Eating the wrong oil may promote breast cancer? Which cooking oil should I choose?

Recently a friend asked me: I just saw a scientific news report saying that eating linoleic acid can promote breast cancer ! I know that linoleic acid is an ingredient in cooking oil. My mother has breast cancer. Can she still eat cooking oil?

What kind of oil to eat has always been a topic of concern to the general public. But after so many years, many people still don't understand why different oils have different health effects.

Let’s put aside the oil’s thermal stability, freshness, fat-soluble vitamin content, etc. and just talk about fatty acids .

We learned in middle school that the main component of oil is neutral fat (or triglyceride, triglyceride), which is a chemical substance formed by a glycerol molecule + 3 fatty acids. All fats are the same in terms of glycerol. But what exactly are the 3 fatty acids? There are big differences in different oils.

There are many kinds of fatty acids in food. Some are long, some are short (different carbon chain lengths), some are straight, some are bent (different saturation levels), and some have different bends (ω-6 or ω-3 series). These are so complicated that people who have not studied chemistry will feel dizzy.

Simply put, different fatty acids play different roles in human metabolism.

Some promote inflammation, while others inhibit it. The ratio between them is important and involves the energy metabolism and inflammatory response of cells.

In addition, the saturation of fatty acids must be appropriate. If the saturation is too low, it is easy to be damaged by oxidation. If the saturation is too high, it may affect the function of cell membranes.

Back to this research news. Linoleic acid is a common fatty acid in cooking oil.

It is not good to say that linoleic acid is an essential fatty acid , that is, it is a nutrient necessary for life. Without it, people cannot live well.

However, as the saying goes, "too much is as bad as too little", even the best things can cause trouble if eaten too much. Most Chinese people now have enough linoleic acid, and even often eat too much, so few people say it is good.

I looked at the research news mentioned by the friend at the beginning of the article [1]. This latest study said that linoleic acid activates mTORC1 through a fatty acid binding protein (FABP5), thereby promoting the progression of "triple-negative breast cancer." Case studies have also found that this connection does exist. Patients with high levels of linoleic acid in their bodies also have more FABP5.

After discovering the connection between linoleic acid and these metabolic pathways, the researchers conducted an animal experiment to verify it.

They designed two diets for the experimental animals. The calories were the same, and the ratios of carbohydrates, fats and proteins were the same, which were normal for mice. The only difference was the oil added to the feed. In other words, the ratio of fatty acids in the mice's diet was different.

One group was given safflower oil (omega-6 series) rich in linoleic acid, and the other group was given flaxseed oil and fish oil (omega-3 series) rich in alpha-linolenic acid.

Simply put, the other nutritional components of these two sets of feeds are the same, but the ratios of ω-6 and ω-3 fatty acids are different.

If this ratio is different, the level of inflammatory response and metabolic pattern will be different. Omega-6 fatty acids promote inflammatory response, while omega-3 fatty acids reduce inflammatory response.

The researchers found that increasing the ratio of ω-6 to ω-3 in the mouse feed was enough to increase FABP5 in the mice, and mTORC1 was significantly activated after injection of triple-negative breast cancer cells.

I said to this friend: This study suggests that for some patients (such as this specific breast cancer patient), linoleic acid really should not be consumed too much . I wonder if your mother has triple-negative breast cancer. If so, she may need to adjust the type of oil she eats.

In addition, for people who always have acne or whose skin is prone to pimples, their body's inflammatory response is too high, and they may need to eat less linoleic acid.

This friend asked:

I understand now. Linoleic acid is a pro-inflammatory ingredient. So which oils contain more linoleic acid? I want my mother to avoid this pitfall immediately.

I said: Mainly in certain vegetable oils and oilseeds[2].

Safflower seed oil has the highest linoleic acid content, reaching over 70%.

Then there are sunflower oil and corn oil , which can reach more than 60%. Wheat germ oil and grape seed oil also belong to this category.

After that are traditional peanut oil, cottonseed oil, sesame oil , etc., which can reach 40%~50%.

The linoleic acid content of rapeseed oil is less than 20%, while that of tea seed oil and olive oil is even lower, less than 10%.

Soybean oil and walnut oil also contain a lot of linoleic acid, reaching more than 50%, but they also contain α-linolenic acid of the ω-3 series, so it is less likely to cause the problem of imbalance between the two series.

The friend asked again:

There are so many varieties of oil nowadays, for example, grape seed oil, avocado oil, pumpkin seed oil, wheat germ oil, and rice oil. What types of oil are they?

Avocado oil is a high oleic acid, low linoleic acid oil, the same type as olive oil.

Rice bran oil is also called rice bran oil , which is the oil in rice germ. The linoleic acid content is slightly lower, at about 35%. Pumpkin seed oil is similar to it.

Grapeseed oil and wheat germ oil are both high-linoleic oils, the same type as corn oil. Linoleic acid can be as high as 70% in the fat of watermelon seeds .

There are two strategies for adjusting the ratio of ω-6 and ω-3 fatty acids.

