Over the past century, our consumption of seed oils has risen dramatically. Seed oils are in everything from packaged snacks to nut milks to plant-based vege-meats. The most common seed oils are canola (rapeseed) oil, soybean oil, corn oil, sunflower seed oil, cottonseed oil, safflower oil, peanut oil, grapeseed oil, and rice bran oil.
Seed oils are a subset of vegetable oils, but not all vegetable oil is bad. Palm oil, coconut oil, olive oil and avocado oil are four common types of vegetable oil; the most common vegetable oil in the world is palm oil. These other vegetable oils are preferable because they can be produced by cold pressing, and they have lower levels of the linoleic acid that is a cause for concern in seed oils.
Seed oils are produced using industrial methods, including solvents, high heat, and mechanical pressure. They are a relatively recent addition to the human diet because, before large-scale industrial processing capabilities existed, such oil simply could not be economically produced for human consumption.
How Seed Oils Are Extracted
While other vegetables, such as olives and avocadoes, will release their oil under mechanical pressure alone, seed oils must be extracted under high heat, using a chemical solvent. The solvent used in extracting seed oils is basically gasoline; it is classified based upon the number of carbon atoms in the molecule, ranging from five to eight. Pentane, hexane, heptane, and octane can all be used for oil extraction, but hexane is currently the most widely used for that purpose.
Oil solubility in solvent increases with temperature; the higher the temperature, the more oil recovered, and the faster it can be recovered. But there are obvious risks to using hexane at high temperatures; hexane is extremely flammable. Strict precautions must be taken to avoid fire and minimize the risk of explosions at seed oil extraction plants.
There are three major steps in seed oil extraction: (1) extracting the oil; (2) getting the solvent out of the meal and the oil, (3) toasting the meal. It is not possible to remove all of the hexane from the oil; some hexane remains in the product that will go on to be consumed as food, although it is believed to be less than 1%. The residual content of hexane in seed oils after processing is not even regulated by the FDA.
The oilseed processing industry is under pressure to switch to solvents such as alcohol or water. But the industry is resisting because there are major economic disadvantages to being limited to alcohol and water in the oil extraction process.
How Seed Oils Are Bad for Your Health
High consumption of seed oils seems to correlate with metabolic syndrome: obesity, high blood pressure, high cholesterol, heart disease, high blood sugar, diabetes, etc. It also correlates with cancer and other health problems.
The Linoleic Acid Problem
What is linoleic acid? For one thing, it is what we make flooring out of. The linguistic connection between “linoleum” and linoleic acid is not coincidental. The main components of Linoleum are derivatives of linoleic acid and alpha-linolenic acid.
When we compare the linoleic acid levels of the various types of vegetable oils, we see that seed oils generally have much higher levels of linoleic acid:
Palm 10%
Olive 12%
Avocado 13%
Canola 21%
Peanut 30%
Rice bran 30%
Cottonseed 53%
Soybean 55%
Corn 56%
Sunflower 68%
Grape seed 71%
a. Linoleic Acid and Immune Cells
A 2004 study comparing the effects of bathing T lymphocyte cells in a high concentration of either linoleic acid or oleic acid (an omega-9 fatty acid found in olive oil and many other foods) found that linoleic acid caused immunologically harmful effects. The authors expressed concern that seed oils high in linoleic acid could be immunosuppressive, and may harm the immune function of critically ill patients when given as part of hospital nutrition.
The same researchers conducted a similar study in 2006 and found, once again, that linoleic acid was toxic to lymphocyte cells, which it killed by producing free radicals and preventing mitochondria from producing energy.
b. Linoleic Acid and Retinal Cells
In 2021, after observing increased linoleic acid levels in the feces of patients with severe eye inflammations, researchers examined the effects of linoleic acid in retinal cells and several types of immune cells. The study found that linoleic acid inhibited the function of immune cells called dendritic cells and T helper cells, caused cell death in dendritic cells, and decreased the functioning of retinal pigment epithelial cells. Two studies from 1996 and 2000 also found that linoleic acid is highly toxic to cells from cows’ eye lenses, known as bovine epithelial lens cells.
c. Linoleic Acid, LDL and Hardening of the Arteries
Research suggests that oxidation in low-density lipoprotein (LDL), which is what doctors call the “bad cholesterol,” causes atherosclerosis (hardening of the arteries). Some of the researchers even insist that atherosclerosis cannot occur without oxidized LDL.
In a 1993 experiment, researchers measured the rate and extent of LDL oxidation as it related to the content of oleic acid and linoleic acid found in their cholesterol. The researchers found that higher levels of oleic acid and lower levels of linoleic acid helped to prevent LDL oxidation and vice versa — that lower levels of oleic acid and higher levels of linoleic acid increased rates of LDL oxidation.
In a series of experiments published in 2002, scientists fed groups of mice oxidized linoleic acid byproducts, which result from normal heating of linoleic acid during cooking. They found increased oxidative stress (cellular damage) and larger cardiovascular lesions in most of the mice given the oxidized byproducts.
