Your body contains two types of fat – white fat and brown fat. White fat is the kind you want to lose, because it can be bad for your health, especially if it gathers around your midsection.
Adipose tissue, or brown fat is good, because it keeps your body insulated. It takes an enormous amount of energy to burn brown fat to stay warm. Many slim people have a relatively high proportion of brown fat, while overweight people tend to have less brown fat.
Brown fat burns sugar and other fats to generate heat and is normally only activated when your body is cold. But a study from the School of Medicine at Nottingham University in the UK has looked at what happens to brown fat when you drink a cup of black coffee.