Meredith and Paul McGlothin have not found a potion or pill, but the two believe they have found a way to add years to their lives -- by eating significantly fewer calories.
"I'm trying to eat slightly less than my body would like during a course of a day," said Paul, a 57-year-old advertising executive. While most American men consume about 3,000 calories a day, he consumes just 1,900.
What the McGlothins are doing is not just a diet, it's called "caloric restriction" and it involves a radical lifestyle change. Most practicing CR cut calories by 10 percent to 30 percent, with the goal of living a longer and healthier life.
Animals Show More Energy with Fewer Calories
Caloric restriction is based on extensive animal research that has shown remarkable results. Monkeys and rats on the diet have much more energy than their counterparts that follow a regular diet, and rodents on the diet live about 30 percent longer than regular rats, research shows.
The McGlothins, who have been practicing caloric restriction since 1994, are sold on it, saying they are healthier and more energetic than when they started.
"I have more energy than I ever dreamed would be possible to have at any time in my life," Paul said.
And Meredith said that even if the diet does not significantly extend their lifespan, it is worth it now. "We are feeling better and we are able to work longer the way we want to," she said. "And we are hoping to add to our years of life, but even if it doesn't, it's healthy right now."
But How Healthy Is It?
Dr. David Katz, a nutritionist from Yale University and a "Good Morning America" medical contributor, says the jury is still out on how healthy caloric restriction is for humans.
"The verdict is not in in terms of longevity, and the reason for that is that it will take 120 years to see if people can live 120 years on this diet," Katz said. "Short term, it improves cardiac risk factors and it has the prospect of extending life."
Katz said that caloric restriction has not been compared to the American Heart Association diet or the Mediterranean diet in terms of health benefits, but is instead being compared to the typical American diet.
The diet does have certain side effects for most people, including being cold from lack of body fat, a reduced sex drive and loss of bone mass, which can lead to osteoporosis and breakage.
Fifteen Years of Low-Calorie Living
Lisa Walford, the co-author of "The Longevity Diet," which espouses caloric restriction, is 50 years old and has been on the diet for over 15 years now.
Walford stands at just under five feet tall and weighs 80 pounds -- about 15 pounds less than an average woman her height. She stresses caloric restriction is not the same as anorexia -- she eats throughout the day, but consumes only about 1,300 calories in foods like nuts, fruits and vegetables, and she is an avid practitioner of yoga.
The caloric restriction lifestyle has not been particularly difficult, she says.
"I was never in agony and it's different for each person, but I would have ample fruits and vegetables and eat as many of those as I wanted [when first adjusting to the diet]," Walford said. "After a while your body prefers healthy foods, prefers and recognizes foods that nourish you."
But Katz wondered if caloric restriction is even a realistic goal for the typical American, whose diet, he said, "stinks."
"This would probably slow aging, but it's unrealistic for a public that we can't even talk into moderation, let alone severe calorie restriction," Katz said.