Energy restriction, also known as caloric restriction (CR), is the most robust and reproducible means of reducing age-related diseases and extending life span in short-lived animals, but the effects in humans are unknown. Preliminary data from ongoing research with CR on long-lived nonhuman primates (rhesusandquirrel monkeys)also suggest potential health benefits—although it will take some years before final results become available and firmer conclusions can be reached regarding aging and life span.
Some epidemiologic and short-term human studies support CR-related health benefits. However, a role for CR in human aging is difficult to ascertain since human life span makes long-term investigations impractical and there are no universally accepted biomarkers to measure the rate of human aging. Whether CR (without malnutrition) affects human aging may be among the most significant unanswered questions in modern biogerontology. Yet we have few available human populations or studies that can address this question. Most human populations who have experienced low calorie intake have suffered from high mortality due to infectious diseases and malnutrition.
Studies of human CR volunteers are currently under way with promising early results, but will be unable to address longevity as an outcome Only one long-term (>30 years) epidemiologic study has linked CR to human longevity. This 36-year follow-up study reported a weak trend for lower all-cause mortality in healthy never-smoking Japanese–American men whose caloric intake was 15% lower than the cohort average, suggesting that those who maintained a modestly low energy intake (mean kcal/day 1882, range 1705–2061) in mid-life had the lowest late-life mortality risk. There was higher risk for mortality when caloric intake dropped below 50% of the group mean. These data are consistent with previous findings in animals, but much more study is required of healthy human populations with low caloric intake in order to understand the effects of CR on human aging and life span.
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