Changes in Body Weight and Composition of Adult Nongravid Female Rats Deprived of Dietary Protein

Seventy-six young adult nongravid female rats of the Carworth strain were used in two experiments to study the effect of dietary protein deprivation on body weight, feed consumption, body composition and serum protein concentration. Semi- purified diets containing glucose, corn oil, vitamins and minerals with or without casein (protein-free = PF, 14% casein = C) were fed ad libitum in both experiments to rats caged in individual wire-bottom cages. Feeding the PF diet for up to 26 days resulted in a continuous weight loss over the entire period. The average loss in body weight as a percentage of initial weight of PF rats in experiments 1 and 2 was 32.9 and 25.7, respectively. Weight loss during 9 days in rats fed the PF diet was restored within 8 days following transfer to the C diet. Feed consumption was reduced only moderately by the PF diet, suggesting a large loss of ingested calories by excretion or metabolism to carbon dioxide and water. Body composition data supported this and indicated a greater relative loss of body energy than of body protein in PF rats. Blood serum protein concentration was reduced moderately (P < 0.05) in rats fed the PF diet. The absolute loss of serum protein may have been greater than suggested by the concentration if it is assumed that there was a reduction in blood volume associated with the observed weight loss. Blood serum protein concentration therefore does not appear to be as sensitive an index of protein nutrition in the adult as in the young animal. Final body energy, protein and water content were less in PF rats than in C rats in experiment 2 by an average of 176.5kcal (36%), 10.9 g (23%) and 41.7 g (28% ), respectively. Energy concentration (kilocalories per gram dry weight) was 11% greater in C than in PF rats (5.8 versus 5.2 kcal/g). These data indicate that the adult female nongravid rat can survive a loss of at least one-third of body energy and one-fourth of body protein induced by protein deprivation without developing severe hypoproteinemia, emaciation and edema. The effect of dietary protein depriva- gravid animals. The experiments reported tion on reproductive performance has been here describe the effects of protein depri- studied extensively in the rat (1-3) but vation on body weight, voluntary feed con- only limited data are available on its effects sumption, serum protein level and body on the nongravid female rat. Protein dep- composition of adult nongravid female rats, rivation reduces the incorporation of amino EXPERIMENTAL PROCEDURE acids into protein in muscle and increases incorporation in liver (4). It results in a General. Female rats of the Carworth three- to fourfold increase in liveramino strain were used in two experiments. Rats acid-activating enzymes (5). The nitro- were assigned randomly to dietary treat- gen concentration of liver from protein- ment at 12 to 14 weeks of age, at body deprived rats is reduced and body weight weights averaging approximately 225 and loss is greater than in rats fed an equal 215 g, in experiments 1 and 2, respectively, intake of an adequate diet (6). Informa- Jn each experiment rats were kept in in- tion on changes in body weight and com- dividual wire-bottom cages and offered position of adult animals deprived of pro- water ad libitum from glass water bottles tein is of importance in predicting the attached to the cage, and feed ad libitum effects of such dietary restriction in other from porcelain feed dishes designed for species, including man, and in providing minimum feed wastage. Feed consumption a basis for comparison of the effects of and body weight were recorded every sec- protein deprivation in gravid versus non- Receivedfor publicationJuly 17, 1968.