In a 2017 experiment, mice receiving a mere 9 to 18 milligrams per day of oxidized linoleic acid had lower levels of liver ppar-alpha—low levels of ppar-alpha are associated with fatty liver, impaired glucose metabolism, and other metabolic issues—and lower plasma levels of HDL, which is what doctors call "good cholesterol.”
While previous studies have shown that oxidized LDL can lower triglycerides, which some researchers consider positive for cardiovascular health, these researchers concluded that longer-term oxidized linoleic acid consumption could lead to hardening of the arteries.
d. Linoleic Acid and Reproductive Germ Cells
A 2010 study examining the effects of linoleic acid supplementation on bovine oocytes (immature egg cells from cows) found that the omega-6 fatty acid interfered with the maturation of the cells and inhibited embryo development. This evidence suggests that linoleic acid in follicular fluid is likely associated with the declining fertility rates documented in farm animals—as well as in humans—both of which are consuming more linoleic acid than ever before. In 2016, a different research group conducted a study using similar methods and found the same results.
e. Linoleic Acid, Neurological Development, and Alzheimer’s
In a 2008 animal study, researchers raised the question of whether current high omega-6 fatty acid intake is contributing to poor neurodevelopment. This study on young piglets provided two different diets designed to investigate the effects of early infant nutrition: one with required amounts of linoleic acid to prevent deficiency (1.2% of overall calories) versus another with high amounts (10.7%, which is equivalent to modern human intakes).
The low-intake group had healthy, normal brain development, but the group consuming linoleic acid levels of 10.7% of overall calories had impaired and altered neurological development.
In a 2017 study using mice predisposed to developing characteristics of Alzheimer's, researchers gave mice regular food or food supplemented with canola oil, which increased dietary linoleic acid, for six months. The study showed that increasing linoleic acid intake led to a significant increase in body weight, impairments in working memory and brain structure, and more beta-amyloid plaque development (which is associated with developing Alzheimer’s disease in humans) compared to the control group.
f. Linoleic Acid, Metabolism, and Obesity
A 1993 study found that in rats eating standardized diets that contained either safflower oil (high in linoleic acid), olive oil, or edible tallow as an additional fat source, the rats consuming the most linoleic acid gained approximately 16% more weight compared to the olive oil group and 36% more weight than the tallow group — even though all rats received the same overall caloric intake.
In a 2012 mouse study, researchers hypothesized that elevated linoleic acid would promote obesity through overactivation of the endocannabinoid system. They designed their experiment to model 20th-century increases of human linoleic acid consumption, changes that “closely correlate with increasing prevalence rates of obesity," and found that higher linoleic acid intakes did increase food intake and fat storage. However, reducing linoleic acid reversed these effects in the mice.
In a 2017 experiment, researchers divided male mice into groups receiving a low-fat diet or a high-fat diet containing 1%, 15%, or 22.5% of calories from linoleic acid, with the rest from saturated fat. Compared to both the 1% linoleic acid group and the low-fat diet, rats receiving the 22.5% linoleic acid diet had: 1) Greater body weight gain, 2) Decreased activity levels, 3) Heightened insulin resistance
The authors concluded that "in male mice, linoleic acid induces obesity and insulin resistance and reduces activity more than saturated fat, supporting the hypothesis that increased linoleic acid intake may be a contributor to the obesity epidemic."
A separate 2019 study found that when mice were given a diet with 8% linoleic acid for eight weeks, their body weight increased significantly compared to a group given 1% linoleic acid. Mice consuming more linoleic acid and more glucose together consumed more calories and gained more weight for the number of calories consumed than the other groups.
In a 2015 study, researchers gave young rats a control diet with 3.16% of energy from linoleic acid, or 1.36% of energy from linoleic acid. They later switched all the animals to a Western-style diet and monitored body composition, blood sugar, and other variables. The 1.36% linoleic acid group accumulated 27% less fat from the Western diet and had lower triglycerides, suggesting that decreasing linoleic acid intake early in life may help prevent obesity and metabolic problems later.
g. Linoleic Acid and Cancer
While there are no well-designed long-term human trials on the effect of dietary linoleic acid and cancer outcomes, some animal studies seem to indicate that omega-6 fatty acid promotes tumor growth and is linked to breast cancer and lung cancer. Researchers have also found a higher rate of mammary tumor growth in rats when linoleic acid constitutes 10% or more of caloric intake.
There are clearly many problems with consuming too much linoleic acid. Linoleic acid might make great flooring, but it does not make very good food. Aside from the problem of linoleic acid, there are other issues with consuming seed oils.
Modern Americans have gotten their fatty acids out of balance.
Historically, our diet contained a 1:1 ratio of n-6 and n-3 fatty acids. But in Western society today we’re eating up to 20 times more omega-6’s than omega-3 fatty acids. Research links diets higher in omega-6’s to diseases such as chronic inflammation, cancer, heart disease, Alzheimer’s, obesity, diabetes, and other forms of neurological and psychiatric issues. Given the large amount of omega-6 in Western diets, it is impossible to counter it with omega-3 and stay in the proper balance.
