This surprising (to me, anyway) side-effect of frying sulfur-containing vegetables in vegetable oils is worth noting.
The study revealed that sulfur compounds significantly promote heat-induced trans-isomerization of UFAs in vegetable oils, especially when cooking temperatures is above 140°C. The addition of antioxidants significantly reduced the promotion of UFAs isomerization by isothiocyanates, whereas they did little to inhibit the promotion of isomerization by polysulfides. This explains that cooking polysulfide-rich vegetables such as garlic and onions in vegetable oil at high temperatures can generate TFAs. In fact, this study demonstrated that garlic and onions significantly promote the trans-isomerization of UFAs.
… “Release of TFAs under normal cooking conditions is expected to be minimal. Therefore, excessive caution is unnecessary,” concludes Dr. Honda, the corresponding author of this paper. “However, it is important to understand that cooking with ingredients rich in natural sulfur compounds may increase the risk of TFA intake.”
Isothyocyanates are present in ‘cruciferous’ vegetables such as cabbage, broccoli, etc. Polysulfides are present in onions, garlic, leeks etc, but also in cruciferous vegetables.
Hooray. Another great reason to refuse to eat any cruciferous vegies (especially broccoli and brussels sprouts and the truly execrable kale) that some want to insist on calling food.
Are you trying to kill me by serving THAT? I don’t want to die of TFA induced heart failure.
I often fry onions and garlic in olive oil to start making a soup or stew; and of course stir-frying naturally involves high heat and vegetable oil.
It’s interesting, and I think worth knowing, that these actions can create TFAs. Probably not a worry, but maybe something to consider if often eating stir-fried foods.
As noted in the research, the amount generated was not of great concern in usual circumstances.
“”Release of TFAs under normal cooking conditions is expected to be minimal. Therefore, excessive caution is unnecessary,” concludes Dr. Honda”
If someone had a diet more highly loaded with TFAs then caution would be advised. Stir frying has long been practiced in many Asian cuisines, the diets have been often praised for their health benefits as well.
As it is known, the dose makes the poison. Even browning meat creates some minimal amount of TFAs, also using polyunsaturated oils at high temps, such as those containing higher levels of linolenic acid can lead to isomerisation.
Frying onions and garlic. Forgot about that. If I am going to do it I use butter. Tastes better. I know Olive oil is supposed to be healthier but I just don’t like the taste.
And yet just about every food package in the Supermarket have vegetable oil in it. The Australian and New Zealand Department are not doing a very good job allowing this stuff to be sold to the public.
It has been clinical proven that vegetable oil is not good for you especially affecting your eyesight in later years. Maybe others, and yet manufacturers are still allowed to add it to just about all packaged food, including frozen meals.
The term “vegetable oil” is generic and could mean any one of a large number of individual plant-based oils or combinations of them. That generic term would include olive oil, which at present is considered nutritionally ‘healthy’.
Could you be more explicit about which specific oils are suspect, and point us to relevant research articles about studies indicating adverse effects?
Some links that provide some information about the risks of fat intakes and in particular Macular Degeneration (MD or AMD). Oils higher in Omega 6 are considered the culprits.
There are benefits from Omega 3 fatty acids intake, such as from fatty fish.
Ratios of greater than 6:1 (Omega 6 to Omega 3) are associated with greater risk of various types of Macular Degeneration. The Western diet tends to range from 10 to 20:1, while the Mediterranean diet is seen as beneficial to help avoid and reduce risk of MD at around 2 to 4:1. Oils high in Omega 6 fatty acids and low in Omega 3 should probably be avoided. We shouldn’t avoid Omega 6 oils, they are important to our health, it is just about keeping the ratio below 7:1.
Some oils often used in cooking that are higher in Omega 6 are Grapeseed oil, Cottonseed oil, safflower oil, soybean oil, and corn oil.
And just to add fat to the fire (pun intended) … when you’re on any kind of prescription drug, be aware that these healthy foods can have adverse interactions with some drugs:
If manufacturers were aware that vegetable oil is not good for our health, I am sure they would list olive oil it was included. It has been stated that no vegetable oils or seed oils are good for you. We really need the Australian New Zealand food watchers to start excluding these oils. (Doing their job) They are in most manufactured mixed packaged foods.
Evidence that seed oils are not automatically bad for you:
A lot of discussion about seed oils focuses on a purported imbalance of omega-3s and omega-6s in most modern diets, which are heavier in grains and seeds compared to those of early humans. Some influencers claim that our consumption of omega-6s far outweighs that of omega-3s and that we should aim for a 1:1 ratio. The evidence does not bear this out, Marklund says. In their study of linoleic acid and cardiovascular disease, researchers also looked at participants’ omega-3 levels. They found that the association between linoleic acid and cardiovascular risk was similar among participants with high or low levels of omega-3.
Marklund warns against focusing on ratios and instead on eating a healthy diet. “Omega-3 and omega-6 are necessary and are important, and we should probably eat more of both,” he says. “If people want to get the ratio closer to 1:1, the recommendation should not be to reduce omega-6, but rather to increase your omega-3 intake. Eat more walnuts or fatty fish.” Another food that contains a lot of omega-3, Marklund points out: canola oil.
In conclusion:
Seed oils can be part of both healthy and unhealthy diets. Instead of cutting out all foods containing seed oils, Marklund says, “consider eating less ultraprocessed food and more whole foods, fruit, and vegetables—and then use seed oils together with those.”
Whats the word on coconut oil? I was using that if frying, for ages. I’ve run out now (not that I am doing much frying anymore) and need to decide if I want more of it or not.
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