Why does calorie restriction reduce the rate of aging?

Calvin Harley charley at MCMAIL.CIS.MCMASTER.CA
Fri Aug 21 15:51:48 EST 1992

I can't answer Bradbury's general or specific questions, but I would like
to suggest that maybe the way we think about the interaction between
caloric intake and lifespan is backwards. Perhaps it is not that caloric
restriction reduces the rate of aging (or increase maximum longevity), but
rather that ad lib consumption of food increases morbidity and mortality.
I think this is more than a philisophical point. I favour one or more
forms of the antagonistic pleiotropy (Williams' 1957) theory of
senescence, which leads one to predict that many (perhaps thousands) of
genes have co-evolved to dictate a certain maximum genetic lifespan. It
thus is unlikely that a single alteration in lifestyle or diet or a "pill"
will have a dramatic effect on the genetically determined lifespan. Maybe
the lab animals on which the caloric restriction theory has been tested
all have curtailed "normal" lifespans because of ad lib feeding. Maybe
first-world humans are in the same condition. If 120 y is our genetic
maximum, then I would predict that CR would allow more of us to live closer
to 120 y, but it would not push the tail of the curve out to 150-200 y or
more, as some have predicted. None of what I have said undermines the
usefulness of studying CR or ad lib feeding as a model to study factors at
various levels which affect aging. I just think the "experimental system"
is ad lib feeding and so-called caloric restriction may be closer to the
normal "control".

Calvin Harley
Dept. of Biochemistry
McMaster University
Hamilton, ON

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