> Doug Skrecky <firstname.lastname@example.org> wrote:
> Caloric restriction (CR) initiated in young rodents has been thoroughly
> documented to enhance longevity, but its efficacy when introduced at older
> ages has not been well investigated. Cohorts of 18- and 26-month-old male
> F344 x BN F1 hybrid rats were fed either ...
> This may have some relevance for humans as well. The scientific
> evidence does not support any significant direct effect of caloric
> intake on mortality of healthy adult humans.
This makes sense. 18+ month old rats are middle-aged (probably 40+ humans). Since it is likely that the processes by which CR works are a general slowing down of the wear-and-tear processes (DNA damage, oxidative stress, perhaps lower glucose levels, retarding the accumulation of damaged proteins, etc.) the later that you begin the CR, the less of an effect it will have. If you begin CR too late, any effects will be masked by the normal variability in longevity and will not be statistically significant.
All of the reports on the studies of primates undergoing CR (currently being done) are however consistent with the rodent studies and demonstrate the biochemical changes you would want to create given the various hypothesis regarding the various causes of aging.