The Effect of Diet on Cardiovascular Disease and Lipid and Lipoprotein Levels

The role of lipids and lipoproteins as causal factors for cardiovascular disease (CVD) is well established. Dietary saturated fatty acids (SFA), which are in milk, butter, cheese, beef, lamb, pork, poultry, palm oil, and coconut oil increase LDL-C and HDL-C. The increase in LDL-C is due to a decrease in hepatic LDL clearance and an increase in LDL production secondary to a decrease in hepatic LDL receptors. Monounsaturated fatty acids (MUFA) are in olive, canola, peanut, safflower, and sesame oil, and avocados, peanut butter, and many nuts and seeds and polyunsaturated fatty acids (PUFA) are in soybean, corn, and sunflower oil, and some nuts and seeds, tofu, and soybeans. Both MUFA and PUFA lower LDL-C by increasing hepatic LDL receptor activity. Dietary cholesterol is found in egg yolks, shrimp, beef, pork, poultry, cheese, and butter and increase LDL-C but the effect is modest and varies with approximately 15-25% of individuals being hyper-responders with more robust increases. Dietary cholesterol reduces hepatic LDL receptor activity, decreasing the clearance and increasing the production of LDL. Trans fatty acids (TFA) occur naturally in meat and dairy products and are formed during the partial hydrogenation of vegetable fat. TFA increase LDL-C and decrease HDL-C. Carbohydrates (CHO) can be divided into high-quality, for example fruits, legumes, vegetables, and whole grains, or low-quality, which include refined grains, starches, and added sugars. CHO increase TG with low quality CHO, particularly added sugars, having a more robust effect. Dietary CHO, particularly fructose, promotes hepatic de novo fatty acid synthesis leading to increased VLDL secretion. Fiber is found mostly in fruits, vegetables, whole and unrefined grains, nuts, seeds, beans, and legumes and phytosterols are naturally occurring constituents of plants and are found in vegetable oils, cereals, nuts, fruit and vegetables. Both dietary fiber and phytosterols decrease LDL-C by decreasing intestinal cholesterol absorption. With regards to CVD there are very few well conducted randomized controlled trials and most of the information is derived from observational studies that demonstrate associations. These observational studies have found that fruits, vegetables, beans/legumes, nuts/seeds, whole grains, fish, yogurt, fiber, seafood omega-3 fatty acids, and polyunsaturated fats were associated with a decreased risk of CVD while unprocessed red meats, processed meats, sugar-sweetened beverages, high glycemic load CHO, and trans-fats were associated with an increased risk of CVD. Randomized trials have shown that a Mediterranean diet reduces CVD. Based on this information current guidelines for the general population recommend 1. A diet emphasizing intake of vegetables, fruits, legumes, nuts, whole grains, and fish 2. Replacement of SFA with MUFA and PUFA 3. A reduced amount of dietary cholesterol 4. Minimizing intake of processed meats, refined CHO, and sweetened beverages and 5. Avoidance of TFA. For individuals with a high LDL-C limiting dietary SFA, TFA, and cholesterol and increasing fiber and phytosterols will help lower LDL-C while in individuals with high TG limiting low quality CHO, particularly simple sugars, and ethanol with weight loss, if indicated, will help lower TG. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.