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.
Bringing Metabolism to a Simmer
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.
"Restricting calories simply by reducing the amount of food is difficult to sustain because people get hungry," said Dr. Dean Ornish, founder and president of the Preventive Medicine Research Institute and clinical professor of medicine at the University of California, San Francisco.
"If chronic calorie restriction is going to make people feeling miserable, deprived, or unhappy with life, it may not be worth it even if there could be solid evidence for it," said Keith-Thomas Ayoob, associate professor at the Albert Einstein College of Medicine in Bronx, N.Y.
"There is something to be said for quality of life and personal satisfaction. Maybe how long someone lives isn't the bottom line for everyone," Ayoob said.
Too Skinny on Evidence
Not everyone is convinced that caloric restriction lives up to its reputation as a life extender.
"I have seen a college professor who was doing CR a few years ago," said Dr. Donald Hensrud, associate professor of preventive medicine and nutrition at the Mayo Clinic College of Medicine in Rochester, Minn.
"He had biochemical evidence of malnutrition with abnormalities of various tests. In his case I have a tough time believing it would extend his longevity. I also believe that in him, as perhaps with others, it developed into a variant of an eating disorder," Hensrud said.
"Even in previously healthy individuals, one need only look at the spectrum of eating disorders typified by anorexia nervosa in order to demonstrate the potential risks of excessive caloric restriction," said Dr. Peter Pressman, assistant professor of clinical medicine at the University of Southern California in Los Angeles. "To suggest that caloric restriction is the answer to slowing the human aging process is at best simplistic and at worst seems quite misleading and dangerous to the public."
Others say that while whittling down the calories may help, it may be just one piece of the puzzle.
"The process of human aging is an extremely complex phenomenon," Pressman said. "Merely restricting calories in and of itself may be one contributor to certain aspects of metabolic rate, but it is likely not by any means the entire story."
"Longevity is about genetics, lifestyle, attitude, and possibly variables we don't yet know," said Connie Diekman, a registered dietitian and director of university nutrition at Washington University in St. Louis, Mo. "Changing one aspect of the equation can't guarantee longevity."
As the current obesity epidemic grows, it is unlikely that caloric restriction will become a widespread trend.
"CR is not an idea that will be widely embraced in a population gaining weight even as we speak," said Carla Wolper, research associate at the Obesity Research Center at St. Luke's Hospital in New York.
"After all, if we cannot get people to reduce their caloric intake modestly to lose weight, how will we ever get large numbers of Americans to reduce their weight below ideal?" Wolper said.