AHA, Dietary Guidelines Advise Reducing CVD Risk with Unsaturated Dietary Fats

By Christine Werner, PhD, RD, PA-C

A recently published presidential advisory from the American Heart Association (AHA) concludes that replacing saturated fat and refined carbohydrates with unsaturated fats reduces low-density lipoprotein cholesterol (LDL-C) and risk of cardiovascular disease (CVD) in both men and women.¹

No single dietary fat contains 100% of any given fatty acid; rather, they contain a varied concentration of many fatty acids. Sources of predominantly saturated fat include animal products such as dairy, butter, lard and tallow, as well as plant sources like palm and coconut oil. Rich sources of unsaturated fats composed of polyunsaturated fats (PUFA) and monounsaturated fats (MUFA) include vegetable oils such as soybean, canola, corn, safflower, and sunflower oils. Soybean oil is a particularly rich source of dietary unsaturated fat because it has a high percentage of PUFA and is the most widely consumed vegetable oil in the American diet.² Additional dietary sources of PUFA and MUFA include avocados and tree nuts like almonds, pistachios, pecans, hazelnuts and cashews. 

The Dietary Guidelines for Americans recommend consumption of less than 10% of calories from saturated fats.³ While research tends to support this recommendation, at least one study found that replacing saturated fat with an equal number of calories from carbohydrates failed to show CVD risk reduction unless the carbohydrates were in the form of whole grains.⁴

The AHA presidential advisory included a meta-analysis of four randomized clinical trials (RCTs) that evaluated the effects of replacing saturated fat with PUFA on cardiovascular events rather than just risk factors such as blood lipids.¹ Results from the meta-analysis revealed a 29% reduction in CVD events when saturated fat was replaced with polyunsaturated fat for at least two years.¹ Of note, 3 of the 4 RCTs described their primary source of PUFA as soybean oil, while the fourth trial lacked information on dietary fat sources. 

Additional meta-analyses and systematic reviews evaluating the data of select RCTs specifically investigating the replacement of saturated fat with PUFA on CVD risk reveal an overall significant CVD risk reduction of 19%⁵ and 27%,⁶ respectively.

While all commonly used vegetable oils on the market today contain varying degrees of saturated, MUFA and PUFA, there is somewhat more evidence to support the replacement of saturated fat with PUFA, compared to MUFA-predominant oils.^2,7 This conclusion is due to the fact that long-term RCTs have shown that replacement of saturated fat with PUFA sources decreases the clinical incidence of CVD while no such studies have been conducted with MUFA sources. The available data for MUFA-predominant oils are based on CVD risk factors rather than clinical endpoints.

Both linoleic (omega-6) and alpha-linolenic acid (omega-3) are essential fatty acids. Alpha-linolenic acid occurs naturally in soybean and canola oil, although soybean oil is the main source of this fatty acid in the American diet because of its widespread use.⁸ Physiologically, the essential fatty acids help regulate the immune system and blood pressure and are involved in brain development. 

Oleic acid is an omega-9 MUFA found abundantly in various animal fats and vegetable oils. Because oils high in PUFA are susceptible to oxidation and therefore have a reduced shelf and fry life, high oleic vegetable oils were introduced in the market in 2011.⁸ Clinical trials have shown that replacement of saturated fat with high oleic oils including soybean and canola oils favorably alters blood lipids. In a systematic review analyzing clinical trials that replaced saturated fat with high-oleic soybean oil for at least three weeks, total cholesterol decreased by 8%, LDL cholesterol by 10.9%, and apolipoprotein by 7.9%.⁹ 

While recent marketing efforts have promoted the intake of coconut oil to improve HDL cholesterol status, coconut oil is approximately 82% saturated fat, which would be expected to raise LDL cholesterol and could outweigh any CVD risk reduction benefit. The AHA and the Dietary Guidelines do not recommend the intake of coconut oil as part of a heart healthy diet.^1,3

In summary, there is consistent clinical evidence that lowering saturated fat intake and replacing this energy source with PUFA and/or MUFA lowers the risk of CVD. Vegetable oils and vegetable blend oils generally contain fewer than 4 grams of saturated fat per tablespoon. ^2,7

References

1. Sacks FM, Lichtenstein AH, Wu JHY, at al.  Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association.  Circulation. 2017;Sept 5;136(10):e1-e24. 

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2. https://health.gov/dietaryguidelines/2015/guidelines/
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7. Baer D. High Oleic Soybean Oil Improves Lipid Levels.SoyConnection.2017:25(4):3-4.
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