Malondialdehyde results from lipid peroxidation of polyunsaturated fatty acids. These contain high levels of polyunsaturated fatty acids. All fats are derivatives of fatty acids and glycerol. Fats are constructed from glycerol and fatty acids. Drying oils consist of glycerol triesters of fatty acids. Sardines are a source of omega-3 fatty acids. Triglycerides are synthesized by esterification of fatty acids to glycerol. Most soaps are sodium salts of fatty acids. Most of the fatty acids are unsaturated. Sodium salts of fatty acids are used as soap. In nature, fats are in general triesters derived from glycerol and fatty acids. Foods rich in certain fatty acids may foster a healthy immune system. Cooking oils are composed of various fractions of fatty acids. They can also act as antioxidants for fatty acids. Hydrogenation of unsaturated fatty acids is widely practiced.