Feeding, blood glucose and plasma insulin of mice at dusk

Abstract

MOST omnivorous species exhibit a circadian rhythm of food intake. During one part of the day food is consumed at a rate in excess of immediate metabolic needs, and the surplus is stored to support metabolism for the remainder. Le Magnen and Devos¹, for example, have shown a predominance of lipogenesis in the night-time feeding period of the rat, and pronounced lipolysis during the day, when little food is consumed. A variety of metabolic adaptations exists to match this discontinuous pattern of food intake with relatively constant metabolic use of nutrient², but the question remains whether the hyperphagia at one time of day produces these changes or is a consequence of them. Le Magnen suggests the latter³, at least in the case of increased night-time meal frequency, and in models of feeding, such as that of Toates and Booth⁴, an increased rate of metabolic clearance of food at night is a considerable factor in promoting increased food intake. On the other hand, eating at a high rate clearly will promote metabolic changes, as bunching of the normal daily intake into a very short period will lead to increased weight gain⁵. A compromise possibility is that a greatly increased rate of feeding at dusk rapidly promotes metabolic changes subsequently favouring a high rate of feeding in the ways suggested by previous authors. The results reported here suggest that such a mechanism may operate in the feeding of mice, in that a great increase in feeding rate around the onset of darkness produces changes in carbohydrate metabolism which may both favour storage of energy and tend to increase subsequent food intake.