Brown fat, also called brown adipose tissue, is a special type of body fat that is turned on (activated) when you get cold. Brown fat produces heat to help maintain your body temperature in cold conditions. Brown fat contains many more mitochondria than does white fat. These mitochondria are the "engines" in brown fat that burn calories to produce heat. Brown fat has generated interest among researchers because it appears to be able to use regular body fat as fuel. In addition, exercise may stimulate hormones that activate brown fat. It's too soon to know whether brown fat's calorie-burning properties can be harnessed for weight loss. In the meantime, be sure to include physical activity in your weight management plans.