Saturated Fat: Friend or Foe?

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Saturated fat has long been demonized by public health experts due to its established effect on raising cholesterol and, by proxy, association with increased cardiovascular disease. However, a recent editorial by Malhotra et al. (2016) [1], claiming that reduced saturated fat has no effect on coronary heart disease, has caught the attention of the media and the public, many of whom are now wondering if they can consume all of the butter and bacon they want without worrying about the health of their hearts.

To understand the complex relationship between dietary fat and health, it is important to distinguish between the two primary types of dietary fat. Unsaturated fats are found in a variety of plant-based oils (olive, canola, avocado, etc.) and fatty fish, and have been established as protective factors in heart health for many years due to their ability to raise HDL (the “good” cholesterol) and decrease LDL (the “bad” cholesterol). Saturated fats, on the other hand, are found in fatty meats, lard, full fat dairy products, coconut, and dark chocolate, and have been historically associated with heart disease because of their known effect on increasing total cholesterol, including both LDL and HDL. (The third type of fat, trans fat, has a long established association with inflammation and cardiovascular disease markers, and will not be discussed here).

So what does the research say? It turns out that the scientific community is just as confused as we are. Some meta-analyses and systematic reviews have found no association between saturated fat and heart disease [2,3]. Similarly, the Women’s Health Initiative (a large, randomized controlled trial with over 45,000 women) found no significant difference in heart disease and total mortality between women consuming a diet low in saturated fat versus a traditional diet [4,5,6]. These findings may be partially due to the existence of different types of LDL: saturated fat has been shown to change LDL composition from small, dense particles (associated with plaque formation and heart disease) to larger particles that have no effect on the heart due to their inability to penetrate the arterial wall [7-10].

However, bacon lovers should not rejoice just yet. The “diet-heart hypothesis” [11,12] has provided the basis for recommendations from the National Institutes of Health’s Cholesterol Education Program and Health Canada for many years. It predicts that because saturated fat is known to increase cholesterol and high cholesterol is associated with heart disease, replacing saturated fat with unsaturated fat reduces the risk of cardiovascular disease.

Following the pro-saturated fat editorial from Maholtra et al. in 2016 [1], many public health and nutrition experts spoke out against the paper and its conclusions due to its somewhat biased assessment and lack of scientific rigour [13]. For example, some high quality research papers, such as the Cochrane review that showed a 17% reduction in cardiovascular disease in individuals following a diet low in saturated fat [14], were not included in the paper’s findings. Another important consideration is the replacement energy source when saturated fat is reduced in the diet. Studies show that when saturated fat is replaced with refined carbohydrates and sugars, rates of heart disease and related mortality remain unchanged. However, when saturated fat is replaced with unsaturated fat, rates of cardiovascular disease decrease, leading authors to suggest that increasing unsaturated fat intake is more likely to improve heart health than reducing saturated fat intake [13].

The research on saturated fat and heart health is evidently conflicting. What we do know, however, is that all of the dietary patterns with strongly established positive health outcomes (i.e. the Mediterranean [15] and DASH [16] diets) are low in saturated fat. Although, this doesn’t necessarily mean that foods high in saturated fat cause heart disease. The Mediterranean and DASH diets, for example, are also low in refined sugars and carbohydrates and high in fruits, vegetables, legumes, and fish. This points to the notion that perhaps we should be moving away from vilifying some macronutrients and putting others on pedestals, and instead, focusing on overall dietary patterns and lifestyle habits that are proven contributors to health and wellness.

 

References

1. Malhotra, A., Redberg, R.F., Meier, P. (2016). Saturated fat does not clog the arteries : coronary heart disease is a chronic inflammatory condition, the risk of which can be effectively reduced from healthy lifestyle interventions. British Journal of Sports Medicine Published Online First: 25 April 2017. doi: 10.1136/bjsports-2016-097285

2. 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. American Journal of Clinical Nutrition, 91(3), 535-546. doi: 10.3945/ajcn.2009.27725

3. Chowdhury, R., Warnakula, S., Kunutso, S., Crowe, F., Ward, H.A. et al. (2014). Association of dietary, circulating and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Annals of Internal Medicine, 160(6), 398-406.

4. Women’s Health Initiative. Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute. Retrieved from https://www.nhlbi.nih.gov/whi/background.htm

5. Howard, B.V., Van Horn, L., Hsia, J., Manson, J.E., Stefanick, M.L. et al. (2006). Low-fat dietary pattern and risk of cardiovascular disease: the Women’s Health Initiative randomized controlled dietary modification trial. Journal of the American Medical Association, 298(6), 655-666. doi: 10.1001/jama.295.6.655

6. Howard, B.V., Manson, J.E., Stefanick, M.L., Beresford, S.A., Frank, G. et al. (2006). Low fat dietary pattern and weight change over 7 years: the Women’s Health Initiative dietary modification trial. Journal of the American Medical Association, 295(1): 39-49. doi: 10.1001/jama.295.1.39

7. Krauss, R.M. (1994). Heterogeneity of plasma low-density lipoproteins and atherosclerosis risk. Current Opinions in Lipidology, 5(5), 339-49. doi: 10.1097/00041433-199410000-00005

8. Camps, H., Genest J.J., Blijlevens, McNamara, J.R., Jenner, J.L. et al. (1992). Low density lipoprotein particle size and coronary artery disease. Arteriosclerosis, Thrombosis, and Vascular Biology, 12, 187-195. https://doi.org/10.1161/01.ATV.12.2.187

9. Packard, C., Caslake, M., Shepherd, J. (2000). The role of small, dense low density lipoprotein (LDL): a new look. International Journal of Cardiology, 74(1), S17-S22. https://doi.org/10.1016/S0167-5273(99)00107-2

10. Siri-Tarino, P.W., Sun, Qi., Hu, F.B., Krauss, R.M. (2010). Saturated fat, carbohydrate, and cardiovascular disease. American Journal of Clinical Nutrition, 91(3), 502-509. doi: 10.3945/acjn.2008.26285

11. Sherwin, R. (1978). Controlled trials of the diet-heart hypothesis: some comments on the experimental unit. American Journal of Epidemiology, 108, 92-99.

12. American Heart Association: National Diet-Heart Study Research Group Executive Committee on Diet and Heart Disease (1969). The national diet heart study final report. American Heart Journal, 77(4), 574.

13. Practice-Based Evidence in Nutrition. Benefits of Reducing Saturated Fat Intake Criticized. Retrieved from http://www.pennutrition.com/TrendingTopics.aspx

14. Hooper, L., Martin, N., Abdelhamid, A., Smith, D. (2015). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Systematic Review, 10(6). doi: 10.1002/14651858.CD011737

15. Mente, A., de Koning, L., Shannon, H.S., Anand, S.S. (2009). A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease. Archives of Internal Medicine, 169(7): 659-69. doi: 10.1001/archinternmed.2009.38

16. Vollmer, W.M., Sacks, F.M., Ard, J., Simons-Morton, D.G., Conlin, P.R. et al. (2001). Effects of diet and sodium intake on blood pressure: subgroup analysis of the DASH-sodium trial. Annals of Internal Medicine,135(12), 1019-1028. doi: 10.7326/0003-4819-135-12-200112180-00005

 

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