Twenty minutes on a treadmill will certainly help you fit into that one-size-too-small dress. But new research suggests that exercise may also help increase the production of nitric oxide, a substance that does a variety of important jobs in the body, perhaps none more valuable than to help prevent heart disease. "Nitric oxide does a variety of jobs," explains Dr. Jason Allen of Duke University. "It tends to be antiatherogenic, which means that it helps prevent your arteries from becoming clogged.