When we are born our body composition is 90% fat. Though it is very cute and soft when a baby has that much fat. The fat provides insulation and helps regulate the babies temperature. Inside the body there are grape like clusters of fat that are grouped together around the vital organs and heart. More is found in the thoracic region of the body. This fat is known as brown fat. Unlike white adipose fat, brown fat has a cluster of capillary beds attached to them providing blood and nutrients. They have mitochondria allowing for oxidation. Brown fat is believed to be a primal fuel system that helped keep primitive man warm during the cold months. When the baby develops more muscle brown fats burning ability reduces. We wear many layers of clothes and this provides the body with heat reducing the use of brown fat even more. Remember as a kid your mother would always tell you to put your coat on before going outside. Little did mom know that the body was utilizing its brown fat storage to keep the body warm. Sometimes when my kids are playing I can feel the heat radiate from their body. It is more pronounced behind the neck down toward the mid thoracic region where brown fat is more concentrated. Their brown fat is fired on.
As we get older we tend to turn the heat up in the house when we are cold or put on more layers of clothing. This only dampens the brown fat effect. You can restart the brown fat phenomenon by keeping the thermostat down to a cooler temperature in the house and wear less clothing, a tee shirt rather than a sweater. The body will begin to realize that there is a need to heat up internally and brown fat will start up. Actually it is very healthy to keep the temperature cooler rather than hotter. The body burns more calories when it is trying to warm itself up. Brown fat actually oxidizes adipose fat. Brown fat is a primal fuel system but can still be useful today if you activate it. It is just another way to burn off excess fat without losing muscle.