Caloric Restriction Does not Slow Aging in Humans

From: Doug Skrecky (oberon@vcn.bc.ca)
Date: Tue Feb 24 1998 - 01:14:56 MST


    There has been some speculation that caloric restriction might be able
 to retard the rate of aging, and extend maximum human life span beyond
 120 years of age. (For example see the book "The 120 Year Diet" by Roy
 Walford)
    Recent evidence indicates that the anti-aging effect of caloric
 restriction, which has been documented in rodents, is not operative in
 humans.
    A low body-mass index does have a positive association with reduced
 mortality rates in humans. However recent research indicates that this is
 due to a negative association between BMI and physical fitness. After
 physical fitness is accounted for, there exists no further effect of BMI
 on mortality. See the following table from (International Journal of
 Obesity 19 Suppl: S41-S44 1995.

                     All Cause Death Rates
    BMI Fitness
                   Low Moderate High
    <27 52.1 28.6 20.0
   27-30 49.1 29.8 19.7
>30 62.1 18.0 (moderate & high together)

     While the above data indicate that the body mass index itself is not
 a primary driving factor for mortality in humans, the case it makes
 against caloric restriction exerting an anti-aging effect is not
 air-tight. What is needed is a false prediction from a postulated
 anti-aging effect of caloric restriction that could then be used in turn
 to falsify that hypothesis. I believe there exists one such prediction.
     Lower BMI is associated with reduced mortality in young and
 middle-aged humans. If caloric restriction retards the rate of aging and
 extends maximum life span in humans one must expect that a lower BMI
 would be significantly associated with reduced mortality in aged humans.
 If such an significant association is not found then caloric intake is
 not operative in modifying the rate of aging in humans and life spans
 beyond 120 will not be possible by reducing caloric intake.
     In humans over 84 years of age BMI has not been found to exert any
 significant effect on mortality. (New England Journal of Medicine 338:
 1-7 1998 & Arch Intern Med 157: 2249-2258 1997) Therefore since no
 association has been found between BMI and mortality in aged humans, then
 caloric restriction is not operative in modifying the rate of aging in
 humans.
     The fact that caloric restriction dramatically extends life span in
 mice, but not apparently in humans requires some explanation. Here is
 one. In mice caloric restriction is associated with torpor, which can act
 to reduce tumor growth. In C57BL/6J mice blocking torpor, by increasing
 housing temperature to 30 C reduced the increase in average life span
 associated with caloric restriction from 47% to just 4%. Since humans
 neither experience torpor, nor suffer from cancer to the degree that mice
 do the effect of caloric restriction in mice can not be generalized to
 include humans. For example in human centenarians only 4% die from
 cancer. By comparison cardiovascular disease accounts for 63% of deaths
 in those aged 95 and over. (Epidemiology 8: 501-504 1997) Thus it is
 cardiovascular disease and not cancer that is the major longevity
 limiting factor in humans.
     It is possible that potassium intake may be a major dietary modulator
 of human longevity. A high potassium intake has been found to reduce
 stroke associated mortality to zero. (New England Journal of Medicine
 316: 235-240 1987)



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