When you look at Joe Cordell, it's hard to imagine you're seeing someone who worries about counting calories.
At 5-foot-9 and 130 pounds, Cordell defies the stereotype of the overweight American, but this 48-year-old divorce lawyer is an experiment in progress.
He is one of a rarified group of Americans who practice caloric restriction (CR) -- a significant reduction in food intake that they believe leads to added longevity and health.
For the last five years, Cordell has cut his caloric intake by a third.
"If you'd asked me before I started CR if I could possibly enjoy a diet like that, I would have said no," he said. "Like almost every other American, I thought that variety was essential, but I know now that that's not true."
Caloric restriction is an intriguing idea -- and a controversial one.
Though studies show that restricting calories in mice and other animals leads to an extended life span, definitive results have not yet been seen in humans.
Yet, researchers like Dr. Luigi Fontana of the Washington University School of Medicine say caloric restriction holds promise -- as long as the regimen is followed properly, that is.
"Caloric restriction is not eating half a hamburger, half a pack of French fries, and half a can of one of these sugary beverages," he said. "It is eating a healthy diet, where you get rid of empty calories, and you eat lots of nutrient-dense food."
Fontana says the trick is to ensure that you still get 100 percent of your required nutrients every day, all while keeping additional calories to a minimum.
The principle is already being studied in rhesus monkeys, the closest thing to a human yet.
"The monkeys on CR look like they're aging at a slower rate and their health is staying better longer," said geriatric researcher Rick Weindruch, associate professor in the department of medicine at the University of Wisconsin in Madison, Wis.
He says he expects that some of the calorie-restricted monkeys will live 30 percent to 40 percent longer than their counterparts in the control group.
"We're starting to see clear differences in terms of how old the animal looks in the two different groups," he said. "Appearance is another indicator of biological age."
At Washington University, researchers are now seeking volunteers for a two-year study to determine the effects of caloric restriction in humans.
Despite the lack of definitive data in humans, researchers have a couple of ideas on how caloric restriction might lead to longer life.
"The theoretical basis for this is that burning fuel comes at a cost to an organism, just as it does to any vehicle," said Dr. David Katz, associate clinical professor of public health & medicine at the Yale University School of Medicine in New Haven, Conn.
"If you can meet the needs of body tissues while burning less fuel, you generate less heat, expose the body to fewer metabolic byproducts, and potentially reduce the net exposure to factors likely to damage DNA," Katz said.
"Calorie restriction in animals may induce certain proteins or enzymes, which may account for the longevity," said Dr. Sethu Reddy, chairman of endocrinology, diabetes and metabolism at the Cleveland Clinic in Cleveland.
Whether or not it works, one thing is clear: Such a drastic cut in calories is not a simple proposition.