Fig. 1. Experimental approaches used to improve fitness and promote health span.

Description of different feeding regimens, their macronutrient balance, and feeding time during a 24-hour period. The feeding time represented in the day-night diagrams refers to eating time in humans and nonhuman primates. Mice undergoing a CR regimen tend to finish their food allotment quickly, self-imposing a continuous form of TRF. In human studies, people voluntarily reduce their food intake and mostly adhere to a three-meals-per-day schedule. Mean life-span extension is documented for all the treatments in the species depicted in the box, whereas maximum life span is only achieved after CR and IF or PF.