ODD as it may seem, people who need to lose weight or fight diabetes might benefit from some extra fat – if it is the right kind.

Unlike normal white fat, which stores the energy obtained from food, brown fat turns it into heat. This has led to the idea that it could be used as a weight loss aid.

Now Bruce Spiegelman at the Dana-Farber Cancer Institute in Boston and colleagues have shown that foreskin cells from mice can be changed into brown fat cells. When injected into mice, the cells burned sugar that would otherwise have been stored. A …