Evaluation Of Protein In Foods Xii. Effects Of Calorie Restriction

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 sf 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
at restricted intakes of calories.