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Health Protocols

Caloric Restriction

Caloric Restriction in Humans and Increased Lifespan

Assessing the effects of dietary interventions on human lifespan is a difficult endeavor; with average life expectancies of 75 and 80 years for men and women, respectively,14 any prospective study would likely necessitate several generations of researchers to carry out. Therefore, human aging studies must rely on surrogate measures (biomarkers) of aging. Reduced body temperature and lowered fasting insulin levels are robust markers of CR and slowed aging in rodents and rhesus monkeys.15

Dehydroepiandrosterone sulfate (DHEA-S), which declines in both rhesus monkeys and humans during normal aging, may be important in health maintenance and may serve as another potential longevity marker.16 DHEA-S, a product of the adrenal glands and the most abundant circulating steroid hormone, serves as the precursor to the sex steroids (androgens and estrogens). Increased DHEA-S levels in monkeys on CR are associated with survival.17 Similarly, data from the Baltimore Longitudinal Study of Aging (BLSA)18 suggest long-lived humans exhibit some of the same physiological and biochemical changes that accompany CR in animals. In the study, human survival rates were highest in those with low body temperatures, low levels of circulating insulin; and high DHEA-S levels.19

While there is yet no direct evidence of human lifespan extension by CR, there has been limited observational and clinical data that suggests a connection. In the 1970s, the Japanese island of Okinawa was reported to contain up to 40 times as many centenarians as other Japanese communities, which was suggested to result from CR (The caloric intake of adults and children in Okinawa was 20% and 40% lower than their mainland counterparts, respectively).20 Two decades earlier, a small study revealed that 60 healthy seniors receiving an average of 1,500 kcal/day for a period of three years had significantly lowered rates of hospital admissions and a numerically lowered death rate than an equal number of control volunteers.21