Brown (and it's related beige counterpart) fat is packed with mitochondria which helps it burn fatty acids and calories rather than storing them. In contrast, white fat acts as a fat storage depot and is the principal form of fat found in obese individuals. As one ages, the ratio of brown + beige/white fat decreases with the highest ratio seen in newborns and young adults. Brown and beige adipose tissue can be recruited by cold temperatures and there are some reports that habitual exercise may increase brown fact activity.
I'm curious if anyone knows of any studies looking at the ratio of brown + beige/white fat volume in sedentary vs. endurance athletes? I am aware of several studies examining the activity of brown and white fat in athletes vs. non-athletes - but what about whole body distribution of these various types of fat tissues.