Some Physiological Relationships of Protein, Fat, Choline, Methionine, Cystine, Nicotinic Acid and Tryptophane

The primary deficiency in diets containing 18% or less of casein was found to be labile-methyl groups unless supplementary choline or methionine was added. The deficiency of labile methyl was aggravated by the addition of cystine or cystine and fat. Supplementary methionine as the free amino acid was more effective than methionine combined in the casein molecule. The second demonstrable deficiency in low-fat diets containing 18% or less of casein was nicotinic acid. Tryptophane or a high level of casein (25%) counteracted the deficiency of nicotinic acid. A high level of fat (30%) tended to counteract the deficiency of nicotinic acid. This was probably a nicotinic acidsparing effect as the energy metabolism shifted from carbohydrate to fat and indicates that nicotinic acid, like thiamine, functions primarily in carbohydrate metabolism. Only when the deficiencies of labile methyl and nicotinic acid were remedied, was a deficiency of cystine (or sulfur amino acid) demonstrable. Methionine corrected both the labile methyl and the sulfur amino-acid deficiencies. The possible nutritional significance of the findings is discussed.