The consumption of vegetable oils has increased dramatically in the past century. Most mainstream health professionals consider them healthy, but vegetable oils may cause health problems. Their health effects vary depending on what fatty acids they contain, what plants they are extracted from and how they are processed.
What Are They and How Are They Made?
Edible oils extracted from plants are commonly known as vegetable oils.
In addition to their use in cooking and baking, they’re found in processed foods, including salad dressings, margarine, mayonnaise and cookies.
Common vegetable oils include soybean oil, sunflower oil, olive oil and coconut oil.
Refined vegetable oils were not available until the 20th century, when the technology to extract them became available.
These are extracted from plants using either a chemical solvent or oil mill. Then they are often purified, refined and sometimes chemically altered.
Health-conscious consumers prefer oils that are made by crushing or pressing plants or seeds, rather than those produced using chemicals.
Edible plant oils are commonly known as vegetable oils. The oil is often extracted with chemical solvents or by crushing or pressing the plants or their seeds.
Consumption Has Increased Drastically
In the past century, the consumption of vegetable oils has increased at the expense of other fats such as butter.
The graph below shows how the consumption of polyunsaturated fats (mainly omega-6) in the US has increased to levels that are higher than ever.
Photo Source: Stephan Guyenet.
They are often labeled “heart-healthy” and recommended as an alternative to sources of saturated fat, such as butter, lard and tallow.
The reason vegetable oils are considered heart-healthy is that studies consistently link polyunsaturated fat to a reduced risk of heart problems, compared to saturated fat (1).
Despite their potential health benefits, some scientists are worried about how much of these oils people are consuming.
These concerns mostly apply to oils that contain a lot of omega-6 fats, as explained in the next chapter.
The consumption of vegetable oils increased drastically in the last century. While some vegetable oils have been linked to health benefits, there are concerns about the excessive intake of omega-6.
You May Want to Avoid Vegetable Oils High in Omega-6
It’s important to note that not all plant oils are bad. For example, coconut oil and olive oil are both excellent.
The plant oils that you should avoid due to their high omega-6 content include:
- Soybean oil
- Canola oil
- Corn oil
- Cottonseed oil
- Sunflower oil
- Peanut oil
- Sesame oil
- Rice bran oil
Both omega-6 and omega-3 fatty acids are essential fatty acids, meaning that you need some of them in your diet because your body can’t produce them.
Throughout evolution, humans got omega-3 and omega-6 in a certain ratio. While this ratio differed between populations, it’s estimated to have been about 1:1.
However, in the past century or so, this ratio in the Western diet has shifted dramatically and may be as high as 20:1 (2).
Scientists have hypothesized that too much omega-6, relative to omega-3, may contribute to chronic inflammation (3).
Chronic inflammation is an underlying factor in some of the most common Western diseases, such as cardiovascular disease, cancer, diabetes and arthritis.
Observational studies have also associated a high intake of omega-6 fat to an increased risk of obesity, heart disease, arthritis and inflammatory bowel disease (4).
However, these associations don’t necessarily imply a causal relationship.
Studies investigating the effects of feeding people omega-6 fat generally do not support the idea that these fats increase inflammation in the body (5).
Scientists do not fully understand what effects omega-6 fats have on the body, and more studies are needed.
However, if you are concerned, avoid oils or margarine that contain oils high in omega-6 fats. Olive oil is a good example of a healthy cooking oil that’s low in omega-6.
Some vegetable oils are high in omega-6 fatty acids. Scientists have hypothesized that eating too much omega-6 can lead to increased inflammation in the body and potentially contribute to disease.
These Oils Are Easily Oxidized
Saturated, monounsaturated or polyunsaturated fats differ by the number of double bonds in their chemical structure.
- Saturated fats contain no double bonds
- Monounsaturated fats contain one double bond
- Polyunsaturated fats contain two or more double bonds
The problem with polyunsaturated fats is that all these double bonds make them susceptible to oxidation. The fatty acids react with oxygen in the atmosphere and start deteriorating.
The fat you eat isn’t only stored as fat tissue or burned for energy, it’s also incorporated into cell membranes.
If you have a lot of polyunsaturated fatty acids in your body, your cell membranes are more sensitive to oxidation.
Basically, you’ve got your body loaded with very fragile fatty acids that can easily be degraded to form harmful compounds (8).
For this reason, it may be best to eat polyunsaturated fats in moderation. Vary your diet by eating a mix of healthy saturated, monounsaturated and polyunsaturated fats.
Oils that are high in polyunsaturated fats are susceptible to oxidation, both on the shelf and inside your body.