Nutrition and the extremes of life: dilemmas and enigmas of advanced old age.

Pre-term infants born four months before term have a very low birth weight; in an evolutionary sense, they were never 'meant' to survive through the evolutionary period preceding the technological age. In the same way, evolution failed to contemplate survival to ages 50, 60, 70 and beyond. Because peak reproductive performance comes before the vagaries of a given individual's survival is determined, and the fact of that survival conveys no advantage to disseminating the genetic make-up, natural selection cannot select for advantages related to longevity. Moreover, in the larger context of species survival and biodiversity, the crowding of the human ecosphere with older persons would seem to have had more liabilities than assets over evolution. We cannot learn from nature how to feed and nourish the oldest old. The lessons, if any, would be cruelly averse to our humanitarian values. However, we do have values and they guide us to the goal for quality of life for the assorted conditions of the extremely old. The choices are laissez faire or laissez aller. If we are ignorant about how to achieve the goals, perhaps the 'first do not harm' principle should be operative. Should we decide that prescription of diet and adjustment of nutritional stores are required, hypothesis-based research to provide evidence-based practices is required. We may be facing a true Heisenberg principle. The fact that ageing leads to the greatest heterogeneity among individuals complicates the generation of universal principles for prescriptive actions. Another quandary could be the fact that insufficient individuals within the age groups of interest are available for outcome research in any given area to provide statistically robust findings. Shifting once again to the lowest extreme of human survival, we know that what is good for the full-term infant is not the formula for the 600 g premature neonate. Failing to heed the distinction can be lethal. My suspicion is that what is good dietary practice for the younger adult is also not what is best for octogenarians. I would predict that a new intergenerational confrontation is in the offing as we recognise and raise the issues of alimentation of the extremely old. It is the tyranny of the preventive regimens of assorted guidelines to be imposed across the whole population that may exacerbate the tension between young and old, although the young's consuming a more healthful diet will presumably allow more of them to eventually reach the status of advanced age, and hopefully with greater health, vigour and function.