Eating time modulations of physiology and health: life lessons from human and ruminant models.

Tissue nutrient supply may be synchronized with endogenous physiological rhythms to optimize animal and human health. Glucose tolerance and insulin sensitivity have endogenous rhythms that are not essentially dependent on food type and eating. Human glucose tolerance declines as day comes into night. Based on such evolutionary findings, large evening meals must be avoided to reduce risks of visceral adiposity, diabetes, hypertension and related cardiovascular complexities. Ruminants as extremely important food-producing livestock have evolved to ruminate mostly overnight when little grazing occurs, and when rumen reaches a larger volume and fermentation capacity. As such, eating time (e.g., evening vs. morning) will alter postprandial and diurnal patterns of food intake, rumen and peripheral metabolites production and supply, and milk and meat production efficiency. Most recent discoveries suggest that eating time modulates postprandial intake and metabolism patterns in non-grazing lactating cows. Eating rate and absolute intake can increase by evening vs. morning feeding in dairy cows. Evening feeding increased postprandial rumen volatile fatty acids (VFA) peak, and surges of blood insulin, lactate and beta-hydroxybutyrate, and induced a peripartal decline in blood glucose. As a result, milk fat and energy production were increased. While being unfavorable to human health, evening and night feeding have proved beneficial to ruminants. These findings establish a differential chronological basis for food intake and nutrient metabolism in man and food-producing animals. Eating time is a major external cue and a feasible life strategy that affects production and health physiology.