The Effect of Dietary Fat on Vitamin B12-Methionine Interrelationships

A purified diet containing isolated soybean protein was developed for the study of vitamin B12 in the non-depleted chick. The vitamin B12-sparing effect of methionine in day-old New Hampshire chicks receiving 0, 4 and 24% fat in the diet was determined with the new diet. In confirmation of earlier studies with a crude corn-soybean meal diet, increasing the fat content of the diet increased the severity of the vitamin B12 deficiency that was obtained during 4-week experimental periods. This effect of high dietary fat was lost in the presence of supplemental methionine; however, both vitamin B12 and methionine were necessary for maximum growth. With no fat in the diet, growth depression in the absence of vitamin B12 was very small. In the absence of fat the toxicity of methionine was markedly increased, as indicated by poor growth, poor feather formation, and a moderate incidence of perosis. Some of these changes were less severe in vitamin B12-supplemented chicks. Serum concentrations of total fat, phospholipids, and total cholesterol were not markedly affected by vitamin B12 deficiency, fat level of the diet, or methionine supplementation. Possible roles of vitamin B12 and methionine in fat metabolism and protein synthesis were discussed in relation to these findings.