Physiology of the hormetic effect.

Beneficial (hormetic) effects of ionizing radiation have been largely ignored in developing radiobiological theory, chiefly because a suitable explanatory hypothesis is lacking. Examination of the relevant literature has revealed that food restriction effects in animals resemble those of low-level, low-LET, whole-body ionizing radiation exposure (without food restriction) in two major respects: increased longevity and change in the variance of longevity. These physiological changes can be interpreted as resulting from alteration of the "steady-state" flux of oxygen radicals which affect the endocrine balance.

Food restriction, ionizing radiation, and natural selection.

It is proposed that the allocation of energy in the animal body is modulated automatically by the endocrine system which through one or more centers responds directly to the oxygen radical flux (or an appropriate surrogate) derived from the metabolism of the ingested food. It is also proposed that energy to maintain temperature as well as reproduction and the reproductive capacity are the main sources of oxygen radicals that may be the direct cause of aging. Energy used for gathering food, resisting predators, play (i.