For most people, “fat,” particularly the kind that bulges under the skin, is a four-letter word. It makes our thighs jiggle and lingers despite torturous attempts to eliminate it. Too much increases the risk for heart disease and type 2 diabetes. For decades researchers have looked for ways to stop its storage.
But now we know all fat is not created equal. In the late 2000’s several research groups independently discovered something that shattered the consensus about the absolute dangers of body fat. Scientists had long known that humans produce at least two types of fat tissue- white and brown. Each white fat cell stores energy in the form of a single large, oily droplet but is otherwise relatively inert. In contrast, brown fat cells contain many smaller droplets, as well as chestnut-colored molecular machines known as mitochondria. These organelles in turn burn up the droplets to generate heat.
Babies, who have not yet developed the ability to shiver to maintain their body temperature, rely on thermogenic deposits of brown fat in the neck and around the shoulders to stay warm. Investigators initially assumed that all brown fat disappears during childhood but new findings revealed otherwise. Adults have brown fat, too.
Suddenly, people started throwing around terms like holy grail to describe the promise of brown fat to combat obesity. The idea was appealingly simple: if researchers could figure out how to incite the body to produce extra brown fat or somehow rev up existing brown fat, a larger number of calories would be converted into heat, reducing deposits of white fat in the process.
Recent experiments revealed brown fats benefits go far beyond burning calories. A 2011 study found that brown fat can fuel itself with triglycerides taken directly from the bloodstream. The exact kind of fatty molecules that increase the risk of cardiovascular disease and is known to increase the chances of developing metabolic syndrome. This is a cluster of conditions that raises the risk for not just heart disease but stroke and diabetes as well. Brown fat cells also draw sugar molecules from the blood, which could help lower the risk for type 2 diabetes.
But activating this fat often takes extremely low temperatures.
In one study, participants remained inactive for three hours while wearing a cold suit that circulated water with a temperature of 64.4 degrees Fahrenheit over their skin- cold enough to lower their body temperature without causing too much shivering. That way the researchers could be sure that most of the extra calories burned during those three hours were expended by brown fat cells rather than quivering muscles. The volunteers burned an extra 250 calories compared with what they would have used up during three hours of inactivity at more typical indoor temperatures. Although that may not sound like a lot, an extra 250 calories a day for two weeks would consume enough energy to allow a dieter to lose a pound of fat.
Given these findings, an increasing number of scientists and biotech companies are trying to develop ways to multiply the number of brown fat cells in the body or somehow boost their activity. In addition, they are exploring the possibility of transforming white fat cells into tissue that behaves a lot like brown fat- what they call “beige” or “brite” (brown in white) fat. In one study researchers showed low temperatures increased the activity of a gene named UCP1, which seems to guide the conversion of white fat into beige fat.
Exposing your body to cool and even cold temperatures helped to recruit more brown fat cells. Some studies have suggested that just two hours of exposure each day to temperatures around 66˚F (19˚C) may be enough to turn recruitable fat to brown. Taking a cold shower or ice bath, turning the thermostat down a few degrees in your home or going outside in cold weather are other ways to cool your body and possibly create more brown fat.
Don’t fancy low temperatures? Investigators have identified several molecules that may be able to stimulate such “browning” of white fat without the need for cold. A hormone called irisin, which is released from muscle cells after exercise, coaxes white fat to behave like brown fat. In one of these studies, researchers injected mice with a gene that tripled the levels of the hormone in the blood of mice that were obese and had dangerously high amounts of sugar in their bloodstream. The mice lost weight and regained control of their glucose levels in just 10 days.
Exercise has also been shown to increase UCP1 activity in brown fat, making it more active. Other naturally derived browning stimulators currently under investigation include brain-derived neurotrophic factor—a molecule that usually promotes growth of neurons—and SIRT1, a protein whose purpose remains mysterious but that may help the body manage stress.
Brown fat has generated interest because it appears to be able to use regular body fat as fuel. What a great concept. Take all that excess weight and turn it in to usable power. Clearly there’s a lot more we need to know before it’s hailed as the holy grail. No one is recommending an ice bath or freezing to shed pounds. For now, it reinforces the importance of making exercise an integral part of every weight loss program. But who knows where this will take us in the near future.