In small amounts, vegetable oils are healthy, as they contain fats that are essential in our diets. But our consumption of vegetable oil has increased considerably, and the health effects of high intakes are a source of scientific debate.

What researchers agree on is that vegetable oils such as safflower, sunflower, corn, cottonseed and soybean oils, are rich in a type of fat known as linoleic acid. That acid can lower LDL or "bad" cholesterol when it replaces saturated fats in the diet which primarily come from animal sources.

Whether consuming vegetable oils ultimately improves health outcomes seems to be less clear. In observational studies, which don't prove cause and effect but look at relationships between variables such as food consumption and disease, linoleic acid intake is inversely associated with heart disease risk in a dose-response manner.

Those findings don't seem to be the final word on the subject. A meta-analysis of randomised clinical trials on the topic, published in the BMJ, concluded that although replacing saturated fat with vegetable oils does lower LDL cholesterol, it does not necessarily translate into decreased deaths from heart disease.