"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.
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.