Caloric Restriction Does not Slow Aging in Humans

Doug Skrecky (
Tue, 24 Feb 1998 00:14:56 -0800 (PST)

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
Recent evidence indicates that the anti-aging effect of caloric
restriction, which has been documented in rodents, is not operative in
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
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)