The importance of "when" in calorie restriction-induced lifespan extension.

Abstract

Circadian rhythms are 24-h biological rhythms that are necessary for optimal health and daily variances in physiology and behavior. Circadian rhythms are maintained at the cellular level and are necessary for organ-specific functions. Cardiac tissue is no exception, and the heart maintains strong rhythms in gene expression as well as cellular metabolism throughout its lifespan [1] . Aging is associated with the gradual decline of circadian rhythms, raising the question of whether pharmacological or behavioral mechanisms that increase circadian robustness can slow the aging process. Time-restricted feeding is one mechanism to augment internal rhythms, decreased fat mass compared to ad libitum -fed mice); and (3) changes in circulating glucose in aged mice. Specifically, though insulin levels were similar in young AL and CR mice, circulating glucose was decreased in CR, suggesting increased insulin sensitivity. Upon aging, though all CR mice had lower insulin levels, even aged CR mice showed elevations in glucose, similar to AL groups. Thus, CR protects against insulin resistance across the lifespan.