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Nutritional Studies with the Guinea Pig

VII. Niacin

National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, Bethesda, Maryland

The young guinea pig requires a dietary source of niacin unless there is an ample supply of available tryptophan. Like other animals, it has the capacity to produce niacin from tryptophan.

The dietary requirement for niacin is affected by the amount and type of protein in the diet, particularly with respect to its tryptophan content. Maximal growth was obtained with a purified diet by the addition of 1 mg of niacin per 100 gm, either to a 30% casein diet or to one containing 20% of casein supplemented with 1% of L-arginine. With a diet containing 30% of purified soybean protein, maximal growth was obtained without addition of niacin, but with a 20% level of this protein supplemented with 0.5% of DL-methionine, more than 1 mg of niacin, possibly as much as 2 mg, was necessary. With a diet containing 10% of the soybean protein and 10% of gelatin, supplemented with the essential amino acids except tryptophan and arginine, the niacin requirement was found to be 2.5 mg per 100 gm. With this latter diet, maximal growth was not obtained without addition of tryptophan.

The conversion of tryptophan to niacin appears to occur more efficiently with the soybean protein than with casein.

Extremely high levels of niacin were somewhat toxic to the guinea pig when fed the gelatin-containing diet if the amount of available tryptophan was insufficint to supply the need for tryptophan as such.