Brown fat acts as an “internal heater” to warm the blood as it flows back to the heart and brain from the body’s cold extremities. It serves as the first line of defense against the cold. According to research, in children, about 2 to 5% of body weight is composed of brown fat.
When feeling cold, your body starts to burn fat… but not the type of fat we usually think about. There are two types of fat: white fat and brown fat.
Infants are born with a lot of brown fat.
White fat is what we commonly refer to as “fat.” It is called white fat because it appears white. White fat exists throughout the body to cushion our bones and organs. White fat cells serve many functions, with one of the most important being that they are the primary energy source for the body.
In contrast, brown fat consists of much smaller cells, making it look more like muscle than fat. Instead of a large lipid droplet in white fat cells, brown fat cells are tightly packed with mitochondria. This is why they appear brown.
Brown fat, rather than serving as an energy reserve for organs in the body, uses its power to actively burn energy. Unlike white fat, brown fat is found in specific areas such as the neck, shoulders, upper arms, spine, and some parts of the abdomen.
Brown fat surrounding blood vessels in the neck warms the blood as it travels to the brain. Brown fat stored in the shoulders acts as an “internal heater” to keep the blood warm as it flows back to the heart and brain from the body’s cold extremities. This is the first line of defense against the cold.
Infants are born with a significant amount of brown fat. According to the Cleveland Clinic, about 2 to 5% of a baby’s body weight is made up of this fat. It is essential for our survival. The age at which brown fat is most abundant is during adolescence. However, as we age, our bodies produce less of it. This may help explain why children do not shiver in the cold like their grandparents or parents do. Older adults have less brown fat and also have less muscle – one of the important factors in generating heat.
