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Effect of Amino Acid Imbalance on Nitrogen Retention

I. Effect of a Relative Deficiency of Tryptophan in Dogs^1,2,

Institute of Nutrition of Central America and Panama (INCAP), Guatemala, Central America

The effect of amino acid imbalance on nitrogen retention was studied with young growing dogs, fed a basal diet containing: (in per cent) casein, 8; gelatin, 15; methionine, 0.3; and tryptophan, 0.2. Each diet was fed for three consecutive 4-day balance periods. Omitting one amino acid at a time resulted in a decrease in nitrogen balance with the most marked effect with methionine omission. The variation among the three 4-day periods was considerable when either methionine or tryptophan were omitted from the basal diet — usually because the middle periods gave relatively high nitrogen balance figures. The omission of both amino acids at the same time caused decrease in nitrogen retention over the value obtained with the basal diet. The decrease was, however, less than when only one amino acid was omitted. It was found that the methionine-to-tryptophan ratio of 2.0/1, resulting when the methionine supplement was omitted, and the methionine-to-tryptophan ratio of 6.6/1 when tryptophan was omitted, gave the lowest nitrogen retention figures. Calculation of the methionine-to-tryptophan ratio of various high quality protein foods showed that they contain approximately a 3.4/1 ratio. When the methionine-to-tryptophan ratio was 3.4/1 as in the basal diet or 3.8/1 when both amino acids were omitted, the average nitrogen retention values were higher.

² INCAP Publication I-251.

Manuscript received 22 June 1962.