Soybean Oil: An Underappreciated Source of Nutrition

Discussions about soy nutrition often focus on protein, which is not surprising since protein-rich diets are popular, and soybeans are among the best plant sources of this nutrient.^1-3 But the fat in soybeans actually plays a bigger role in U.S. diets. Soy oil accounts for approximately 7% of the total calorie intake of Americans.⁴

The importance of soy oil in diets may escape many Americans since it’s usually marketed as vegetable oil. The health attributes of this oil often go unappreciated, too. Soybean oil is a good choice for those looking to choose more healthful fats. It’s high in health-promoting polyunsaturated fat (PUFA) with a moderate amount of monounsaturated fat.⁵ Replacing saturated fat in meals with PUFA lowers LDL-cholesterol levels and is associated with reduced risk of coronary heart disease (CHD). Soybean oil provides over 40% of our intake of both essential fatty acids.⁴  One of these is the omega-3 fatty acid alpha-linolenic acid (ALA), an essential nutrient that can fall short in plant-based diets.

The first study showing that soybean oil lowers blood cholesterol levels in humans was published 30 years ago.⁶  Since then, several more studies confirmed these initial findings.  The cholesterol-lowering effect of soybean oil was formally recognized in 2017, when the U.S. Food and Drug Administration (FDA) approved a health claim for soybean oil and CHD. The suggested language for this claim reads “Supportive but not conclusive scientific evidence suggests that eating about 1½ tablespoons (20.5 grams) daily of soybean oil, which contains unsaturated fat, may reduce the risk of coronary heart disease.”⁷

Although corn, canola, and olive oils have received similar claims, the FDA has suggested more cautious language regarding their benefits, noting that the evidence is limited or, in the case of corn oil, “very limited.”

Questions about the healthfulness of soybean oil have focused on misunderstandings about effects of omega-6 fats, which make up much of the fat in soybeans. In the past, high omega-6 fatty acid intake was thought to promote inflammation, a condition that is involved in the etiology of many chronic diseases, including cancer and CHD. In particular, a high ratio of omega-6 fat to omega-3 fat was thought to drive inflammation. There is no biological basis for this concern, however, as numerous studies have shown that soybean oil does not increase inflammation. The World Health Organization,⁸ the American Heart Association,⁹ and the European Food Safety Authority,¹⁰ among other leading health organizations have concluded that the ratio of these two fats does not predict disease risk.

In fact, consuming too little omega-6 fat is thought to account for about 10% of global CHD mortality.¹¹ Furthermore, in 80% of nations it was estimated that at least twice as many CHD deaths were due to inadequate intake of omega-6 PUFAs than to excessive intake of saturated fat.¹¹ Getting enough of both the omega-6 and omega-3 fats is one key that may prevent heart disease.

A recently published paper in the journal Nutrition clarified the issues around fats and inflammation and also around the relationship of omega-6 fats to oxidative stress.¹² Like inflammation, oxidative stress is involved in the etiology of many diseases.  While oils high in PUFA may be  more prone to oxidation, two of three studies cited in a recent review found soybean oil did not increase oxidation..¹² Furthermore, the impact of PUFAs in reducing LDL-cholesterol outweighs any potential effects of oxidation.  By the way, omega-6 fat was also recently found to be associated with a decreased risk of developing diabetes.¹³

Questions have also been raised about the effects of omega-6 fats on the production of the long chain omega-3 fats DHA and EPA. These are the fats that are found in fish oils. They can also be produced from the essential omega-3 fat ALA which is found in some nuts, seeds, and oils, including soybean oil. However, omega-6 fats inhibit this process. But most evidence suggests that conversion of ALA to DHA and EPA is inefficient regardless of the amount of omega-6 fat in the diet. According to the American Heart Association, any potential disadvantage regarding production of DHA and EPA is outweighed by the coronary benefits of omega-6 PUFA.⁹

In addition to its health benefits, soybean oil has a number of culinary attributes. Its neutral flavor means it can be used in a variety of savory and sweet dishes and will not overpower  flavors in a recipe. It also has a high smoke point, making it a good choice for higher-temperature cooking. Finally, soybean oil is an economical choice. For cooks who are both cost-conscious and health-conscious, soybean oil is a useful pantry staple.

This story was sponsored by the United Soybean Board.

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