Why we get old and die, and what to do about it
Evolution arranges for members of a species to do the work of reproduction and then to get out of the way, that is, die, in order to not compete for resources with their offspring. Aging is the mechanism used by evolution to ensure a rapid death in the wild, once the reproductive phase is over, for sexually reproducing species. However, when food is scarce, longevity increases and reproduction slows down, awaiting the return of good times. Insulin is a signal that early in life promotes growth and reproduction but later on promotes aging, by its action of suppressing those repair and replacement mechanisms in each cell which counteract the wear and tear that is aging.
When food is plentiful, so is circulating insulin, and individual members age and die as programmed by evolution. When dietary carbohydrates are high, insulin levels go above normal, and aging proceeds more rapidly, with higher rates of type 2 diabetes, cancer, cardiovascular disease, and dementia. Eating less, i.e. caloric restriction, extends longevity in many species, and suppresses insulin levels. Substances which lower insulin levels, such as metformin, aspirin, and coffee, and other compounds which interfere with the insulin signalling pathway, such as rapamycin (an immune suppressant) and resveratrol (found in red wine), have also been found to decrease mortality. Restricting dietary methionine, an essential amino acid, may also increase longevity, again perhaps through insulin signalling.
The text of the talk, which was given to the Westmount Rotary Club on 2017-6-14, is here. The addendum, which gives practical advice, is continually being revised and updated, and the updates are posted here.
For the science behind this hypothesis, with references, see [this document].