Mark Mattson, 52
(COURTESY NATIONAL INSTITUTE ON AGING)
Chief, Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health
What he does: Limits calories to around 2,000 per day. Always skips breakfast, and lunch on Mondays, Wednesdays, and Fridays. Every evening he grazes on fruit, veggies—and a bowl of oatmeal—in addition to dinner.
Why: Research by Mattson and others suggests that restricting calories (and occasionally fasting) can stimulate "adaptive stress response mechanisms" in the body, which may boost its resistance to injury and disease. Doesn't he get hungry? "I think it's actually good to be hungry," says Mattson, who is 5 feet 9 inches tall and weighs less than 130 pounds. He doesn't let hunger derail his exercise routine, either. During high school cross-country season, even on days he has one meal, he'll run 6 to 9 miles with the team he coaches.
[Consider why occasional fasting might be a good idea.]