Diurnal pattern of protein and energy metabolism in man

Abstract

Rates of synthesis and breakdown of body protein and oxidation of leucine were measured in six obese subjects by constant intravenous infusion of (1 14C)leucine for 24-hr periods. During the night, when no food was given, the rate of whole body protein synthesis was 67% of the rate observed furing the day, when food was given hourly. By contrast the rate of body protein breakdown remained constant over the full 24 hr. This resulted in the immediate deposition of about 30% of the protein intake during the day, whereas the remaining 70% was immediately oxidized. At night the rate of protein oxidation fell to only 38% of its daytime value. The rate of oxygen consumption also decreased at this time so that the contributon of protein oxidation to total energy expenditure fell from 27% during the day to 13% at night. These changes reflect the normal, discontinuous pattern of food intake and the need during feeding to store protein in tissues for use in subsequent periods of fasting.

Effects of dietary fat on postprandial substrate oxidation and on carbohydrate and fat balances.

“…But it is established that protein oxidation is greater during the day than during the night (21), which indicates that the use of amino acids for energy production is related to availability, as in the case of carbohydrate.…”

Adaptation of protein metabolism in relation to limits to high dietary protein intake

“…It was also shown that these changes took place very quickly, already being apparent on the ®rst day after the change in diet, with smaller changes thereafter (Garlick et al, 1980a). The rapidity of these changes, and a growing awareness that rates of protein turnover are not constant even within a single day, undergoing cycles of protein deposition during feeding and loss during fasting (Garlick et al, 1973(Garlick et al, , 1980bClugston & Garlick, 1982), emphasized the need for methods of measuring protein dynamics over short periods of hours, rather than the days required with the [ 15 N]glycine method. Although a more rapid technique with [ 15 N]glycine was developed (Fern et al, 1981), the primed constant infusion of [1-13 C]leucine (Matthews et al, 1980;Motil et al, 1981) has proved the most useful.…”

Effects of acute and chronic level of protein supply on metabolic leucine utilization in growing and mature rats

“…Several studies have investigated the effect of feeding on metabolic leucine utilization in humans (Garlick et al 1980;Motil et al 1981;Clugston & Garlick, 1982;Rennie et al 1982;Hoffer et al 1985;Melville et al 1989). In these studies the specific activity of plasma leucine (or ketoisocaproate) and breath CO, was measured in the steady state, in order to calculate leucine flux and leucine oxidation.…”

“…1990). Feeding repeated small meals has been observed to increase the percentage of leucine flux subjected to oxidation in a steady state by about 1.5 times (Garlick et al 1980;Motil et al 1981 ;Clugston & Garlick, 1982;Rennie et al 1982;Hoffer et a/. 1985;Melville et a/.…”

“…From recent IAA oxidation studies in the fed state at different levels of IAA intake in adult humans, it was concluded that current estimates of IAA requirements were too low (Young et al 1989). There is no consensus, however, about the metabolic basis for protein and IAA requirements (Millward & Rivers, 1988;Millward et al 1991 ;Young, 1991).Several studies have investigated the effect of feeding and fasting (Garlick et a[. 1980;Motil et al 1981 ;Clugston & Garlick, 1982;Rennie et al 1982; Hoffer et al 1985;Melville et al 1989) and the level of chronic protein supply (Millward et al 1991) on metabolic leucine utilization.…”