Dietary fats vary in their proportion of saturated and unsaturated fatty acids. They also vary in the specific fatty acids they contain, which further determines their biological effects in the body. The general categories of fatty acids are:
- Saturated fatty acids, found mostly in animal products such as meat, milk, and butter, as well as in tropical oils and chocolate.
- Monounsaturated fatty acids, as in olive and canola oils, avocados, and nuts.
- Omega-6 polyunsaturated fatty acids, predominating in many vegetable oils.
- Omega-3 polyunsaturated fatty acids, as in fish and some plant foods (such as walnuts, flaxseed, and canola oil). Fish rich in these fats have been linked to reduced cardiovascular risk.
- Trans fatty acids, produced when liquid fats are partially hydrogenated to make them more solid. These raise LDL, lower HDL (“good”) cholesterol, and have other harmful effects. They are being phased out of foods.
Keep in mind that the fats in all foods contain both saturated and unsaturated fatty acids. Thus, up to one-quarter of the fat in fish is saturated, for instance, and nearly half the fat in meat is actually monounsaturated.