INS and Insulin resistance: Subsequently, a study conducted in older adults (age >70) showed a positive relationship between the proportion of palmitic acid (C16:0) in the skeletal muscle phospholipids and the insulin sensitivity index.39 More recently, a small group study confirmed this association and further observed that the fatty acid composition of phosphatidylcholine, and not phosphatidylethanolamine, from skeletal muscle membranes is of particular importance in this relationship.40 In that study, healthy patients were treated with nicotinic acid, an agent known to induce insulin resistance in humans.