Does food restriction retard aging by reducing the metabolic rate?

Metabolic rate was determined by measuring O2 consumption in two groups of 6-mo-old male rats fed ad libitum (group 1) or maintained on a life-prolonging food-restriction regimen for 4.5 mo (group 2). These measurements were made continuously for 23.75 h under conditions nearly identical to those of the daily life of the rats. The metabolic rate per kilogram lean body mass was the same for both groups, a finding contrary to the hypothesis that food restriction retards the aging process and prolongs life by slowing the metabolic rate per unit of metabolic mass. This and our previous work strongly suggest that the classic views of the action of food restriction on aging must be re-evaluated because retardation of the aging process can occur without the restriction of calories or any other nutrient per unit of lean body mass. The long held belief that reducing food intake lowers the metabolic rate per unit of metabolic mass may be true in short-term dietary programs but appears not to be true when a significant portion of the life span is involved.