The metabolic basis of dual periodicity of feeding in rats

Abstract

This article examines how the depletion and replenishment of various energy stores give rise to periodic eating and how constant body-energy levels are maintained over time.Measures of the energy expended throughout the 24-hour feeding pattern in rats indicate that two different energy stores (one of small capacity and one of large) determine two superimposed feeding periodicities: one from meal to meal (prandial), the other from day to night (nycthemeral). The article reviews how experimental overrepletion or overdepletion of gastrointestinal content, blood glucose, or body fats affect food intake. These data suggest that gastrointestinal content determines both meal size and meal-to-meal periodicity. Other evidence indicates that glucose uptake rate in tissues, which is modulated by fat synthesis and fat mobilization, affects the periodic onset of feeding and the difference between nocturnal and diurnal postprandial satiety.There follows an examination of the neuroendocrine bases for the interacting mechanisms governing energy input and output balance and of the role of the ventromedial hypothalamus in body-fat regulation and the lateral hypothalamus in feeding.

Adrenal Steroid Receptors: Interactions with Brain Neuropeptide Systems in Relation to Nutrient Intake and Metabolism

“…The process of maintaining the body's nutrient stores requires moment-to-moment alterations in both ingestive and metabolic processes. These complex functions are performed through the brain, via its neurotransmitter and steroid receptor systems, which organize and integrate an array of signals from within the central nervous system as well as from circulating hormones, the peripheral nervous system, and the environment (25,102).…”

“…Depending on energy requirements, nutrient consumption leads to oxidative metabolism for immediate use and/or to the storage of these nutrients in the body for later utilization. The daily rhythm of energy balance is generally characterized by a positive energy state during the active (dark) period, when there is increased intake and storage of nutrients (102,107). This is in contrast to the negative energy state, which develops over the course of the inactive (light) phase as a result of little feeding and increased breakdown and utilization of the body's nutrient stores (102,107).…”

“…Feeding is characterized by a bimodal distribution, with peaks during the initial and final 3-4 h of the dark period (102,106). These bimodal bouts of feeding have different characteristics and, in addition, are associated with different metabolic processes.…”

“…While not as strictly regulated as protein intake, recent evidence indicates that daily ingestion of carbohydrate may be physiologically controlled, possibly in relation to dietary protein (1 15, 116). Moreover, the maintenance of carbohydrate stores, through both ingestion and metabolism, is found to be particularly critical at a specific time of the light/dark cycle, towards the end of the inactive period, when nutrient reserves are at their nadir, and energy demands are rapidly increasing (102,107).…”

“…In contrast to protein and carbohydrate, there is little evidence that fat ingestion is closely regulated from day to day. Alterations of dietary fat content do not lead to the maintenance of constant levels of intake (102,104,105), and, in fact, access to a high-fat diet may actually lead to excess consumption of this nutrient (132). Consequently, dietary fat is a primary contributor to the development of obesity, pr.oducing less satiety and greater total intake, fat deposition and positive energy balance relative to the other major nutrients (132)(133)(134)(135)(136)(137).…”