Free fatty acids (FFA) are fatty acid molecules circulating in the blood unattached to glycerol or other carriers — that is, not bound up as triglycerides, phospholipids, or cholesterol esters. Released from adipose tissue by the action of hormone-sensitive lipase, they are a major fuel for muscle, heart, and liver, especially during fasting and prolonged exercise when glucose runs low. Chronically elevated FFA levels are linked to insulin resistance and type 2 diabetes, since excess fatty acids interfere with glucose uptake in muscle. In food chemistry the same term describes fatty acids liberated from triglycerides by lipase activity or hydrolysis — a key measure of fat breakdown in dairy products, frying oils, and stored foods, where rising FFA signals rancidity.