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Metabolic Patterns in Preadolescent Children

VII. Intake of Niacin and Tryptophan and Excretion of Niacin or Tryptophan Metabolites¹

Human Nutrition Research Division, United States Department of Agriculture, Washington, D. C., Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana, and Georgia Agricultural Experiment Stations, Experiment, Georgia

Three metabolic studies were carried out with a total of 35 normal 7- to 9-year-old girls maintained with controlled diets varying in niacin and tryptophan as well as protein content. Determinations were made for dietary content of niacin and tryptophan.

Urinary excretions were determined for nicotinic acid, N¹-methylnicotinamide (N¹-Me), N¹-methyl-2-pyridone-5-carboxamide (pyridone), quinolinic acid, and tryptophan. Intake was expressed as niacin equivalent (NE) using niacin plus 1/60 tryptophan. Outgo was expressed as niacin metabolites (NM) using the combined excretion of N¹-Me, pyridone, and nicotinic acid, all expressed as nicotinic acid.

The relationship between outgo of NM and intake of NE was positive and linear when average NE intakes varied from 14.5 to 25.4 mg/day, from 6.8 to 12.3 mg/1000 Cal., or from 0.51 to 0.89 mg/kg of body weight.

For the 26 girls using diets without gelatin and average daily NE intakes ranging from 14.5 to 23.2 mg, the average daily NM excreted ranged from 42 to 50% of the intake, with exception of 21% for one girl. For the 9 girls fed diets with added gelatin and average daily NE intakes ranging from 20.3 to 25.4 mg, the average daily NM excreted ranged from 31 to 40% of the intake. The lower excretion of NM for the girls eating the gelatin-containing diets suggests that less tryptophan was converted to niacin. This may have been the result of an amino acid imbalance.

The average ratio of pyridone-to-N¹-Me in the urine decreased from 3.4 to 2.0 as the average dietary NE decreased from 23.2 to 14.5 mg/day.

The excretion of nicotinic acid averaged about 0.2 to 0.3 mg daily. The average excretions of tryptophan ranged from 5 to 9 mg daily, but for one group of 11 girls, excretions decreased when the daily protein intake was reduced from about 0.8 to 0.6 gm/kg of body weight and the tryptophan from 187 to 137 mg. Quinolinic acid tended to be excreted in larger amounts by the girls eating higher protein diets furnishing from 555 to 853 mg of tryptophan daily, and to be depressed for the girls receiving the diet containing an average of 882 mg of tryptophan and 19 gm of gelatin daily.

Manuscript received 4 October 1962.