The first strategy: reduce ω-6 fatty acids, that is, reduce linoleic acid.

Replace those vegetable oils with too much linoleic acid with less linoleic acid. Reducing omega-6 is equivalent to reducing the ratio of omega-6 to omega-3 series.

For example, by replacing high-linoleic acid sunflower oil and ordinary peanut oil with high-oleic acid rapeseed oil, high-oleic acid peanut oil, high-oleic acid soybean oil, as well as tea seed oil, olive oil, avocado oil, etc., the intake of linoleic acid can be reduced.

(Oleic acid is neither omega-6 nor omega-3, it is omega-9, a monounsaturated fatty acid, and it is not pro-inflammatory .)

A friend asked:

When it comes to rapeseed oil, are low erucic acid and high oleic acid the same thing? Why do some rapeseed oils in supermarkets say they are low erucic acid, some say they are double low, and some say they are high oleic acid?

Since animal experiments have found that a large amount of erucic acid may be harmful to the myocardium and that too much glucosinolate may affect thyroid health, China has promoted "double-low" rapeseed oil with low erucic acid and low glucosinolate for decades. The rapeseed oil sold in supermarkets is double-low rapeseed oil. This type of rapeseed oil has a low linoleic acid content and a high oleic acid content, and is very cost-effective.

A recent epidemiological study found that among Americans who consume less vegetable oil and more butter, those who consume more rapeseed oil have a lower risk of cancer; eating an extra 5 grams of rapeseed oil per day is associated with a 15% lower risk of death, while there is no such benefit if corn oil or safflower oil is consumed [3].

The so-called "high oleic acid rapeseed oil" is a high-quality variety developed by Chinese agricultural scientists. The oleic acid content is ten percentage points higher than that of ordinary low-erucic acid rapeseed oil, and can even reach more than 75%. It also contains a small amount of α-linolenic acid, and the fatty acid ratio is better than that of olive oil.

Moreover, the content of vitamin E and vitamin K in my country's rapeseed oil is much higher than that in olive oil, and all indicators are superior.

The friend asked again:

Do melon seeds, peanuts, nuts, etc. also contain linoleic acid?

I said: That's right, the fatty acids in nuts and roasted snacks also need to be controlled.

People who want to control linoleic acid should not eat too much watermelon seeds and sunflower seeds, nor should they eat too much roasted peanuts and other fried food. Watermelon seeds are a super high linoleic acid food, with linoleic acid in fat reaching 70%, comparable to safflower seed oil. Some literature mentions that these seeds are also foods that promote acne . If they are fried dry and fragrant, the pro-inflammatory effect may be even stronger.

Among nuts, walnuts and pine nuts have a relatively friendly ratio of ω-6 to ω-3 fatty acids. Macadamia nuts, almonds, and pistachios have a similar fatty acid ratio to olive oil and can be eaten when controlling linoleic acid.

The second strategy: add ω-3 fatty acids, that is, add fatty acids such as α-linolenic acid, EPA, and DHA.

Sources rich in alpha-linolenic acid include flaxseed oil, perilla seed oil, and peony seed oil.

Marine fish and carnivorous freshwater fish are rich in EPA and DHA. In fact, you don’t have to buy salmon, tuna, etc. Cheap hairtail, yellow croaker, saury, etc., as well as freshwater sea bass, mandarin fish, etc., are all fine as long as you eat them twice a week.

If we take both approaches, we can adjust the ω-6/ω-3 fatty acid ratio relatively quickly.

The friend said: "I understand. I think it's not that difficult to operate. I'll go change the cooking oil for my mother."

I said: Linoleic acid is not the devil. Since it is an essential fatty acid for the human body, it is necessary to eat it .

In some cases, linoleic acid may have a protective effect on organisms. For example, studies have found that linoleic acid helps maintain intestinal immune function in animals with low nutritional supply levels[4]. For another example, linoleic acid also has an inhibitory effect on the ability of the S protein of the new coronavirus to bind to the pathogenicity[5]. There are many other health effects.

The main problem is that many people consume too much linoleic acid...especially when they have certain medical conditions.

Finally, a reminder: When choosing and consuming cooking oil, remember four things:

Eat less oil, control the temperature, diversify, and consider your physical condition.

Eat less oil: control the total amount. No matter how good the oil is, it is only 99.9% pure fat, and eating too much will easily make you fat.

Control the temperature: No matter how good the oil is, oxidation polymerization will occur and harmful substances will be produced when frying at high temperature or cooking with oil smoke.

Diversification: We have already told you about the fatty acid characteristics of common oils. You should eat different types of fatty acids. Don't just focus on one type of oil.

It depends on your physical condition: people with high inflammatory response should lower the ratio of ω-6/ω-3 fatty acids. Conversely, people who are thin, have poor appetite and low inflammatory response can moderately increase this ratio.

You must understand that it is not a good or bad thing for fatty acids. The key is what you lack. What you lack is good; what you have in excess is bad. Everything needs to be balanced. And people with different physiques need different balances.