Carbohydrate Metabolism in Rats Fed Carbohydrate-free Diets

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Abstract
Young rats were fed a carbohydrate-free diet for 1 week in which fatty acids provided 82% and protein (casein), 18% of the calories (diet FA). This diet contained limiting amounts of glucose precursors. In the diets of other groups of rats, glucose (4% of the calories) or neutral fat (82% of the calories) were incorporated in place of isocaloric amounts of fatty acids. A high carbohydrate diet and laboratory ration served as controls. With all experimental diets increased gluconeogenesis and decreased glucose utilization were observed. Activities of glucose-6-phosphatase, fructose-1,6-diphosphatase and glutamic-pyruvic transaminase (GPT) in the liver were enhanced and glucokinase activity and glucose tolerance decreased. All these effects disappeared after 1 week of feeding laboratory ration. Only GPT activity remained slightly increased. Most marked changes were observed when diet FA was fed: growth, glucose tolerance, liver GPT activity and serum corticosteroids were more affected than in rats on diets containing neutral fat or supplemented with glucose. It appears that certain minimal amounts of carbohydrates (or their precursors) are necessary to prevent these effects of severe restriction of dietary carbohydrates.