Dietary Fat: The Good, the Bad, and What Is Best?

Dietary fat is a macronutrient comprised of many different lipids and fatty acids some of which are essential nutrients. The fatty acid classes are saturated (SFA), monounsaturated (MUFA), polyunsaturated (PUFA) (omega-6 and omega-3 fatty acids), and trans (TFA). Unsaturated fatty acids typically exist in the cis configuration and differ structurally based on chain length and the number of carbon-to-carbon double bonds. Unsaturated fatty acids also exist in trans isomer configurations, which occur as the result of partial hydrogenation (via industrial synthesis or by naturally occurring biohydrogenation in ruminant animals). The different fatty acid classes have varying effects on lipids and lipoproteins that affect risk of cardiovascular disease (CVD). All TFA increase CVD risk, and, as a result, industrially produced TFA have been banned in the US food supply. SFA increase low-density lipoprotein-cholesterol (LDL-C) and increase CVD risk. Replacement of SFA with unsaturated fatty acids or carbohydrates (preferably whole grains) reduces LDL-C and CVD risk. Dietary guidelines recommend a healthy dietary pattern with <10% total calories from SFA, which should be achieved by replacing SFA with unsaturated fat or carbohydrate from whole grains. The fat content of the diet will vary based on the replacement macronutrient for SFA.