We review the international recommendations on oral intake of n-3 fatty acids and their content in the enteral nutrition formulas. Their metabolic actions depend on their metabolization to EPA and DHA. The activity of desaturases catalyzing this process increases with exercise, insulin, estrogens in the fertile women, and peroxisomal proliferators, whereas it decreases with fasting, protein and oligoelements deficiencies, age < 30 years, sedentary lifestyle, cigarette smoking, alcohol, cholesterol, trans and saturated fatty acids, insulin deficiency, and stress hormones (adrenalin and glucocorticoids). Most of the guidelines recommend that 20-35% of the total energy comes from fat, being 7-10% saturated fats, 6-10% polyunsaturated, and 20% monounsaturated, in Spain. The recommendation for n-3 FA is 0.5-2 g/day or 0.5-2% of total caloric intake, with an upper limit of 3 g/day. For n-6 FA, 2.5-10% of total caloric intake, the n-6/n-3 ratio not being well established although most of the guidelines recommend 5:1. The EPA and DHA content should be at least 500 mg per day. Finally, the EPA/DHA ratio is 2:1 in most of them. Standard nutrition formulas present an appropriate fat content, although most of the products containing EPA and DHA exceed the limit of 3 g/day. Among the products with hyperprotein and/or concentrated, only of them contains EPA y DHA. Not all the formulas used for the frail elderly contain EPA or DHA, and in those containing them their concentration may be excessive and with a proportion very dissimilar to that of fish oil.