Vegetable oils, like corn, rapeseed, sunflower or soybean oils, are rich in omega-6 fatty acids.
One omega-6 fatty acid is linoleic acid (LA), and is included in the category of essential fatty acids, with the word essential meaning that the body cannot produce it and the only means of getting it is through diet.
Although LA is essential and we need it in our diet to be healthy, an excess of this fatty acid is also damaging to our health.
To be more precise, the negative effect is due to an imbalanced omega-6/omega-3 ratio (too much vegetable oil and too little fatty fish). A healthy omega-6 to omega-3 ratio is considered to be something between 1:1 to 4:1. This is far from the average 16:1 in western diets.
Going back to linoleic acid… LA is a precursor of arachidonic acid and this one is involved in promoting inflammation. So, a large omega-6 to omega-3 ratio results in excess inflammation and, in addition, interferes with the beneficial health effects of omega-3 fatty acids. The latter is partly explained because omega-6 and omega-3 use the same enzymes to be metabolised by our bodies. Too much omega-6 using these enzymes means there aren’t enough of them for the little omega-3 we may have thrown in our gut. And here, in the gut, is where that excess LA is putting a lot of stress and where some of our microbes can do something about it.
What they do is metabolise linoleic acid to produce what is called conjugated linoleic acid (CLA). On top of reducing the amounts of linoleic acid, some types of CLA have been reported to be anti-inflammatory, anticarcinogenic, increase insulin sensitivity (protection from diabetes), decrease atherosclerosis (protection from cardiovascular disease) and decrease adiposity (excessive body fat). Brilliant!
As always, the ability to produce CLA varies a great deal from person to person depending on the types and amounts of microbes they have, which is obvious because they are the ones doing the job. If you have the ones efficiently converting LAs into CLAs (have the genes for it) you are in a good position.