Omega-3 fatty acid deficiency and type 2 diabetes mellitus

Initial indications that n-3 PUFA may reduce insulin resistance (IR) came from epidemiological studies showing lower incidence of diabetes in Greenland Inuit's, Alaskan natives and Japanese Islanders compared with their mainland counterparts. Out of the seven longitudinal epidemiological studies conducted subsequently, four reported an inverse association between IR and n-3 PUFA intake, one found no association, and two reported increased IR with increased intake of n-3 PUFA. Homeostatic model of IR (HOMA-IR) was inversely associated with plasma-phospholipids (PL) n-3 PUFA in 4 of 4 studies, erythrocyte n-3 PUFA in 2 of 2 studies, skeletal muscle docosahexaenoic acid (DHA) in 1 study, but it was positively associated with the adipose tissue DHA in 1 study. Out of 23 intervention studies with n-3 PUFA supplementation [fish, fish oils, purified eicosapentaenoic acid (EPA), DHA, α-linolenic acid (ALA) or flaxseed] 11 reported decrease in IR or improved insulin sensitivity, 10 found no change, and two reported increase in IR. These inconsistencies may be due to the relatively high concentrations of n-6 PUFA and low n-3 PUFA with variable amounts of saturated and trans fatty acid in the basal diets, short duration, use of insensitive methods to evaluate IR, or health status of the subjects and interference by their medicines. Despite the inconsistencies, a majority of the studies showed a benefit or no effect and only a few showed adverse effects. Considering that n-3 PUFA reduce the risk for a number of inflammatory chronic diseases, their intake should be increased, and that of n-6 PUFA, saturated and trans fatty acids should be decreased.