LOS ANGELES, Aug. 29-Severe caloric restriction may significantly extend the lives of mice and other small critters, but a starvation diet won't produce a similar payoff for bigger animals, like human beings, a study here suggests.
"Primates are not simply big rodents," evolutionary biologists wrote in the August issue of Aging Research Reviews.
A lifetime of reduced caloric intake, consuming on average about 1,500 calories per day, would result in only a 7% extension in human lifespan, according to a mathematical model.
The tradeoff is small, and it can come at a price, reported John Phelan, Ph.D., of the University of California at Los Angeles and Michael R. Rose, Ph.D., of the University of California at Irvine.
"To undergo decades of caloric restriction, suffering chronically reduced fertility and increased hunger, for the sake of a much smaller proportionate increased in longevity than is seen in rodents seems unappealing and ill-advised," they wrote. "Caloric restriction is unlikely to be a panacea for human aging."
Caloric restriction became something of a fringe fad after research showed severe dieting extended the lives of rodents, fish, cockroaches, ticks, water fleas, spiders, mollusks and protozoa.
For example, organizations such as the California-based Caloric Restriction Society advocate that caloric restriction could help humans exceed estimated life expectancies.
But Drs. Phelan and Rose emphasized that the primate model is quite different from that of a mouse.
According to the researchers' mathematical model, consuming only 1,500 calories a day led to a 7% longer life for humans, whereas comparable caloric restriction in rodents resulted in 67.5% longer life, or 10 times that of the benefit to humans, the investigators wrote.
Although there is evidence in animal models indicating caloric restriction works, there is no proof this could be true in humans. "Longevity is not a trait that exists in a vacuum," the researchers cautioned. Starvation may help extend the lives of rodents because it reduces fertility, the investigators explained, thereby reducing the biological stress of countless matings and pregnancies. Humans reproduce more slowly, and caloric restriction may not have as pronounced an effect in people, they said.
To demonstrate that the benefit of caloric restriction would be minimal in humans, Drs. Phelan and Rose used a mathematical model.
First, they noted that in Japan, the average male adult consumes about 2,300 calories per day and lives to be on average 76.7 years. This population fell in the middle of a longevity and caloric intake spectrum.
Then they looked at either side of the spectrum. On one side were males living on the island of Okinawa, an area where residents are known for their simple diet and longevity. The researchers estimated male Okinawans consumed about 17% less than the average Japanese male, yet the average age for an Okinawan male was 77.5 years.
On the opposite side of the spectrum were Japan's Sumo wrestlers, who consume about 5,500 calories per day and live to be about 56 years old.
If both the Okinawans and Sumo wrestlers cut their caloric intake to 1,500 calories per day, "the best possible mean human life spans obtainable from caloric restriction are 81.9 years (for the Okinawans) and 78.3 years (for the Sumo)," Drs. Phelan and Rose wrote.
When looking at just the Sumo wrestlers, who appeared to have the greatest potential benefit, the maximum extension in life span came only to 7%.
However, when applying comparable caloric restrictions to mice models, this added up to be a 67.5% benefit in extending lifespan.
Thus, this analysis predicts an "approximately 10 times greater effect of caloric restriction on rodent longevity than on human longevity," the researchers concluded.
"If our quantitative analysis is to be taken at face value," the researchers concluded, "the quantitative benefit to humans from caloric restriction is going to be small."
http://www.medpageto...trition/tb/1626
Why dietary restriction substantially increases longevity in animal models but won’t in humans
Caloric restriction (CR) extends maximum longevity and slows aging in mice, rats, and numerous non-mammalian taxa. The apparent generality of the longevity-increasing effects of CR has prompted speculation that similar results could be obtained in humans. Longevity, however, is not a trait that exists in a vacuum; it evolves as part of a life history and the physiological mechanisms that determine longevity are undoubtedly complex. Longevity is intertwined with reproduction and there is a cost to reproduction. The impact of this cost on longevity can be age-independent or age-dependent. Given the complexity of the physiology underlying reproductive costs and other mechanisms affecting life history, it is difficult to construct a simple model for the relationship between the particulars of the physiology involved and patterns of mortality. Consequently, we develop a hypothesis-neutral model describing the relationship between diet and longevity. Applying this general model to the special case of human longevity and diet indicates that the benefits of caloric restriction in humans would be quantitatively small.
http://www.sciencedi...fc2d5db0d7f2fdf
