While browsing sci.life-extension, I noticed two papers on calorie restriction (CR) that you might find interesting. Scientists are increasing our understanding of the mechanisms by which a calorie restricted diet brings impressive health benefits - and extended healthy and maximum life spans in most species - much more rapidly in this decade than the last. Perhaps this has as much to do with growing numbers of higher mammal and human studies as with the relentless advance of biotechnology.
This article addresses two questions: (1) 'can caloric restriction (CR) extend the life spans of all species of experimental animals', and (2) 'is CR likely to slow the human aging process and/or extend the human life span?' The answer to the first question is clearly 'no', because CR decreases the life span of the housefly, Musca domestica, and fails to extend the life span of at least one mouse strain. The answer to the second question is unknown, because human CR has not yet been shown either to increase or curtail the human life span. However, recent efforts to develop insect models of CR have been unsuccessful and/or relatively uninformative, so any insights regarding the relationship between CR and human aging are more likely to arise from studies of established, mammalian models of CR.
I think that the health benefits of human CR (in terms of resistance to age-related disease) are in the proven box now, with open questions regarding which populations benefit most or least. Life span effects seem probable, if only from a consideration of the reliability theory of aging. If you use CR to reduce cellular damage at the root of - or resulting from - age-related diseases, and aging is just an accumulation of this damage, then you should be slowing aging.
A few intriguing studies on inadvertent CR and human life span exist, as well as a number of scientific arguments against significant gains in maximum life span in humans, but nothing conclusive as yet. Don't expect "conclusive" to arrive any time soon either - for all of modern biotechnology, we're still stuck with extrapolation based on prevention of age-related disease, or waiting for people to die and counting the years. With that cheerful thought in mind, onto the next paper.
Calorie restriction (CR) retards aging in mammals. It has been hypothesized that a reduction in triiodothyronine (T3) hormone may increase lifespan by conserving energy and reducing free-radical production.
low serum T3 concentration was not associated with an increase in inflammatory cytokines in our CR subjects. In fact, markers of systemic inflammation, serum CRP and TNF-α concentrations, were low in our CR subjects. These findings are consistent with data from CR studies conducted in rodents and monkeys, which showed that CR caused a marked decrease in markers of inflammation and a reduction in serum T3 concentration. The combination of decreased serum T3 and reduced systemic inflammation could alter the aging process by reducing metabolic rate, oxidative stress and systemic inflammation
Long-term CR with adequate protein and micronutrient intake in lean and weight-stable healthy humans is associated with a sustained reduction in serum T3 concentration, similar to that found in CR rodents and monkeys. This effect is likely due to CR itself, rather than to a decrease in body fat mass, and could be involved in slowing the rate of aging.
The full PDF version of this paper is available. This human study confirms an observation of one distinct effect of CR in other mammals; this is now a more viable mechanism for further investigation, especially since the researchers seem to have eliminated the weight loss that accompanies CR as a possible cause. I find the reduced markers for inflammation more interesting than T3 levels, though that may be a bias resulting from the past few months of news on that topic - chronic inflammation is quite the bugbear in terms of its long-term effects on your health.
Clearly, calorie restriction is accomplishing a range of beneficial changes to biological processes across the board. Good stuff.