What Impact Do Cholesterol and Saturated Fat Have on Heart Disease?

Heart disease accounts for about 25 percent of all deaths in the United States, with almost 600,000 Americans dying from it each year.1 It has been among the top five leading causes of death in the United States since 1935.2 From the time the first set of dietary goals for Americans was issued in 1977, reducing intake of dietary cholesterol and saturated fat has been advised because they were thought to increase risk of developing and dying from heart disease.3 As a result, nutrition recommendations have advised a higher carbohydrate, lower fat and lower cholesterol diet. 

However, since heart disease remains one of the leading causes of death today, and incidence of other chronic diseases has increased, several questions arise. Does dietary cholesterol and saturated fat intake really have an impact on cardiovascular disease? Are people doing themselves more harm than good by eating a higher carbohydrate diet just to decrease intake of cholesterol and saturated fat?

Both cholesterol and fatty acids (including saturated fat) perform functions in the human body. Cholesterol synthesizes cell membranes, steroid hormones (including vitamin D) and bile acids. In most people, production by the liver and absorption of cholesterol will automatically adjust based on what is available in the diet and needed by the body to maintain homeostasis.4 Fatty acids are a major part of the phospholipid component of cell membranes, are needed to transport and absorb fat-soluble vitamins, and are used as a fuel source.

It has been accepted that high intakes of cholesterol and saturated fats raise total cholesterol and LDL-cholesterol levels, which increased risk (or even caused) cardiovascular disease. However, only about 25 percent of people experience a significant rise in plasma cholesterol levels (both LDL and HDL) after consuming foods high in cholesterol, such as eggs.5,6,7 In addition, several large epidemiologic studies, including the Framingham Heart Study, the Lipid Research Clinics Study, the Health Professionals Study, and the Nurses’ Health Study found no significant association between dietary cholesterol intake and cardiovascular disease risk or death.5 Additionally, a meta-analysis of 21 prospective epidemiologic studies showed no significant association between saturated fat intake and increased risk of cardiovascular disease.8

It has been suggested that there are more useful indicators in evaluating cardiovascular risk. Rather than total and LDL cholesterol, the LDL/HDL ratio — which does not seem to be negatively impacted by dietary cholesterol and saturated fat intake — may be a better marker.5 Another marker that has been studied for years but is not widely discussed is LDL particle size. Smaller, denser LDL particles are more atherogenic — tend to promote the formation of fatty plaques in the arteries — than larger LDL particles.7,9,10 They appear to correspond with intake of dietary carbohydrates, particularly simple sugars and high glycemic starches,11 and are associated with high triglyceride levels, low HDL-cholesterol levels and abdominal fat,9 all of which are risk factors for metabolic syndrome. 

Recent research that analyzed studies from 1957 to 2013 also found that simply lowering dietary fat and cholesterol is not likely to provide the most benefit in reducing risk for cardiovascular disease.12 Emphasis on higher quality diets — including less processed whole foods rather than focusing on one element such as limiting fat, cholesterol, calories or portions — will likely produce more long-term health benefits and reduce risk for other chronic diseases as well.

References
1. Centers for Disease Control and Prevention. Genomics and Health: Heart Disease and Family History. Accessed 02/06/14. 
2. Hoyert, D. (2012). 75 Years of Mortality in the United States, 1935-2010. NCHS Data Brief, No. 88. Accessed 02/06/14.
3. Truswell, A. (1987). Evolution of dietary recommendations, goals, and guidelines. American Journal of Clinical Nutrition, 45: 1060-72.
4. Lecerf, J-M. and M. deLorgeril (2011). Dietary cholesterol: from physiology to cardiovascular risk. British Journal of Nutrition, 106: 6-14. Accessed 01/29/14.
5. Djousse, L. and J. M. Gaziano. (2009). Dietary cholesterol and coronary artery disease: a systematic review. Current Atherosclerosis Reports, 11: 418-422.
6. Fernandez, M. (2010). Effects of eggs on plasma lipoproteins in healthy populations. Food Funct. 1 (2): 156-60. Accessed 02/09/14.
7. Barona, J.  and M. L. Fernandez (2012). Dietary cholesterol affects plasma lipid levels, the intravascular processing of lipoproteins and reverse cholesterol transport without increasing the risk for heart disease. Nutrients, 4: 1015-1025. Accessed 02/08/14.
8. Siri-Tarino, PW et al. (2010). Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. American Journal of Clinical Nutrition, 91: 1535-1546. Accessed 02/06/14.
9. Arsenault, B. et al (2007). Cholesterol levels in small LDL particles predict the risk of coronary heart disease in the EPIC-Norfolk prospective population study. European Heart Journal, 28: 2770-2777. Accessed 02/07/14.
10. Krauss, RM. (2001). Dietary and genetic effects on low-density lipoprotein heterogeneity. Annual Review of Nutrition, 21: 283-95.
11. Siri, PW and RM Krauss (2005). Influence of dietary carbohydrate and fat on LDL and HDL particle distributions. Current Atheroscerosis Reports, 7 (6): 455-459. Accessed 02/09/14.
12. Dalen, JE and S Devries (2014). Diets to prevent coronary heart disease 1957 to 2013: What have we learned? The American Journal of Medicine, in press. Accessed 02/10/14.

Michelle Baglio
Michelle Baglio, RD, LD, is a clinical dietitian at ‎CHI Franciscan Health in Seattle.