Credible nutrition scientists have opposing views on whether omega 6 in vegetable oils is good for heart health. But who is right?
Part 1 of this series examined claims that omega 6 in vegetable oils causes ill health by increasing the risk for cancer, macular degeneration, Parkinson’s disease and inflammatory conditions, such as rheumatoid arthritis, ulcerative colitis and asthma. These claims, frequently expressed on the internet and in social media, were found to be baseless.
Part 2 will consider whether omega 6 increases or decreases the risk for coronary heart disease. Unlike the wild social media claims about omega 6, this issue is argued in the scientific literature with credible scientists on both sides. Whose argument is stronger?
The conventional wisdom
Leading heart health agencies such as the Heart Foundation, the American Heart Association and the World Health Organisation assert that polyunsaturated fats (mainly omega 6) are heart healthy and that they may be the ideal replacement for saturated and trans fats in the diet. The case appears to be strong:
• Polyunsaturated fat (mainly omega 6) has a beneficial effect on blood lipids. When saturated fat is replaced by polyunsaturated fat the level of serum LDL-cholesterol and the total cholesterol/HDL cholesterol ratio both fall, which is consistent with lower risk for coronary heart disease.
• Epidemiological studies indicate that polyunsaturated fat (mainly omega 6) is heart friendly. A pooled analysis of 11 prospective cohort studies conducted in Europe and the United States shows that replacing saturated fat with polyunsaturated fat lowers coronary risk more than other macronutrients.
• In randomised controlled trials coronary heart disease risk falls when saturated fat is replaced by polyunsaturated fat (mainly omega 6) – see Harvard’s meta-analysis.
So the conventional wisdom is based on three consistent lines of evidence with a rare meta-analysis of randomised controlled dietary trials sitting on top. Impressive. How could you argue against it?