Dietary energy intake, hormesis, and health

The ability to adapt to varying levels of available energy in the form of food in the environment has allowed species to propagate and also thrive during times of energy surplus. However, in times when there is scant food available, similar evolutionary pressures have ensured that physiological systems can adapt to and utilize this food scarcity to their advantage. Considerable research has demonstrated that upon reduction of food intake, there are several beneficial effects upon cardiovascular, endocrinological, immune, and neuronal systems. Some of the effects of caloric restriction, however, tend to be exaggerated in many experimental cases due to biasing of overweight control subjects, yet reduction of total body weight still seems to engender beneficial effects for the individual. Some of the beneficial effects of caloric restriction are believed to arise from a reflexive response to the stress of reduced food intake. In conjunction with this is a similar hypothesis, known as hormesis, which proposes in a similar vein that other forms of stress, such as toxicological stress, can also engender a protective set of physiological responses that shields the individual from further stresses. This chapter discusses how these two theories of protective responses-caloric restriction and hormesis-share many overlapping properties.