Plant and animal sources of saturated fat
Current research does not support the widely accepted conclusion that saturated fat causes heart disease. This hypothesis has its roots in research initially published in the 1960s by Ancel Keys, PhD. His Seven Countries Study compared death rates from cardiovascular disease (CVD) to total and saturated fat intake in seven countries and found countries with higher saturated fat consumption had a higher CVD death rate (Sizer & Whitney, 2017, p. 196). However, a 2010 meta-analysis concluded “there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD [coronary heart disease] or CVD.” (Siri-Tarino, Sun, Hu, & Krauss, 2010). Within specific age and gender groups, however, available data was not adequate to determine whether there are CHD or stroke associations with saturated fat (Siri-Tarino et al., 2010). The biological mechanism by which saturated fat causes heart disease never been established. Current research indicates other dietary factors have a greater impact on heart disease risk than saturated fat alone. Lifestyle factors that play a role in CVD include genetics, smoking, obesity, and physical inactivity (Sizer & Whitney, 2017, p. 438).
A 2016 ecological study aimed to identify the main nutritional factors related to CVD in Europe (Grasgruber, Sebera, Hrazdira, Hrebickova, & Cacek, 2016). The study found “a correlation between raised cholesterol in men and the combined consumption of animal fat and animal protein…The most significant dietary correlate of low CVD risk was high total fat and animal protein consumption” (Grasgruber et al., 2016). A “major correlate of high CVD risk,” however, “was the proportion of energy from carbohydrates and alcohol, or from potato and cereal carbohydrates” (Grasgruber et al., 2016). Grasgruber et al. (2016) concluded their “results do not support the association between CVDs and saturated fat…they agree with data accumulated from recent studies that link CVD risk with the high glyceamic index/load of carbohydrate-based diets”.
When discussing cholesterol as it relates to CVD risk, it’s important to distinguish different cholesterol types. HDL is generally considered “good” cholesterol and LDL is considered “bad” cholesterol. There are two sizes of LDL particles: small dense LDL and large bouyant LDL. Small dense LDL is pro-atherogenic, pro-thrombotic, and pro-inflammatory whereas large buoyant LDL may actually be anti-atherogenic (DiNicolantonio, Lucan, & O’Keefe, 2016). Grasgruber et al. (2016) found that although animal fat (especially in combination with animal protein) predicted raised cholesterol levels, “the relationship between raised cholesterol and CVD indicators” in their study was always negative. Lemieux, Lamarche, Couillard C, et al.(2001) concluded variation in the total cholesterol to HDL ratio “may be associated with more substantial alterations in metabolic indices predictive of ischemic heart disease risk and related to the insulin resistance syndrome than variation in the LDL-C/HDL-C ratio”. DiNicolantonio et al. (2016) note “a high concentration of small-dense LDL and a low concentration of large buoyant LDL has been associated with greater CHD risk.” Also important is the triglycerides to HDL ratio (Da Luz, Favarato, Junior, Lemos, & Chagas, 2008). There is data to suggest that dietary saturated fat can decrease small-dense LDL and increase large buoyant LDL; saturated fat may be protective against CHD by shifting the proportion of LDL particles (DiNicolantonio et al., 2016). Additionally, there is not one type of saturated fat. The saturated fatty acid stearate, for example, does not appear to raise LDL levels (DiNicolantonio et al., 2016). Both stearate and laurate (another saturated fatty acid) reduce the total cholesterol/HDL ratio, and thus may actually reduce CHD risk (DiNicolantonio et al., 2016). When dietary saturated fat is replaced with carbohydrates (especially refined carbohydrates such as sugar), total cholesterol tends to increase, HDL tends to fall, and triglycerides tend to rise; these metabolic changes are associated with CHD (DiNicolantonio et al., 2016).
It is important to look at what is included or excluded from the diet when assessing the impact of saturated fat on CHD. All-cause mortality has been found to increase when saturated fat is replaced with trans-fats or omega-6 polyunsaturated oils (DiNicolantonio et al., 2016). Grasgruber et al. (2016) mention an analysis by Mente et al. which found “trans-fatty acids, high glycaemic index/load, and the ‘Western’ diet (including processed and red meat, butter, high-fat dairy products, eggs, and refined cereals) were strongly and consistently related to high CHD risk”. However, the evidence connecting CHD and saturated fat, individual animal products like meat, eggs, and milk, and fat as a whole was weak (Grasgruber et al., 2016). Added sugars (especially fructose and sweeteners containing fructose), refined carbohydrates, trans-fats, and ultra-processed foods are much more likely to result in the metabolic dysfunction that ultimately causes heart disease rather than saturated fat alone.
Works Cited
- Sizer, F. S., & Whitney, E. N. (2017). Nutrition: Concepts and Controversies (14th ed.). Boston, MA: Cengage Learning.
- Siri-Tarino, P. W., Sun, Q., Hu, F. B., & Krauss, R. M. (2010). Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. The American Journal of Clinical Nutrition, 91(3), 535–546. http://doi.org/10.3945/ajcn.2009.27725
- Grasgruber, P., Sebera, M., Hrazdira, E., Hrebickova, S., & Cacek, J. (2016). Food consumption and the actual statistics of cardiovascular diseases: an epidemiological comparison of 42 European countries. Food & Nutrition Research, 60. http://doi.org/10.3402/fnr.v60.31694
- DiNicolantonio, J. J., Lucan, S. C., & O’Keefe, J. H. (2016). The evidence for saturated fat and for sugar related to coronary heart disease. Progress in Cardiovascular Diseases, 58(5), 464–472. http://doi.org/10.1016/j.pcad.2015.11.006
- Lemieux I, Lamarche B, Couillard C, et al. Total Cholesterol/HDL Cholesterol ratio vs LDL Cholesterol/HDL Cholesterol ratio as indices of ischemic heart disease risk in men: The Quebec Cardiovascular Study. Arch Intern Med. 2001;161(22):2685–2692. doi:10.1001/archinte.161.22.2685
- Da Luz, P. L., Favarato, D., Junior, J. R. F.-N., Lemos, P., & Chagas, A. C. P. (2008). High ratio of triglycerides to HDL-Cholesterol predicts extensive coronary disease. Clinics (Sao Paulo, Brazil), 63(4), 427–432. http://doi.org/10.1590/S1807-59322008000400003