Some vegetable oils are not as heart-healthy as they claim to be, according to a November 2013 study in the Canadian Medical Association Journal.Researchers looked at the two major families of polyunsaturated fatty acids—omega-3 linolenic acid and omega-6 linoleic acid—to determine whether they both pull their own weight in terms of reducing the risk of heart disease. The researchers found that the benefits from vegetable oils are derived from oils with a high omega-3 fatty acid content. They stated that oils with a high omega-6 composition with very little omega-3, such as corn and safflower oil, had few health benefits.

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The findings from the study address the uncertainty regarding the health benefits associated with oils rich in omega-6s but low in omega-3s. The research referenced a clinical trial that was published in February 2013, which included one intervention group that swapped out saturated fats for omega-6-rich safflower oil or safflower oil margarine.

Compared to the control group who maintained their saturated fat intake, the intervention group’s cholesterol levels decreased by eight to 13 percent.These findings were expected. Surprisingly, however, the intervention group had higher rates of death from heart disease.

The authors of the study recommended conducting further research to gain a better understanding of the health benefits associated with oils. Until then, they suggest that health claims be modified such that foods rich in omega-6 linoleic acid but poor in omega-3s be excluded from any heart-healthy claims.

The nutritional value of vegetable oils is dependent on which type of polyunsaturated fat is most prominent, and that varies with every vegetable oil. While there is evidence that oils rich in omega-3s are associated with reduced cholesterol levels and prevention of heart disease, there is no such association with omega-6s. However, that does not mean you should dump your vegetable oils.

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Another study that was published in June 2013 reviewed 15 clinical trials that included almost 500 adults to determine the association between the composition of fatty acid intake and inflammation. The researchers found no association between a diet high in omega-6 linoleic acid and increased inflammation.Based on the strongest, most recent evidence, this is what we know about vegetable oil intake:

  • The American Heart Association promotes the use of vegetable oils for cooking. They recommend consuming 2 to 4 tablespoons of vegetable oils per day.
  • Focus on limiting your intake of saturated fat to less than 10 percent of your overall calories. A high intake of saturated fat is associated with increased serum cholesterol levels and an increased risk of death from coronary heart disease. This three-way relationship was first demonstrated in 1980 by Ancel Keys, and since then, clinical trials have supported the benefits associated with replacing saturated fats with vegetable oils. Major sources of saturated fats include dairy products, beef, pork, coconut oil and palm oil.
  • Consume more omega-3s. The typical western diet is heavy on omega-6s and low on omega-3s. A lower ratio of omega-6s to omega-3s is ideal because the metabolism of both polyunsaturated fats is inter-connected. Omega-3s promote heart health by acting as an anti-thrombotic agent, inhibiting the growth of atherosclerotic plaques, stimulating nitric oxide, lowering cholesterol and acting as an anti-inflammatory agent. Good sources of omega-3 fats include walnut oil, flaxseed oil and canola oil.

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Brigid Titgemeier, nutrition assistant at the Cleveland Clinic Wellness Institute, contributed to this article