The protein-sparing effect of carbohydrate

Abstract

1. Measurements were made of the losses of nitrogen in the faeces and urine of sixty pigs of approximately 33 kg, given dietary regimens comprising twenty-nine combinations of fish flour (0-800 g/d) and maize starch (0-1200 g/d).2. The results were used to develop a generalized equation describing N retention as a joint function of N intake and starch intake.3. The protein-sparing effect of starch was exerted in all circumstances. It was greatest when protein intake exceeded 220 g/d but some effect persisted with protein-free diets. With a high protein supply, the increase in N retention per unit increase in dietary starch decreased from 36 mg/g with the first increment to 3 mg/g with the highest attainable starch intake.4. From the generalized equation the relationships between net protein utilization and protein concentration and food intake could be described as continuous functions. The equations may be of use in comparing the protein values of diets measured under non-standardized conditions.One of the difficulties of estimating nutrient requirements arises when theefficiency with which a nutrient is utilized is not constant. This difficulty seems to arise to some extent with every nutrient. In some instances it may be overcome for practical purposes by delineating a range over which a constant efficiency is a reasonable approximation. In studies of energy metabolism, for example, the convention has commonly been adopted of treating efficiency for maintenance and for growth as two constants, although this implies a distinct discontinuity at maintenance, whereas the over-all relationship may be better described by a single exponential equation (Blaxter & Boyne, 1970) with a continuously diminishing efficiency.This difficulty is particularly evident in estimating protein requirements, and it has long been realized that the efficiency of protein utilization is not determined simply by the amino acid composition of the protein but by the amount and composition of the diet in which the protein is supplied to the animal.It has been recognized that there are, in the absence of vitamin and mineral deficiencies, three major dietary variables which jointly determine the efficiency of protein utilization : the quality of the protein, the amount of protein given and the amounts of lipid and carbohydrate, the non-protein energy, given with it.Although these are the primary unconfounded variables, the effects on protein utilization of the amounts of protein and non-protein energy have usually been examined in terms of the variables derived from them : protein concentration (protein energy as a proportion of total energy) and daily food intake. Measurements of biological value (BV), or of net protein utilization (NPU) are by convention, therefore, made at a constant protein concentration, commonly 0.1.In more practical studies, there is a need to estimate the protein value of diets fed unaltered; in such instances a comparison of the protein quality of two diets can be made only if the effects on protein utilization of pr...

Growth hormone does not affect non‐insulin‐mediated glucose uptake in sheep

“…The plasma concentrations of insulin, GH, insulin-like growth factor 1 (IGF-1) and a.-amino nitrogen were determined using procedures described by Fuller, Weekes, Cadenhead & Bruce (1977), Johke (1978), Enright, Chapin, Moseley, Zinn, Kamdar, Krabill & Tucker (1989) and Ibbot (1974), respectively. The plasma concentrations of glucagon and non-esterified fatty acids (NEFA) were determined using commercially available kits (purchased from Eiken Chemicals Co. Ltd, Tokyo, Japan and Wako Chemicals Co. Ltd, Osaka, Japan, respectively).…”

Insulin, prolactin and thyroxine responses to feeding, and to arginine and insulin injections during growth in lambs

“…Plasma insulin concentrations were determined by radioimmunoassay using the method of Fuller et al (1977).…”

Effect of glucose‐dependent insulinotropic polypeptide on whole‐body glucose utilization in sheep

“…The plasma concentrations of insulin and a-amino nitrogen were determined using procedures described by Fuller, Weekes, Cadenhead & Bruce (1977) and Ibbot (1974), respectively. The minimum detectable concentration of insulin (defined as twice the standard deviation of the zero standards) was 1-5 mU 1-l, the intra-assay coefficient of variation was 8-5 %.…”