THE FATTY ACIDS OF HUMAN MILK. II. ALTERATIONS PRODUCED BY MANIPULATION OF CALORIC BALANCE AND EXCHANGE OF DIETARY FATS*†

This report describes specific alteration of the fatty acid pattern of human milk produced by rigidly controlled variations in the maternal diet. The subject was a 23-year old white para 3 who had a normal pregnancy and delivered spontaneously at term. The baby girl was breastfed exclusively 6 feedings/day at 4-hour intervals. An orally administered liquid formula supplemented by vitamins and minerals was the sole nourishment of the mother. Maternal milk output was determined by weighing the baby immediately before and after each nursing. Milk samples were collected at the end of each dietary period for chemical analysis. 2 independent but complementary methods the gas liquid chromatography and ultraviolet spectrophotometry after isomerization with alkali were used to analyze fatty acid patterns. The experimental design consisted of: promoting of synthesis of milk fat from carbohydrates by feeding excess calories and no fat (period 3); promotion of transfer of depot fat by feeding deficient calories (period 4); and promotion of transfer of dietary fat by feeding excess calories as corn oil (period 5). The effects of substituting 1 fat for another were compared in periods 2 (lard) and 7 (corn oil). The results show that the fatty acid composition of human milk can be radically altered without affecting milk volume or milk fat output. During energy equilibrium milk fat appears like dietary fat. During caloric deficiency milk fat resembles human depot fat. These findings show that fatty acid pattern of human breast milk is influenced by transfer of dietary or depot fat. During excess nonfat calories the milk exhibited a striking increase in lauric and myristic acids and a marked decline of all polyenoic acid. None of the serum ester groups (cholesterol esters triglycerides and phospholipids) showed a parallel rise in these acids. The study also shows that human mammary acid synthesis differs in many ways from that in extramammary depots.