The Long-term Effects of Meal-eating on Lipogenesis, Enzyme Activity, and Longevity in the Rat

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Abstract
Some effects of restricting access to food to a single, 2-hour period daily (meal-eating) over an extended period of time have been studied in rats. The in vitro lipogenic activity of epididymal adipose tissue was studied as well as the activities of glucose-6-phosphate dehydrogenase (G-6-PD), 6-phosphogluconate dehydrogenase (6-PGD) and malic enzyme in liver and adipose tissue. The average life span of meal-fed and ad libitum-fed (nibbling) rats was also determined. The previously reported adaptive changes induced by meal-feeding were apparent throughout the 18 months of study. The lipogenic activity of adipose tissue and the activities of the enzymes studied were significantly increased by meal-eating except for the activity of 6-PGD in liver. The lipogenic capacity and all enzyme activities were significantly influenced by time of experiment with most parameters showing a significant decrease with age. The rate of change with time was generally greater for the meal-fed rats than for the nibbling animals. A high degree of correlation was observed between lipogenic capacity and the activity of malic enzyme or G-6-PD in adipose tissue. A highly significant correlation was also noted between the activities of malic enzyme and G-6-PD in liver and adipose tissue of both meal-fed and nibbling rats. The average life span of meal-fed rats was significantly longer than that of nibbling rats (688 ± 24 vs. 587 ± 24 days). The possibility that the increase in life span may be due to the lower body weight, and presumably lower body fat, of the meal-fed rat is discussed.