Are Vegetable and Seed Oils Bad for Your Health?

Important Points:

• Industrial Seed Oils
• Hydrogenated fat
• Omega 6
• Omega 3
• Linoleic acid
• Animal Fats

Are Vegetable and Seed Oils Bad for Your Health?

The consumption of vegetable oils has increased dramatically in the past century. We have been told otherwise, but industrial seed oils such as soybean, canola, and corn oils are not “heart healthy” at all. They do nothing good for our bodies and brains. In fact, plenty of research indicates that these oils are making us sick. Here we cover industrial seed oil history, the harm they do to your health, and what fats you should eat instead.

1. What Are Seed Oils?

Industrial seed oils are highly processed oils taken from soybeans, corn, rapeseed (the source of canola oil), cottonseed, and safflower seeds. They entered the American diet in the early 1900s.

2.  How Are Industrial Seed Oils Made?

The way industrial seed oils are made is anything but natural. Oils from soybeans, corn, cottonseed, safflower seeds, and rapeseeds must be refined, bleached, and deodorized. Only then are they fit to eat.

1. First, seeds are gathered from the soy, corn, cotton, safflower, and rapeseed plants.
2. Next, the seeds are heated to extremely high temperatures. This makes the unsaturated fatty acids in the seeds oxidize (react with oxygen and break down). That creates byproducts that harm human and animal health.
3. The seeds are then processed with a petroleum-based solvent, such as hexane, to squeeze out as much oil as possible.
4. Next, industrial seed oil makers use chemicals to deodorize the oils, which smell very bad once extracted. This deodorizing step produces trans fats.
5. Finally, more chemicals are added to improve the color of the industrial seed oils.

All in all, industrial seed oil processing makes an oil that is high in calories and low in nutrients. It contains chemical residues, trans fats, and oxidized byproducts.

3. Why are they bad for you?

Linoleic Acid Could be Increasing Our Risk of Obesity and Related Health Problems

In experiments in mice, raising linoleic acid intake from 1% to 8% may trigger brain signals that drive more eating and promote body fattening. Eating more linoleic acid seems to mask the feeling of fullness. It also seems to increase the size of fat cells.

•  Vegetable Oils Contain an Unnatural Amount of Omega-6 Fats

When it comes to omega-6, quality matters. Industrial seed oils are high in omega-6. But plenty of whole, fresh foods also contain omega-6 fatty acids naturally. These include nuts, poultry, and avocados.

Essential fatty acids are polyunsaturated fats (PUFA) that humans cannot make. So we must get them from food. They come in two kinds: omega-6 fatty acids and omega-3 fatty acids. Once eaten, omega-6 fatty acids turn into arachidonic acid and strong byproducts that mostly drive inflammation. These include prostaglandin E2 and leukotriene B4. Omega-3 fatty acids such as ALA, EPA, and DHA, on the other hand, turn into byproducts that fight inflammation.

A delicate balance between omega-6 and omega-3 fatty acids must be maintained in the body to promote optimal health. Eating a lot of omega-6 and little omega-3 throws your inflammation signals out of balance. The signals that fan inflammation outweigh the ones that calm it. That produces a state of chronic inflammation that contributes to numerous chronic disease processes.

• Vegetable Oils are Unnaturally Produced, Highly Refined, and Extracted Using Heat and Chemicals

Factory-made PUFA oils are produced with high heat and extreme pressure. This exposes the oil to all sorts of oxidative damage (damage from oxygen). Then the makers dump in chemical solvents to get every last drop of profitable oil out of the seeds, corn, or soy. Some of the chemical (usually hexane) stays in. Then yet another chemical is added to cover the stench of the rancid PUFA oil. In that process, the small amount of omega-3 in oils like canola actually turns into trans fatty acid. Last, BHT and BHA are added as chemical preservatives. Both are carcinogenic (cancer-causing). Why add them? Because processing wipes out the natural preservatives the food once had, such as the antioxidant vitamin E.

• Vegetable Oils Contribute to Excess Inflammation and Free Radical Damage. 

Polyunsaturated fats are very fragile and oxidize very easily. Heat, light, or oxygen makes the PUFA oxidize and form free radicals (unstable molecules that damage cells). That is hard to avoid when you are cooking with these fragile oils. And most restaurants use only these oils, not just for cooking but for extreme high-heat frying.

PUFAs cause too much inflammation in the body because of free radicals. These free radicals form when industrial oils (like vegetable and canola) are processed, and they make the oils rancid. Free radicals are loose and need a place to land. They attack cell membranes and red blood cells. They also damage DNA and RNA strands, which leads to cell mutations in the body’s tissues. In skin, it causes wrinkles and early aging. In blood vessels, they cause plaque to build up. In tissues and organs, it can set the stage for tumors to form. You get the idea. Free radicals are bad, bad news, and industrial PUFA oils are full of them.

•  Many Vegetable Oils are Hydrogenated and Can Be Filled with Trans Fats.

PUFAs are at their very worst when they are partially or fully hydrogenated. This chemical process takes place in factories. It is used to make PUFAs solid at room temperature and more “shelf stable”. Trans fat is the artery-clogging fat formed when vegetable oils are hardened. That is how margarine, vegetable shortening, and often vegan butters and cheeses are made. Trans fats block the making of prostacyclin, which your body needs to keep your blood flowing. When your arteries cannot make prostacyclin, blood clots form, and you may die suddenly.