Seed Oils are Highly Processed, and that Makes a Difference.
The industrial process of extracting seed oils uses high temperatures, chemical deodorizers, and petroleum-based solvents—essentially gasoline—to extract oils from seeds. This strips the oil of its natural nutrients and antioxidants, while at the same time creating harmful trans-fats. Processors also add synthetic chemicals such TBHQ, BHA, and BHT in order to extend the shelf life and prevent the oxidation of these oils, but these substances are carcinogens, and are banned in Japan, the European Union, Canada, Australia, and New Zealand.
Seed Oils Cause Oxidative Stress in the Body.
Seed oils high in omega-6 fatty acids are susceptible to going rancid; the processing of massive amounts of food in factories and restaurants almost ensures that some percentage of processed food will be fried in oil that is already effectively rancid.
Moreover, consuming large quantities of seed oils creates an imbalance between free radicals (molecules missing an electron) and antioxidants in your body. High concentrations of free radicals in the body cause cellular damage that can lead to cancer, diabetes, Parkinson’s disease, cardiovascular diseases, cataracts, asthma, hypertension, arthritis, and Alzheimer’s disease.
Seed oils change our bodies at the molecular level. One study suggests from 1959 to 2008 our fat cell composition of linoleic acid increased by two and a half times, reflecting our change in diet. This means our bodies and cells themselves are more vulnerable to oxidation and rancidity.
Seed Oils Contain Trans-Fats.
Although trans-fats do occur in nature, they are being consumed at a much higher rate than ever before in history. Trans-fats elevate LDL, which, as noted above, is the bad cholesterol. LDL tremendously increases your risk of coronary heart disease, and other cardiovascular illnesses and conditions.
Seed Oils Might Negatively Impact Male Fertility.
Studies have found that men who were infertile had more than two times as much omega-6 fatty acids as Omega-3 in their blood and sperm as compared to fertile men. Another study found that 4-hydroxynonenal, a toxic byproduct of omega-6 fatty acids, can damage human sperm. By contrast, higher intake of omega-3 fatty acids positively correlated with greater sperm concentration, motility, and morphology.
Seed Oils Might Impact Maternal and Fetal Health in Pregnant Women.
Animal studies have shown that high intake of omega-6s, especially those with linoleic acid, can lower levels of the omega–3 DHA, which is very important for fetal brain development and cognitive function. In addition, an animal study found that linoleic acid intake during late stages of pregnancy increased risk of premature labor (before full term). Additional research is needed to understand how seed oil consumption impacts pregnancy outcomes and fetal health in pregnant women.
How Can I Reduce Seed Oils and High Linoleic Acid in my Diet?
From the foregoing discussion it should be clear that cutting down on seed oil consumption is as important for your health as avoiding high fructose corn syrup, and getting plenty of water, exercise, fresh air and sunlight. Avoiding seed oils will not be easy; it will take some work, but the health rewards will be worth it.
First, avoid eating out too often. Because seed oils generally cost less than cold press oils, restaurants tend to use seed oils for frying their food. If we prepare our own food at home, we know what it is in it, and we choose the oils we use.
Second, when you are eating out, which is unavoidable in certain circumstances, such as when traveling, avoid eating too much fried food. Also, it is a good practice to ask the waiter what type of oil is used in the restaurant. He or she typically will not know, but she can ask; the feedback will eventually reach the restaurant owners and operators, who will begin to learn that people are concerned about the health problems associated with seed oils.
Third, cut down on highly processed food. If you are eating raw fruits and vegetable, they will not have seed oils in them.
Fourth, when you are buying processed food, read the nutrition label so that you know what you are eating. If the nutrition label shows one of the seed oils, look for a substitute. Corn chips, potato chips, and similar crunchy snacks are a common source of seed oils.
Mexican-style tortilla chips are very popular in the American southwest; one of the most popular brands is “On the Border,” produced by the Mexican restaurant chain. If you read the label on that package, you’ll notice that it lists most if not all of the seed oils. This is because they might be using any of those commodity oils to deep fry their chips at any given time, and likely they also blend oils, so that they don’t even know exactly which of the seed oils, and in what proportions, are in their vats.
On the other hand, some tortilla chip makers are already advertising that their chips are fried in avocado oil. I recently ran across a tortilla chip made by Siete that prominently advertised on the bag that they were fried in avocado oil.
Fifth, ask questions. When you start asking questions, you will find that health-oriented food stores—Whole Foods, Wild Oats, Trader Joes, and many locally owned, non-chain stores—usually have someone on the staff who will have been trained about alternatives to seed oils (and genetically modified food (GMOs), and high fructose corn syrup (HFCS), and gluten, etc.). Take advantage of their training.
With a little work you will soon be cutting way down on seed oils, and reaping the health benefits of avoiding them.
For those of you who learn visually, we are adding this lecture by Dr. Chris Knobbe, of the University of Texas Southwestern Medical School at Dallas:
“Behold, I will bring to it health and healing, and I will heal them and reveal to them abundance of prosperity and security.” Jer. 33:6