it creates for diabetes and heart disease ... being able to harness the power of brown fat holds great promise in the arsenal of weapons against metabolic disease: exercise, diets of lower caloric content and increased nonshivering thermogenesis."
