Are Vegetable Oils Healthy for You?

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Processed seed and vegetable oils, including canola oil, increase inflammation, and chronic disease.

As the consumption of processed vegetable and seed oils has increased dramatically over the past 100 years, so have rates of obesity and chronic diseases. While there are many potential causes for this uptick in health conditions, one often-underlooked area is America’s overconsumption of vegetable oils.

Although previous dietary recommendations have stated that vegetable oils are heart-healthy, more recent studies have shown that these industrially-produced oils are causing more harm to human health than good.

In this article, we’ll outline the differences between saturated and unsaturated fats and how the oxidation of vegetable oils creates inflammation in the body.

What Are Vegetable Oils? 

Vegetable and seed oils include corn, soybean, canola, peanut, cottonseed, safflower, sunflower, grapeseed, and vegetable oils. 

Traditionally, humans consumed fats that didn’t require much processing to eat them, including butter and olive oil. Vegetable oils are a relatively new addition to our diets and require a lot more processing to become ready to consume. As we’ll see, this introduces a whole host of health problems.

The Basics of Saturated and Unsaturated Fats

Fats are generally classified by whether they are saturated or unsaturated. Unsaturated fats can be monounsaturated (MUFA) or polyunsaturated fatty acids (PUFA). PUFA’s can then be primarily classified into omega-3 and omega-6 fatty acids.  

For a brief chemistry lesson, saturated fats do not have double bonds and can stack upon each other. This “stackability” is what allows saturated fat-containing foods to stay solid at room temperature — like butter, for instance.

When fat is fully saturated, it means that there is no room for any other molecules to bind to it, leading saturated fats to be highly stable structures. Saturated fats are most commonly found in animal products, such as butter, dairy, and meat, as well as coconut products.

MUFA’s are somewhat stable, as they have one double bond, which means there’s one open space for another molecule to bind to it. Commonly, free radicals will bind to that open spot, which are harmful molecules that damage cells and accelerate aging. MUFAs are typically found in plant foods, like olive oil and avocados.

Lastly, PUFA’s have multiple double bonds, making them highly unstable and prone to oxidation when exposed to heat or light. Instability and oxidation are the primary reasons why industrially-produced seed and vegetable oils can cause inflammation in the body. 

The process of making vegetable oils includes mechanical pressing, bathing in a hexane solution, degumming, bleaching, and deodorizing before it can become ready to eat. These steps introduce high heat or light, causing the oils to oxidize or become rancid, even before they hit the grocery store shelves. 

Essentially, vegetable and seed oils will be full of oxidized fats even before you cook with them. Additionally, as these types of oils, like canola or soybean, are commonly used to cook with and fry foods in restaurants, the high-heat cooking introduces even more inflammatory compounds that can damage your cells upon consumption. 

Vegetable and seed oils are already oxidized before they get to the grocery store.

Vegetable Oils and Chronic Disease 

There are two main mechanisms by which vegetable oils can create inflammation and increase the risk of chronic disease. The first is through the oils’ susceptibility to oxidation, which causes DNA, cellular, and membrane damage, leading to accelerated aging and disease development. .  

Secondly, vegetable oils are very high in omega-6 fatty acids. In general, omega-3 fats are anti-inflammatory, while omega-6 fats tend to promote inflammation. 

Omega-3 fats are primarily found in fatty fish, with the three main omega-3 fats being EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid), and ALA (alpha-linolenic acid). Omega-6 fats are found in nuts, seeds, and their oils, primarily in the form of linoleic acid.

Both of these fats are essential in our bodies, and we need them in our diet. However, the ratios of omega-3 to omega-6 fats have become skewed in an unfavorable way over the past few decades. 

Our ancestors consumed a ratio of approximately 1:1 of omega-3 to omega-6 in their diets. Today, the ratio may be as high as 1:20. Many researchers say a ratio of about 1:4 for omega-3 to omega-6 would be ideal. 

This sharp increase in omega-6 consumption leads to significant changes in our cell membranes, which are made up of PUFA’s. A diet high in omega-6 fats — especially oxidized omega-6 fats — but low in omega-3’s will lead to cell membranes being primarily composed of oxidized and pro-inflammatory fats. 

One of the omega-6 fats, arachidonic acid (AA), gets converted into a set of hormones called eicosanoids, which upregulate pro-inflammatory signaling processes that influence the development of conditions like obesity, inflammatory bowel disease, and cardiovascular disease.

Through these two mechanisms — oxidation and dysregulated omega fatty acid ratios — the risk of several health conditions increases with the overconsumption of processed vegetable and seed oils: 

  • Cognitive decline: A systematic review found that a greater omega-6 to omega-3 ratio is associated with an increased risk of cognitive disorders like dementia. Additionally, canola oil consumption led to impaired memory and a loss of synaptic integrity in an animal study.
  • Mental health disorders: A high omega-6 and low omega-3 intake is linked to an increased risk of depression and anxiety. 
  • Infertility: A high dietary intake of omega-6 fats is linked to fertility-related challenges in both men and women. 
  • Cardiovascular disease: Although some PUFA’s, like omega-3 fats, are linked to a reduced risk of developing heart disease, oxidized omega-6 fats increase the amount of inflammatory plaque in the arteries, which is linked to cardiovascular disease
  • Diabetes: High omega-6 intake increases insulin resistance, a driving factor in the development of type 2 diabetes. 
  • Obesity: A high omega-6 to omega-3 ratio increases leptin resistance and levels of “white fat,” both of which cause weight gain

Dietary Fats: What Should You Eat?Healthy fats include salmon, avocado, olive oil, and whole nuts and seeds.

To achieve better health, a good goal would be to focus on lowering your ratio of omega-6 to omega-3 fats in the diet, as the leading source of dietary omega-6’s is from vegetable and seed oils.

Some ways to balance out this ratio include reducing your intake of vegetable and seed oils while increasing your intake of fatty fish (such as salmon, sardines, tuna, and mackerel), walnuts, chia seeds, and flaxseeds. 

Keep in mind that oxidation can occur in healthy fats, which happens if you cook with olive oil at very high heat or if your fish oil pills go rancid from heat exposure. 

Unsaturated fats, especially PUFAs, are fragile fats and should be treated as much. This means only using unsaturated fats, like olive oil, sesame oil, walnut oil, or macadamia nut oil, for dressings or when cooking at very low temperatures. Also, it would be wise to avoid processed vegetable oils altogether, as they have already become oxidized even before you cook with them. 

Research has shown that extra-virgin olive oil is likely the healthiest fat choice, as it’s full of MUFA’s, antioxidants, and anti-inflammatory polyphenols. However, if you want to cook with high heat, other good choices are those made up of saturated fats, as these fats are stable and unable to oxidize easily. These would include coconut oil, grass-fed butter, or ghee. 

Key Takeaway

  • Vegetable oil consumption has sharply increased in recent decades; these oils include canola, soybean, corn, safflower, peanut, cottonseed, sunflower, and vegetable oil. 
  • The vegetable and seed oils become oxidized during processing and manufacturing due to their unstable polyunsaturated fatty acid structure, which increases oxidative damage to our cells and DNA. 
  • Vegetable oils also are high in omega-6 fats; a dietary ratio with too many omega-6 fats and too few omega-3 fats is linked to several health conditions, including heart disease, obesity, dementia, infertility, and mood disorders. 
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