Unlike traditional oils extracted from fruits, such as olive, coconut or avocado, vegetable oils from seeds are obtained through complex industrial processes, and are therefore a recent addition to the human diet.

We’ll see now Why Sunflower, Soy, Corn, and Other Oils Are Dangerous, especially when heated, and you will know the better alternatives for the kitchen.

The origin of vegetable oils

At the beginning of the 20th century, it was cooked mainly with traditional oils and animal fats. But new industrial processes allowed at that time to obtain low cost oil from different seeds, such as corn, sunflower, soybeans or rapeseed.

In a few decades, the consumption of animal fat was reduced and the intake of this new industrial fat, rich in polyunsaturated fatty acids.

In the 20th century, the consumption of animal fat was reduced and the intake of vegetable oil multiplied

The linoleic acid (Omega 6) is the main fatty acid in these oils, and while in ancient societies it represented 1-3% of total calories, in Western societies it has multiplied up to 8-10% (detail, detail).

We don’t yet know the impact of this change, but as this post indicates, Israel could be considered a dietary experiment of the effect of these oils on our health, by far surpassing Europe and the United States. And it seems that the result is problematic: high mortality from cardiovascular disease and cancer.

As traditional oils are displaced in favor of industrial ones, disease rates rise (study).

Polyunsaturated oils and heart health

Public health institutions They not only ignored this new danger, they encouraged it. Since polyunsaturated oils appeared to lower blood cholesterol in the short term, they generally recommended increasing their intake.

Now, however, we know that the relationship between cholesterol and cardiovascular disease is complicated, and lowering cholesterol doesn’t necessarily mean helping your heart.

In fact, recent reviews of studies from the 60-70s conclude that, contrary to what was reported at the time, replacing animal fats with polyunsaturated vegetable oils did not reduce mortality from cardiovascular disease, and in fact higher total mortality is observed in the groups that increased the consumption of vegetable oil (review, review).

Those who cut saturated fat in favor of vegetable oils suffered higher mortality

Linoleic acid has special easy to accumulate in our fabrics (study, study), and different studies show how the amount of linoleic acid we store has been increasing over the years (study, study, study, study, study). This has shifted the concentration of Omega 3 fatty acids, such as EPA and DHA (study).

For example, there is a clear correlation between the accumulation of linoleic acid and coronary heart disease (detail).

Correlation between levels of Omega 6 in tissues and mortality from cardiovascular disease

Linoleic acid also accumulates in the LDL particles that carry cholesterol, contributing to its oxidation. This oxidized cholesterol is especially atherogenic (detail).

Linoleic acid may contribute to the oxidation of LDL particles

This would explain the results of multiple studies where it is observed that raise linoleic acid, especially from vegetable oils, is usually associated with increased coronary risk (meta-analysis, study, study, study)

Obesity and other disorders

It is wrong to blame an individual factor for the obesity epidemic, but perhaps sugar has taken too much of the blame. Too much sugar is a problem, but the consumption of vegetable oil has grown much more.

Source: https://www.ncbi.nlm.nih.gov/pubmed/21367944

While total fat has remained relatively stable, added fat (vegetable oils to a greater extent) has skyrocketed in just a few decades (detail).

Total fat consumption (in the US) has remained stable, but vegetable oil intake has increased significantly

The soy oil is one of those that contributes more linoleic acid, and studies in mice indicate that it produces more fat build-up than coconut oil or fructose (study, study), including in the liver (study, study, study). In these animals, the canola oil it also increased their weight and impaired cognitive function (study).

The fatty acids we consume also impact the mitochondrial membrane (study), and an excess of linoleic acid could cause mitochondrial dysfunction (study).

And we have similar studies in humans:

  • Association between an increase in fatty liver and an increase in the Omega 6 / Omega 3 ratio (study, study), which improves by reducing this ratio (study).
  • A recent clinical trial shows greater inflammation and worse microbiota in those who increased the consumption of soybean oil.
  • Higher intake of canola or sunflower oils is associated with risk of metabolic syndrome (study).
  • In older adults, replace vegetable oils with olive oil improves cognitive function (study).

The Main Problem: Heat

All of the above said, small amounts of these oils used raw they shouldn’t be a big deal, and your main risk is in using them for cooking.

Heating these polyunsaturated oils triggers processes of hydrolysis, oxidation and polymerization, rapidly degrading its properties and generating problematic compounds (detail).

This effect is enhanced by using refined oils, lacking antioxidants that would mitigate the damage (detail).

Processes that deteriorate vegetable oil each time it is heated. Source: Impact of consumption and cooking manners of vegetable oils on cardiovascular diseases

The worst case scenario would come from reusing these degraded oils, and continued use of reheated oils is associated with higher levels of vascular inflammation, blood pressure and free radicals (study, study, study).

Best cooking oils

Within vegetable oils, not all are the same, and their effect will depend on their different fatty acids and the amount of antioxidants.

This combination will determine for example the induction time, an indicator of its oxidation resistance.

Induction time (or oxidative stability) of different types of oil. Source: https://www.researchgate.net/publication/321843217_Revealing_the_relationship_between_vegetable_oil_composition_and_oxidative_stability_A_multifactorial_approach

The oils of soy, corn and sunflower are the least recommended options, but we must also consider the variants. For example, the oleic high sunflower oil, and could be considered a cheap alternative to olive oil, undoubtedly the star of the kitchen.

This greater contribution of oleic acid makes it much more heat resistant (study, study) and reduces for example the oxidation of LDL particles that contribute to coronary heart disease (study).

As the graph above shows, extra virgin olive oil is more stable, but there are variations depending on the type of olive and production method. Coconut oil (and especially cold pressed virgin) is also a good option.

Another factor to consider is the production of aldehydes when cooking, and again the vegetable oils like sunflower and flax produce more of these potentially toxic compounds than olive oil (study).

In short, we could order the most common oils in a classification like the following.

Finally, olive oil and coconut oil are fairly even in terms of their effect on different health markers, although I lean more towards olive oilespecially if you live in a country where it is easily available.

Markers where coconut oil works best (left) and vice versa (right) Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5855206/

Conclusions

The fear of saturated fat and the obsession with lowering cholesterol has led to the wrong recommendation to prioritize industrial oils rich in polyunsaturated fatty acids, even though we do not seem to be well adapted.

Although they are not recommended in general, the main problem comes when cooking. To improve your health, keep in mind three simple proposals:

  1. Limit your intake of vegetable oils from seeds, especially those richest in linoleic acid, such as soy, corn or sunflower. If you use them, better raw.
  2. To cook, prioritize olive oil (study, study), coconut oil or, failing that, high oleic sunflower oil.
  3. Cut down on frying in your life, and when you cold, minimize the times you reuse the oil. If you eat out, keep in mind that they tend to use cheap oils and reuse the oil more than recommended.