Insulin resistance and hyperinsulinemia are features of obesity, non-insulin-dependent diabetes mellitus, and other disorders. Skeletal muscle is a major site of insulin action, and insulin sensitivity may be related to the fatty-acid composition of the phospholipids within the muscle membranes involved in the action of insulin.

We determined the relation between the fatty-acid composition of skeletal-muscle phospholipids and insulin sensitivity in two groups of subjects. In one study, we obtained samples of the rectus abdominis muscle from 27 patients undergoing coronary artery surgery; fasting serum insulin levels provided an index of insulin sensitivity. In the second study, a biopsy of the vastus lateralis muscle was performed in 13 normal men, and insulin sensitivity was assessed by euglycemic-clamp studies.

In the patients undergoing surgery, the fasting serum insulin concentration (a measure of insulin resistance) was negatively correlated with the percentage of individual long-chain polyunsaturated fatty acids in the phospholipid fraction of muscle, particularly arachidonic acid (r = -0.63, P<0.001); the total percentage of C20-22 polyunsaturated fatty acids (r = -0.68, P<0.001); the average degree of fatty-acid unsaturation (r = -0.61, P<0.001); and the ratio of the percentage of C20:4 n-6 fatty acids to the percentage of C20:3 n-6 fatty acids (r = -0.55, P<0.01), an index of fatty-acid desaturase activity. In the normal men, insulin sensitivity was positively correlated with the percentage of arachidonic acid in muscle (r = 0.76, P<0.01), the total percentage of C20-22 polyunsaturated fatty acids (r = 0.76, P<0.01), the average degree of fatty-acid unsaturation (r = 0.62, P<0.05), and the ratio of C20:4 n-6 to C20:3 n-6 (rho = 0.78, P = 0.007).

Decreased insulin sensitivity is associated with decreased concentrations of polyunsaturated fatty acids in skeletal-muscle phospholipids, raising the possibility that changes in the fatty-acid composition of muscles modulate the action of insulin.