Promising biotechnologies currently in development will eventually make human aging obsolete and particular diet prettymuch irrelevant to health. Cellular and molecular damage will be easily and cheaply repairable. Once we can achieve longevity escape velocity, human beings can live youthful healthy lives indefinitely even on a delicious SAD.
A good pubmed summary of this prospect from de Grey et al. is here:
Aging is a three-stage process: metabolism, damage, and pathology. The biochemical processes that sustain life generate toxins as an intrinsic side effect. These toxins cause damage, of which a small proportion cannot be removed by any endogenous repair process and thus accumulates. This accumulating damage ultimately drives age-related degeneration. Interventions can be designed at all three stages. However, intervention in metabolism can only modestly postpone pathology, because production of toxins is so intrinsic a property of metabolic processes that greatly reducing that production would entail fundamental redesign of those processes. Similarly, intervention in pathology is a "losing battle" if the damage that drives it is accumulating unabated. By contrast, intervention to remove the accumulating damage would sever the link between metabolism and pathology, and so has the potential to postpone aging indefinitely. We survey the major categories of such damage and the ways in which, with current or foreseeable biotechnology, they could be reversed. Such ways exist in all cases, implying that indefinite postponement of aging--which we term "engineered negligible senescence"--may be within sight.
Optimistic forecasts have this technology being largely available in just a few decades. Some alive today may live 100s of years or more. Assuming this optimistic scenario obtains, would you continue to eat paleo (or "primal" or "archevore" or "realwholefoodstm" or whatever you call it) if you could easily remedy any biological damage from sugar, wheat, peanut butter, BBQ sauce, etc. etc. and do so continually for centuries while maintaining youthful health?