If you think that all fat cells are inert, metabolically inactive storage containers that swell up with triglycerides, especially when we overindulge in carbohydrates, think again. The two major types of fat produced by our body are brown and white fat. White fat is relatively inert and fits our traditional impression of fat cells as inactive fat storage depots that make us fat, but brown fat cells are actually calorie-burning metabolic machines.
What's the role of brown fat? Newborns don't have the ability to shiver in cold temperature to keep their little bodies warm, so they have increased stores of heat-producing brown fat to compensate. So white fat stores energy in the form of triglycerides, while precious brown fat burns energy. In addition to burning more calories at rest, brown fat cells which are also known as “BAT” (brown adipose tissue) actually mop up triglycerides and glucose molecules from the blood, using them as fuel. In my book I emphasize the role of triglycerides as a major risk for heart disease, so having more brown fat accelerates the clearance of these dangerous excess triglyceride particles. High blood glucose in someone with diabetes can damage nearly every major organ in your body from your eyes to your heart and kidneys, so having brown fat to soak up and burn extra blood sugar is a major advantage.
The ability of brown fat to gobble up glucose is also what is used to image them using a test called the PET-CT scan. In this test patients are injected with radioactive sugar molecules which travel directly to hungry brown fat cells, lighting them up so they can be visualized on a CT scan. Unfortunately as we grow into adulthood and generate other adaptations to staying warm like shivering, accumulating more body fat for insulation, and inventing central heating to keep our bodies warm, our precious brown fat stores diminish.
How Can I Get Some Brown Fat?
Although it may not be possible right now to increase your brown fat stores, you can do some things to make your inactive white fat start behaving more like your brown fat. Scientists refer to this shift in white fat cell behavior as “browning.” Thermogenin (aka UCP1) is a key protein that allows brown fat to burn energy by generating heat (aka thermogenesis). Right now there are 2 major factors that have been researched that can allow those inert white fat cells to start making thermogenin so they can burn calories like brown fat.
1. Cool Down: Studies show that cooling your body to 63 degrees or lower for two hours a day for six weeks can increase the activity of thermogenin in white fat cells, allowing white fat to burn more calories at rest.
2. Move More: Exercising muscles release a hormone called irisin which allows white fat to start acting brown, again burning more calories. Add this to the already endless list of exercise benefits.
How are these 2 factors connected? When you are exposed to cold weather, if your fat cells can't produce enough heat, your muscles are forced to contract or “shiver.” Shivering muscles produce irisin which allows your fat cells to generate heat to help keep you warm. One study showed that 10-15 minutes of cold-induced shivering led to an equivalent rise in irisin compared to an hour of moderate exercise. I don't recommend replacing exercise with shivering sessions given the myriad benefits of exercise, but it is interesting to note that the effects on fat-induced thermogenesis appear to be similar. Does this also mean that exercising in very cold conditions triggers even greater fat burning? Not necessarily. As a matter of fact, there are lots of metabolic advantages to exercising in heat, also known as hyperthermic conditioning. This has been popularized and nicely summarized by Dr.Rhonda Patrick in this video.
What About South Asians?
Once again, we South Asians have been dealt a metabolically unfair card. You would think that our brown skin may in some way earn us some extra brown fat, but unfortunately a study done comparing South Asians with Caucasians found lower amounts of brown fat in South Asians. In terms of body temperature regulation, this does make sense. South Asians originate from a hot tropical climate where there is no need to generate extra body heat, which may explain why we are relatively deficient in brown fat. Our ancestors worked and played outdoors in sunny, hot climates so they didn't need brown fat stores to provide extra body heat. They also didn't need the metabolic advantages of brown fat since staying physically active in hot climates provided us with the multiple beneficial effects of hyperthermic conditioning mentioned above, such as a boost in growth hormone to maintain lean muscle tissue and a release of heat shock proteins (aka HSPs) which helps protect against insulin resistance, an epidemic in South Asians. Add to that the additional benefits of adequate vitamin D levels from sufficient sun exposure in our ancestors (most South Asians today are significantly deficient in Vitamin D) and you can appreciate how our modern day indoor lifestyles have led to a significant metabolic disadvantage predisposing us to obesity and insulin resistance.