4.  What Health Conditions are Linked to Industrial Seed Oils?

• Asthma: Eating industrial seed oils may raise your risk of asthma. Industrial seed oils are high in omega-6 fatty acids. Eating a lot of these compared with omega-3 fatty acids raises the inflammation signals associated with asthma.
• Autoimmune Disease: Industrial seed oils may promote autoimmunity, where the immune system attacks the body. They do it by raising the body’s omega-6-to-omega-3 ratio. They also add to oxidative stress and chronic inflammation.
• Cognition and Mental Health: Industrial seed oils are especially harmful to the brain. A high omega-6-to-omega-3 fatty acid ratio sets people up for depression, anxiety, cognitive decline (loss of thinking skills), and dementia. Eating canola oil is linked to worse memory and weaker learning in Alzheimer’s disease. Trans fats end up in industrial seed oils in two ways. Some form by accident from chemical and heat processing. Others are made on purpose through hydrogenation. Trans fats are associated with higher risks of dementia and, oddly enough, aggression.
• Diabetes and Obesity: Linoleic acid is the main fatty acid in industrial seed oils. Research in mice indicates that eating a lot of it changes nerve signaling in the brain. In the end, that increases eating and weight gain. In mice, a diet high in soybean oil causes obesity, insulin resistance, diabetes, and fatty liver disease. Some animal research also suggests that canola oil may cause insulin resistance.
• Heart Disease: Researcher James DiNicolantonio has put forward a theory. He calls it the “oxidized linoleic acid theory of coronary heart disease”. It links eating industrial seed oils rich in linoleic acid with heart and blood vessel disease (cardiovascular disease).
• IBS and IBD: Research suggests that industrial seed oils may harm gut health. This may contribute to conditions such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). In one study, mice fed a diet high in omega-6 fatty acids from corn oil had more gut bacteria that drive inflammation. These changes favor gut disease, among many other chronic diseases.
• Inflammation: A high omega-6 intake from industrial seed oils promotes chronic inflammation. Eating partially hydrogenated industrial seed oils is associated with higher C-reactive protein, TNF-alpha, and interleukin-6. So is eating plain soybean oil that is not hydrogenated. These are blood markers of body-wide inflammation.
• Infertility: About 9 percent of men and 11 percent of women in the United States have trouble having children. Many factors are driving soaring rates of infertility. One overlooked cause may be the large amount of industrial seed oils we eat. Infertile men have a significantly higher omega-6-to-omega-3 ratio than fertile men. In animal studies of female mammals, eating a lot of omega-6 fats causes poor reproductive results.
• Macular Degeneration: Industrial seed oils may be harmful to the eyes. A high intake of omega-6 fatty acids increases the risk of age-related macular degeneration. This eye disease causes vision loss that gets worse over time and ends in blindness. Too much omega-6 may contribute to eye problems in two ways. It promotes inflammation. It also pushes out the omega-3 fatty acid DHA, which is crucial for vision.
• Osteoarthritis: In people with osteoarthritis, there is an association between omega-6 fatty acids and synovitis. Synovitis is inflammation of the lining of the joint. On the other hand, MRI scans show that more omega-3 intake goes with less cartilage loss in the knee. Industrial seed oils add a large amount of omega-6 fatty acids to the diet. So avoiding these oils may be beneficial for those with or at risk of osteoarthritis.

5. Which Oils Should You Use for Cooking?

• Coconut Oil
• Tallow/ Suet (beef fat)
• Lard/Bacon Fat (pork fat)
• Butter
• Ghee
• Goose, Duck or Chicken Fat
• Extra-Virgin Olive Oil*
• Avocado Oil*
• Palm Oil
• Other fats (not always for cooking, but essential to good health) come from meats, eggs, dairy, and fish. Nuts are also good in moderation, since they are high in polyunsaturated fats.

* Olive oil and avocado oil are both high in monounsaturated fats, which are fairly stable. So they are best used with no heat or low heat. Avoid extreme high-heat cooking with them. They are also great in salad dressings, homemade mayonnaise, for drizzling, etc.

Note:

You can tell if an oil is chemically processed just by reading the label.

AVOID all fats and oils, and any products that contain them, if you see these processing terms ANYWHERE on ANY food label:

• Refined
• Hydrogenated
• Partially-Hydrogenated
• Cold-PROCESSED (do not confuse this trick phrase with Cold-PRESSED)

INSTEAD, look for these safer processing terms on your fat/oil labels:

• Organic
• First-cold pressed or Cold-Pressed Expeller-Pressed
• Unrefined
• Extra Virgin

6. The Bottom Line

If top health is your goal, then industrial seed oils have no place in your diet. Instead, cook with traditional animal fats. Get your omega-6s from whole foods such as nuts and poultry. Balance them out with omega-3 fatty acids from seafood, shellfish, and fish oil.

Related reading

• Conjugated Linoleic Acid: Is It Good for You?
• Heart Healthy Oils: Which Oils to Use
• 10 Types of Saturated Fats
• Why Vegetable Oil Seemed Healthy
• Omega-6 Vegetable Oils, Obesity and Insulin Resistance

Sources

1. Ramsden CE, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ. 2013. PMID 23386268
2. Ramsden CE, Zamora D, Majchrzak-Hong S, et al. Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ. 2016. PMID 27071971

Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026