Vegetable Oils: Why They’re Not as Healthy as You Think


Vegetable Oils: Why They’re Not as Healthy as You Think

Most plant foods are healthy and vegetable oils are extracted from plants – so why wouldn’t they be healthy too? For years, we’ve been told that vegetable oils, the golden-yellow oils that line the shelves of your local grocery store, are heart healthy and that they’re better for you than natural sources of fat such as butter. Even the American Heart Association recommends using these oils as a heart-healthy substitute for butter. But times are changing. Now, the whole idea that vegetable oils are a healthier option is falling into question.

What Are Vegetable Oils Made Of?

Vegetable oils are extracted from seeds that come from plants. To extract the oil and get a ready-to-use product, manufacturers go through a series of steps. These steps include heating the seeds to high temperatures, extraction of the oils using a solvent, application of more heat, and the addition of chemicals to deodorize and enhance the color of the final product.

That’s already not sounding very healthy, but vegetable oils are also high in polyunsaturated fats. For many years, the medical world has proclaimed polyunsaturated fats to be more heart-healthy than saturated fat, like the fats you find in meat, dairy products, as well as a few plant-based sources, like coconut oil and palm oil.

The problem is polyunsaturated fats contains two varieties of fatty acids – omega-3s and omega-6s. Most of the processed vegetable oils you buy at the grocery store, like corn oil, soybean oil, sunflower oil, safflower oil, and grapeseed oil, are much higher in omega-6 fatty acids than omega-3.  This is problematic because we need a healthy balance of omega-3 to omega-6 fatty acids and people who eat a typical Western diet get far more omega-6s than they do omega-3s. As you know, omega-3s are abundant in sources like fatty fish, flaxseed, sesame seeds, and walnuts. Ideally, we should get a ratio of omega-6 to omega-3 of close to one to one. In reality, the average person consumes an omega-6 to omega-3 ratio of as high as 20 to 1.

Vegetable Oils and Inflammation

Why is consuming so many omega-6 fatty acids relative to omega-3s an issue? Research suggests this imbalance is linked with low-grade inflammation inside tissues and blood vessels. Short-term inflammation is a good thing if you have an injury, such as a cut. Inflammation activates your immune system in a way that helps your body heal. However, ongoing, low-grade inflammation is harmful. It’s now becoming apparent that low-grade inflammation is the driver of many chronic health problems, including heart disease and stroke, autoimmune diseases, and cancer. Diet is only one factor that fuels inflammation, but it’s an important one.

If you read the ingredient list of most processed foods you buy at the grocery store, you’ll see that most packaged snacks and ready-to-eat items are made with omega-6 rich oils, mainly soybean oil.  If you’re eating a lot of processed foods, you’re almost surely getting far more omega-6 fats than you are omega-3.

What Happens to Vegetable Oils When You Heat Them?

Since most of these vegetable oils are used as cooking oils, you might wonder what happens when you heat them. Research shows when you expose these oils to high temperatures, they produce chemicals called aldehydes. The aldehydes these oils produce, at the very least, aren’t healthy. Plus, studies have linked them with cancer. In fact, a researcher in the area, Martin Gootveld points out that fish and chips fried in vegetable oil have up to 200 times more aldehydes than the World Health Organization allows. Unfortunately, many people and restaurants still fry with these oils.

Oils to Avoid

Vegetable oil blends

Corn oil

Cottonseed oil

Soybean oil

Safflower oil

Sunflower oil

Grapeseed oil

Peanut oil

Margarine (made with vegetable oils)

Safer Alternatives to Vegetable Oils

Since it looks like most of the oils you find at the grocery store aren’t healthy– what should you use? How about olive oil? Olive oil contains mostly monounsaturated fatty acids. Monounsaturated fats are more stable than polyunsaturated ones and research suggests that olive oil is a heart-healthy option. Unfortunately, extra-virgin olive oil has a relatively low smoke point, making it a poor choice for cooking at high temperatures. Therefore, it’s best to use it at room temperature, for salad dressings, or low-temperature applications like sautéing and baking.

For higher temperature cooking, coconut oil is an option. Yes, it’s high in saturated fat but recent research questions whether saturated fats from sources like coconut oil are damaging to the heart after all. Plus, there are different types of saturated fatty acids. The types in coconut oil are lauric acid and myrisitic acid. Research shows myristic acid slightly increases LDL-cholesterol but much of that increase is due to a rise in HDL rather than LDL.

Don’t Go Overboard with Coconut Oil

Contrary to what you may have read online, it’s probably not a smart idea to consume large amounts of coconut oil until more research comes out about its effect on cholesterol and heart disease. Moderation is best. Yet, some health experts even question whether elevated cholesterol is a strong risk factor for heart disease, especially considering many people who have heart attacks have normal cholesterol.

The focus is now turning to the role of inflammation and damage to the inner walls of blood vessels plays in stroke and heart attack. That’s important since the high omega-6 fatty acid content of vegetable oils may contribute to inflammation. All in all, coconut oil in moderation for high-temperature cooking is a safer choice than polyunsaturated vegetable oils. After all, vegetables are high in omega-6s and form aldehydes when you heat them.

The Bottom Line

It’s hard to completely avoid omega-6-rich vegetable oils but reduce your exposure as much as possible. Unfortunately, they’re in most packaged foods and are the main oil lower end restaurants cook with. When is the last time you went to a restaurant that cooked with coconut oil? For one, it’s too expensive. Still, you won’t have to use these oils when you cook at home. Keep olive oil and coconut oil on hand and leave the vegetable oils in cheap plastic bottles at the store.



Biochem Pharmacol. 2009 Mar 15;77(6):937-46. doi: 10.1016/j.bcp.2008.10.020. Epub 2008 Oct 28.

Today’s Dietician. Today’s Dietitian Vol. 16 No. 11 P. 32.

Circulation. 2004; 109: II-2-II-10 doi: 10.1161/01.CIR.0000129535.04194.38

Sott.net. “Heart surgeon speaks out on what really causes heart disease”

Circulation. 2004; 109: II-2-II-10 doi: 10.1161/01.CIR.0000129535.04194.38.

Am J Clin Nutr. ajcn.27725. January 13, 2010.

Ann N Y Acad Sci. 2005 Dec;1055:179-92.


Related Articles By Cathe:

Food Fakery: It’s as Close as Your Grocery Store

Dietary Fat Made Simple

Good Fats Versus Bad Fats: The Problem With Vegetable Oils

What Are Omega-9 Fats and Why Are They Important?

Olive Oil is Healthy, but is It Safe to Cook With?


Hi, I'm Cathe

I want to help you get in the best shape of your life and stay healthy with my workout videos, DVDs and Free Weekly Newsletter. Here are several ways you can watch and work out to my exercise videos and purchase my fitness products:

Get Your Free Weekly Cathe Friedrich Newsletter

Get free weekly tips on Fitness, Health, Weight Loss and Nutrition delivered directly to your email inbox. Plus get Special Cathe Product Offers and learn about What’s New at Cathe Dot Com.

Enter your email address below to start receiving my free weekly updates. Don’t worry…I guarantee 100% privacy. Your information will not be shared and you can easily unsubscribe whenever you like. Our Privacy Policy