n-3 polyunsaturated fatty acids (n-3 PUFA) have been postulated to improve the insulin resistance associated with type 2 diabetes since the 1960s when observational studies in the Alaskan Inuit noted a reduced prevalence of type 2 diabetes when this population consumed a traditional diet. These findings were supported by animal studies but results of human intervention studies have been variable with most showing no change in glucose metabolism. More recent studies in growing farm animals suggested that muscle membrane phospholipids required to be enriched to a minimum of 14% n-3 PUFA in order for a change in insulin sensitivity to occur. This study sought to establish the effect of long-term (9 month) high-dose (3g/day) supplement of the n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on insulin sensitivity of glucose and protein metabolism. Thirty-three subjects with impaired glucose regulation underwent hyperinsulinaemic-euglycaemic-euaminoacidaemic clamps pre- and postintervention of n-3 PUFA or a control (maize) oil. A second cohort who all received n-3 PUFA supplementation underwent pre- and post-intervention muscle biopsies. Secondary outcomes included an assessment of inflammatory status and determining whether erythrocyte membrane phospholipid could act as a surrogate for muscle membrane phospholipid. In the clamp cohort, there were no changes in glucose metabolism postintervention; however, there was an increase in insulin-stimulated protein metabolism following the fish oil intervention. In the biopsy cohort, no subject achieved 14% PUFA enrichment in muscle membrane phospholipids; however, all subjects who received n-3 PUFA supplementation did achieve a minimum of 14% enrichment of n-3 PUFA in erythrocyte membrane phospholipid. In agreement with the majority of the literature, n-3 PUFA did not affect glucose metabolism. Insulin-stimulated protein metabolism was improved supporting the findings of another recent human study. These changes in protein metabolism may reduce the sarcopenia associated with aging, potentially delaying the progression of frailty.