Most processed foods are made with seed oils like soybean oil, sunflower oil, or canola oil. Many people use these oils for their own cooking as well.
Unfortunately, these oils may be some of the most unhealthy, unnatural things in your diet. Some people think that seed oils are responsible for much of the degenerative disease we struggle with today.
When seed oil is heated during cooking, the polyunsaturated fat in it begins to break down into toxic aldehydes, like 4-HNE. These aldehydes are very harmful when consumed frequently, causing obesity, metabolic syndrome, and cancer in studies on mice. For that reason, seed oils can be very bad for you, especially when they are deep fried because this involves very high temperatures. The hotter the cooking temperature and the longer the seed oil stays very hot, the more the oil breaks down into toxic aldehydes. The very worst culprit for aldehyde exposure is deep fried restaurant food because they don’t change their deep fryer oil very frequently, typically. That means it has a ton of aldehydes in it.