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Effect of Amino Acid Imbalance in Rats Fed Ad Libitum, Interval-fed, or Force-fed¹

Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

Since food intake has been shown to be of utmost importance in the response of animals fed amino acid imbalanced diets, a study was made in which rats were fed once a day or were force-fed and the food intake and growth were followed and compared with ad libitum-fed rats. Amino acid imbalances were created by adding 2 to 12% of amino acid mixture lacking one indispensable amino acid to low protein diets. The severity of the adverse effect on food intake and growth increased with increasing concentration of the imbalancing amino acid mixture added to the diet. Supplementation of the imbalanced diets with the limiting amino acid (0.45% of DL-threonine) completely prevented the adverse effects caused by the addition of 5.4% of an amino acid mixture lacking threonine to a 6% casein diet. The food intake and growth of interval-fed rats (trained to eat a single 2-hour meal daily) fed the imbalanced diet was not depressed until the concentration of the imbalancing amino acid mixture was greatly increased. Force-feeding stimulated growth of rats receiving different imbalanced diets without causing obvious abnormalities.

² Present address: Department of Physiological Sciences, School of Veterinary Medicine, University of California, Davis, California 95616.

³ Present Address: Biochemistry Department, University of Wisconsin, Madison, Wisconsin.

Manuscript received 22 February 1968.