Effect of Source of Carbohydrate as Influenced by Dietary Fat: Carbohydrate ratio and forced exercise in rats

Abstract

The effects were studied of changing the carbohydrate source in diets high or low in fat and fed to sedentary or force-exercised rats. Eighty mature, male rats were either force-exercised by treadmill-running every day or allowed voluntary activity in an activity cage. The 40 animals receiving each exercise treatment were then fed ad libitum either a high fat-low carbohydrate diet or a diet low in fat and high in carbohydrate. Equicaloric intakes of the 2 diets provided equal intakes of protein, vitamins and minerals. The 20 animals receiving each diet at each exercise level were divided into 4 groups of 5 animals each to receive their dietary carbohydrate as: 1) cornstarch, 2) lactose, 3) sucrose, or 4) a mixture approximating the carbohydrate composition of an average U. S. “market basket” diet. The animals fed lactose as the only carbohydrate in a low fat-high carbohydrate diet had diarrhea and weighed less than all other animals, even when diets were corrected to equicaloric intakes by analysis of covariance. Metabolism of 1-14C- and 6-14C-glucose to 14CO2 and U-14C-glucose to citrate-14C indicated greater activity of the HMP shunt pathway in animals fed lactose. The moderate level of forced exercise used in this study significantly lowered the ingesta-free body weights of animals fed equicaloric amounts of the high fat-low carbohydrate diets, but had no effect on the body weights of animals fed equicaloric amounts of the high carbohydrate-low fat diets. This appeared to indicate a greater muscular efficiency in rats fed the high carbohydrate-low fat diets than in those fed the high fat-low carbohydrate diets. Body composition was altered by all three of the main experimental variables. Animals fed the high fat-low carbohydrate diet had more body fat than animals of the same weight fed the high carbohydrate-low fat diet. Force-exercised animals had less body fat than animals of the same weight allowed voluntary activity only. Among rats of the same weight, those fed starch as the only source of carbohydrate had more body fat than those fed the other carbohydrate sources. However, rats fed starch had a lower carcass concentration of cholesterol than rats fed the other carbohydrate sources. Rats fed the mixture of carbohydrates at either a high or a low level in the diet increased in body cholesterol more rapidly as they gained weight than rats fed the single carbohydrate sources. Weight control was of primary value in limiting the cholesterol content of the animals fed the carbohydrate mixture, regardless of fat:carbohydrate ratio of the diet.