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Adipose tissue is the medical term for body fat. There are two main types of body fat: brown and white. When compared to white adipose tissue (WAT), brown adipose tissue (BAT) has more cytoplasm and mitochondria within the cell itself and a greater number of capillaries that provide more oxygenated blood to the tissue. The greater density of the tissue causes it to sometimes be mistaken for glandular tissue during medical tests.
It is the increased number of mitochondria that is actually responsible for the darker color of brown adipose tissue. This is because mitochondria have a high iron content that tints the fatty tissue to its characteristic brown or reddish color. Mitochondria are the energy producing parts of a cell that are responsible for generating adenosine triphosphate (ATP), which is then used as chemical energy by the cell. The increased numbers of mitochondria allow brown adipose tissue to play an important part in the body’s thermo-regulation.
When the human body’s core temperature decreases because of exposure to cold, which is called hypothermia, the body will try to raise its internal temperature by shivering. This process uses energy and creates heat. However, this tissue is capable of producing additional heat without requiring the body to shiver. It is this process, non-shivering thermogenesis, which protects hibernating animals and prevents newborn infants from shivering just after birth.
As much as 5% of a newborn’s body weight can be made up of brown adipose tissue. Scientists continue to investigate whether this tissue actually disappears during normal growth or if it becomes part of the skeletal muscles around the upper back and shoulders. Some studies have found the presence of this tissue in the neck and chest regions in adults. The heat being produced by this tissue can actually be seen with the aid of an infrared camera, also known as a thermal camera, allowing scientist to identify it. There also have been some rare cases in which tumors have formed from the tissue when it has failed to disappear or become part of the skeletal muscle.
Scientists also are working to understand the role brown adipose tissue might play in weight management. This research has shown that brown adipose tissue can use energy stored in white adipose tissue to create heat, thus lowering the total amount of white adipose tissue in the body. The study also revealed that obese individuals had lower amounts of this tissue than non-obese persons, indicating that brown adipose tissue might play an important role in maintaining a healthy weight.