Alpha-linolenic acid deficiency in patients on long-term gastric-tube feeding: estimation of linolenic acid and long-chain unsaturated n-3 fatty acid requirement in man.

Alpha-linolenic acid deficiency is described in four adults fed by gastric tube. In plasma and erythrocytes, total lipid 20:3n-9 was slightly increased but total n-6 fatty acids, arachidonic acid, and dihomo-gamma-linolenic acid were normal. Total n-3 fatty acids, 18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3 were decreased in both plasma and erythrocytes. Patients had a slight but definite scaly dermatitis, which disappeared with essential fatty acids supplementation. Simultaneously, levels of 18:3n-3, 20:5n-3, 22:5n-3, 22:6n-3, 20:3n-9, and total n-3 fatty acids became normal while 18:2n-6, 20:3n-6, 20:4n-6, and total n-6 acids were unchanged or slightly lowered. Estimated minimal daily requirement of linolenic acid and of long-chain unsaturated n-3 acids in adults is approximately 0.2-0.3% and 0.1-0.2%, respectively, of total energy intake. Results suggest that conversion of linolenic acid to 22:6n-3 is increased in linolenic acid deficiency.