|
Since Ponce de Leon’s fabled search for the
fountain of youth, the quest for a cure for aging has only accelerated.
As unprecedented numbers of Americans reach the age of 65, the scientific
community and the public at large has set its sights on more modern
(though perhaps just as futile) aging antidotes –namely hormones
and antioxidants. Both have proven to be ineffective, if not harmful.
Human Growth Hormone, for example, has been shown to decrease life
span, and like estrogen and progesterone, may prove to have detrimental
long term effects that we are as yet unaware of. The effects of
antioxidants (vitamins that may slow down aging) have also been
called into question. There is no evidence that their taking more
than what can be obtained from a healthy diet is at all beneficial.
Despite the millions of dollars funneled into aging
research in the past 30 years, the one thing that has proven to
extend life is something scientists have known about since 1915.
Remarkably, the answer to life extension seems to be as simple as
reducing the amount of food you eat.
Dietary Restriction: The Research
In 1935, McCay and his colleagues at Cornell University
reported intriguing data indicating that rodents fed on a 40% reduced
calorie diet experienced a mean life span increase of 30%. Since
then, numerous studies have shown that dietary restriction increases
not only mean, median, and maximum life spans, but that it also
reduces the incidence of most age-related diseases (including kidney
degradation and tumor incidence). Recent evidence even suggests
that dietary restriction may reduce age-related brain deficits as
well as the incidence of major neurdegenerative diseases like Alzheimer’s
Disease, Parkinson’s Disease, and epilepsy.
Do the protective aspects of reduced caloric intake
in rodent studies extend to higher order mammals and humans? Indeed,
accumulated evidence seems to point towards that conclusion. In
a study published by the National Institutes of Health, researchers
compared monkeys fed on normal diets with monkeys fed 30% less for
15 years. Like the rodents, monkeys on a reduced calorie diet lived
longer and avoided much of the typical age-related diseases. Although
time, money, and dietary restrictions have prevented such a long-term
study in humans, intriguing epidemiological evidence has found that
Parkinson’s and Alzheimer’s Disease is correlated with
increased caloric intake (more so then even body mass index or weight).
Dietary Restriction: The Effects
It seems almost counterintuitive to proclaim a near-starvation
diet as the secret to prolonging life. The immediate question that
comes to mind is why dietary restriction has these effects. Various
explanations have been embraced by researchers at one point or another
throughout the past 30 years, but the truth is that no one really
knows. At first, it was believed that dietary restriction extends
life span because it delays development or that perhaps, life extension
was due to a reduction of body fat. However, studies by McCay and
his colleagues indicated that mice who were put on a calorie restricted
diet after maturation fared just as well as mice who were put on
the diet just after weaning, thus disproving the claim that arrested
development was the cause of extended life spans. Studies also found
that reduced body fat did not play a causal role.
The next popular theory introduced the possibility
that the reduced metabolic rate (rate of fuel used per unit of body
mass) in mice eating a reduced calorie diet caused an increased
life span. The idea was that reducing the fuel intensity of metabolism
would slow down life processes and somehow cause living organisms
to “live more slowly”. Surprisingly, Mosoro and his
colleagues at the Center for Aging Research and Education found
that dietary restriction’s effect on aging need not be dependent
on metabolic rate; that in fact, the mice fed on a restricted diet
had the same metabolic rate in proportion to their body mass as
mice who were allowed to feed as they pleased.
While the results of that study are still considered
controversial, it has become clear that the effects of dietary restriction
are unlikely to be explained by one magic bullet explanation. In
the past few years, several new explanations have been brought forward.
They include the possibility that dietary restriction may provide
a general protective action against many agents capable of long-term
progressive damage like radiation, toxic substances, or high temperatures
(a view supported by evidence that protective heat shock proteins
are elevated in animals on low-calorie diets). Another possibility
is that the body must simply be more efficient in using calories
for self-preservation only (supported by evidence that cancerous
cells were the first to die in animals on low-calorie diets). These
theories, among others, are currently under intense investigation.
The Implications
Study after study has documented the remarkable effects
of reduced calorie intake in mammals, and all experimental and population-based
evidence seems to point to a similar effect in higher order mammals
and humans. It seems that a near-starvation diet may be the closest
thing we have to a pill for eternal youth. The question is will
Americans, known for their love of food, heed the compelling evidence?
Is cutting 40 to 50% in calories worth the extra years and protection
from disease? Until a pill is developed that can mimic the effects
of dietary restriction, it’s a question that every person
should seriously consider.
Sources
- “Anti-Aging Products, Do They Work?”, CBS News,
July 18, 2002.
- “A Diet To Stop Aging”. CBS News, December 15, 1999
- “Key to Long Life: Near-Starvation Diet?”. CBS Evening
News, July 8, 2002.
- Masoro, Edward J. The Mysteries of Aging: Is Diet a Contributing
Factor? http://www.acessexcellence.org/AE/AEC/CC/aging_background.html.
(23 July 2002).
- Mattson, MP, Chan SL, and Duan W. Modification of Brain Aging
and Neurodegenerative Disorders by Genes, Diet, and Behavior.
Physiological Reviews 82: 637-682, 2002.
- Ricklefs, Robert E. and Finch, Caleb E. Aging: A Natural History.
Scientific American Library: New York, 1995.
|
