Evaluation of Protein in Foods: Xii. Effects of Calorie Restriction

Abstract

The effects of calorie restrictior~ on net protein utilization (N.P.U.) were studied with proteins of different nutritional value. When protein intake remained constant, reduction in the intake from 32 to 16 kcal per day resulted in a rapid decline in N.P.U. values. Increases in body weight were directly proportional to calorie intake per %g0J3 body weight. Even under conditions of marked caloric restriction, only 70-75y0 of the ingested protein was used for energy purposes, the rest evidently being used in essential anabolic activities. Studies on carcass co~npositicrn showed that animals on restricted calorie intakes tried to adapt through shifts in metabolism, arid utilized fat in preference to protein for caloric requirements. KN-4 metabolism in liver and muscle was influenced by energy and rotein intakes.i d e n the percentage of calories from protein remained constant, K.P.U. values were not markedly altered until the calorie intake reached the maintenance energy requirement s f 150 kcal per kg0.73 body weight. Below this point, N.P.U. values dropped sharply, the rate of decrease being greater for proteins of higher nutritive value. Differences in the nutritive value of proteins, as shown by their ability to satisfy protein requiremetats in protein-depleted rats, still existed even a t restricted intakes of calories.Wational Research Council of Canada Postdoctorate Fellow (196M6). I'erlnanent address:

Dietary components that regulate serum somatomedin-C concentrations in humans.

“…In the presence of adequate energy, therefore, optimal intake of protein appears to exert its greatest effect early in refeeding. The 2-d lag period may be the time required to reach a new steady state of improved protein absorption and/ or utilization, a common adaptation to low proteinadequate energy diets (21). Return of somatomedin-C toward control levels following this period might reflect the body's more efficient utilization of a subnormal dietary protein intake.…”