Tantalizing evidence exists that cutting calories by 20 percent helps monkeys, who are close relatives, to live longer, healthier lives. And, in one nonscientific program, adults are reducing their caloric intake by as much as 30 percent in the hope of living healthfully (if not too happily) for 100 years or more. What if scientists can figure out just what combination of genes and proteins extends the lives of so many other living things that don’t fully give in to their hunger? In that case, it might be possible to come up with drugs that would let us have our cake and eat it, too. David Sinclair and his colleagues at Harvard Medical School have cooked up some delicious clues to how this might happen. They found an enzyme that makes yeast cells live longer simply because they think they are starving. The enzyme catalyzes a marked increase in the activity of a protein known as Sir2, which in turn promotes yeast survival by reducing events associated with cell death. With the help of the enzyme, called Pnc1, yeast cells live 70 percent longer. If humans lived that much longer, their average life span would increase from 80 to 136 years. Humans aren’t yeast, or worms, flies, or rats, but they do have a version of Sir2 called SIRT1.