A scientist turned venture capitalist, Tartaglia is betting on the newest science in this area: brown-fat biology. Unlike white fat cells, which get their name from the excess lipids they store and whose relatively few mitochondria transfer energy from the lipids and sugars to the energy-storing molecule ATP, brown fat cells’ many mitochondria contain an “uncoupling protein” that allows them instead to release the energy from sugars and lipids as heat—to warm hibernating animals, for example. Researchers think that by increasing the numbers of brown fat cells in adults, or by activating those that already exist, they will be able to help people burn calories, shedding extra pounds as a result.