There are many types of oil or fat derived from animal or plant sources that we can use in cooking. Some of the most common oils are vegetable-based, but these have recently come under fire as less healthy than previously thought. What are the facts about vegetable oils?
The processed vegetable oils that we see on our shelves today are available as the result of several separate consequences. First, the general public sought a heart-healthy substitute for butter and lard. Second, the chemical process used to extract vegetable oils was invented. Prior to this invention, oils were all processed by mechanical means, with a press. Third, government subsidies helped farmers grow vegetables for oil. This, in turn, made the oils cheaper for the consumer.
Generally, vegetable oils are made from a mix of canola, soybean, corn, sunflower and safflower oils. The process of extraction involves many chemicals, and some manufacturers add coloring or bleach the oil to make it looks more appealing and uniform. Effectively, it's a highly processed food product. This alone is a red flag when discussing nutrition, as whole foods (or foods closest to their natural state) offer more beneficial nutrients without added ingredients.
In terms of content, vegetable oils contain high levels of polyunsaturated fats. Unsaturated fats are the heart-healthy type; however, the breakdown of these fats is what may be detrimental. There are two types of unsaturated fatty acids that are essential, which means that we need them, but the body can't synthesize them. These are the omega-3 and omega-6 fatty acids, which are named for their chemical structure. So we need both, and both have benefits, and ideally we would consume the two in a low ratio, as close to 1:1 as possible. Having this balance is vital, because omega-3 fatty acids are anti-inflammatory while omega-6s are pro-inflammatory. We do need some inflammation, but long-term, chronic inflammation is damaging.
Today, the western diet, which includes high levels of vegetable oils, is estimated to have a ratio as high as 16:1. Unbalanced levels of omega-6 to omega-3 fats have been correlated with increased chronic inflammation, autoimmune disease, cancer, and cardiovascular disease. An easy way to prevent this is to reduce omega-6 fatty acid intake.
While choosing an oil to cook or bake with, keep in mind that many vegetable oils are highly processed and, with frequent use, can cause inflammation in the body. Oils with the highest amount of omega-6 include corn, sunflower, soybean and cottonseed. Olive and palm oils, as well as saturated fats like butter, contain very little omega-6s.
Carolyn McAnlis, RDN, is a Registered Dietitian Nutritionist who has a special interest in preventing chronic disease through nutrition. She graduated from Syracuse University with a Bachelor of Science in Nutrition Science & Dietetics and a minor in Psychology. After completing a full-time dietetic internship at the University of Virginia Health System, she has developed a passion for convincing others that healthy food can be delicious through her blog A Dietitian in the Kitchen.