Article at a Glance
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Linoleic acid is an essential omega-6 fatty acid that’s required in small amounts (1-2% of total calories).
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The average person today eats 6-10% or more of their calories from linoleic acid due to increasing consumption of vegetable oils made from seed crops.
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Excessive linoleic acid intake is associated with inflammation, obesity, heart disease, and more.
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Fortunately, it’s possible to reduce your stored tissue linoleic acid levels. The single most important change is to avoid seed oils and processed and prepared foods with high linoleic acid levels.
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Other practices like exercise and intermittent fasting likely speed up linoleic acid depletion, but only if you eat a low linoleic acid diet.
Introduction
Linoleic acid might sound like an obscure or highly technical topic, but it shouldn’t be. It makes up 6-10% of calories in modern diets, yet many people today are still unclear about its roles in health and disease [*,*].
In this in-depth guide, we’ll cover the relevant facts, history, and health effects of linoleic acid, provide a comprehensive list of foods high in this fatty acid, and offer practical, research-backed advice to lower your linoleic acid levels and recover from excessive intake.
What Is Linoleic Acid?
Linoleic acid is an omega-6 polyunsaturated fatty acid (PUFA) that occurs naturally in a wide variety of foods, but especially in many nuts, seeds, and seed oils [*].
As the main component of vegetable oils made from seed crops, linoleic acid is a significant source of calories in many processed foods. And like other fatty acids, it contributes to the “mouthfeel” or sensory properties of foods by carrying flavor compounds and altering textures [*].
Linoleic acid is liquid at room temperature, colorless or lightly straw-colored, and flavorless or slightly bitter [*,*,*]. It’s molecularly unstable and prone to oxidizing (breaking down) into byproducts during storage and heating, and the bitter taste increases when it becomes rancid [*,*].
As an omega-6 fatty acid, linoleic acid is one of two naturally occurring essential fatty acids (EFAs) humans must obtain through diet [*]. In other words, your body can’t produce it from other compounds in foods.
Another EFA, α-linolenic acid or alpha-linolenic acid, has a name that sounds similar but is actually an omega-3 fatty acid. Like linoleic acid, you must also obtain omega-3 fatty acids from your diet.
Another name for linoleic acid is C18:2 or C18:2n6 (omega-6) due to its chemical structure, which contains 18 carbon atoms and two double bonds.
It’s called a polyunsaturated fatty acid or PUFA because it contains more than one double bond. In contrast, monounsaturated fatty acids (commonly found in olive oil) have only one double bond.
The History and Discovery of Linoleic Acid
Linoleic acid was initially isolated from linseed oil in 1844 at the laboratory of Justus von Liebig, one of the founders of organic chemistry in Germany, by Swiss scientist Frédéric Sacc [*,*].
Until 1929, no one suspected that dietary fatty acids were essential for humans or other animals because scientists knew that fats could be synthesized (produced in the body) from carbohydrates in foods [*]. But that year, George Oswald Burr and Mildred Lawson Burr, scientists at the University of Minnesota, discovered through experiments with rats that linoleic acid is an essential nutrient.
In a paper published in the Journal of Biological Chemistry in 1929, the Burrs described an experiment in which rats were given a fat-free diet and developed symptoms that suggested a deficiency of a nutrient found in fats [*,*].
Through additional experimentation, George and Mildred Burr discovered that the missing nutrient was linoleic acid [*]. They published a second paper in 1930 that demonstrated linoleic acid is an essential fatty acid (also the first use of the term), meaning it’s required for proper growth and prevention of disease in rats.
Linoleic acid is also essential for humans, but this hypothesis took several more decades to prove conclusively. The first convincing evidence came in the 1950s, when other researchers noted skin abnormalities in infants fed a low-fat diet that resolved when linoleic acid was added [*].
And later, in the 1960s, patients consuming long-term parenteral (IV) nutrition devoid of linoleic acid developed skin rashes and other signs of essential fatty acid deficiency, which also reversed after the addition of linoleic acid [*].
Linoleic Acid and Your Health
Linoleic acid is an essential nutrient, but deficiencies are extremely rare. (In fact, overconsumption of linoleic acid is a much more common issue today.)
The only documented instances of linoleic acid deficiency occur in [*,*]:
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Infants who are given formula that doesn’t contain essential fatty acids like linoleic acid
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Seriously ill patients on parenteral (IV) nutrition
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People who are starving or severely malnourished
The symptoms of deficiency include dermatitis (skin rash and irritation), alopecia (hair loss), visible lightening of the hair, poor wound healing, and an increased risk of infections [*]. In younger people, linoleic acid deficiency can stunt growth.
Why You Don’t Need to Worry About Linoleic Acid Deficiency
Researchers estimate that you need around 1-2% of your daily caloric intake from linoleic acid to prevent deficiency [*]. For an adult eating 2,000 calories per day, that’s approximately 2-3 grams of linoleic acid per day, which you can easily obtain from:
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A tablespoon-sized serving of dried sunflower kernels (over 3 grams of linoleic acid) [*]
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A half-ounce serving of pecans (nearly 3 grams of linoleic acid) [*]
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A half-ounce serving of dehulled sesame seeds (over 2.5 grams of linoleic acid) [*]
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An ounce of raw cashews (2.2 grams of linoleic acid) [*]
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A half-ounce serving of shelled pistachios (slightly under 2 grams of linoleic acid) [*]
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Three and a half ounces of cooked corn kernels (about 1.5 grams of linoleic acid) [*]
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A roasted chicken thigh weighing 3.5 ounces (a little under 1.5 grams of linoleic acid) [*]
Many other foods contain trace amounts of linoleic acid, which is another reason deficiency is so rare — even if you never intentionally eat linoleic acid, there’s virtually zero chance of developing a deficiency.
The Unprecedented Increase in Linoleic Acid Intake
Although low amounts of linoleic acid are essential to prevent deficiencies, the average person today eats around 6-10% of their overall calories from linoleic acid [*,*].
The main reason for this increase is because of the dramatic global rise in vegetable oil consumption, particularly soybean oil and sunflower oil [*]:
Before the 20th century, people obtained adequate linoleic acid levels from whole foods. But the introduction of vegetable oils and industrial seed oils resulted in much higher levels of linoleic acid intake.
For example, soybean oil, commonly found in processed foods and used in restaurants, contains about 55% linoleic acid [*]. And since 1909, human consumption of these vegetable oils high in linoleic acid has increased from virtually zero to as much as 20% of overall calories [*].
Is Linoleic Acid Good or Bad?
Low amounts of 1-2% linoleic acid are necessary for survival, but research links higher intakes to health problems, including inflammation, heart disease, cancer, dementia and other neurological disorders, diabetes, and obesity [*,*,*,*].
And the average person today is eating far more linoleic acid than at any other time in history. Until the 20th century, most people didn’t consume vegetable oils or seed oils high in linoleic acid — they easily obtained the necessary amounts from nuts and grains, and trace amounts in other foods, including meat, eggs, and dairy.
According to a paper from the American Journal of Clinical Nutrition, per capita consumption of soybean oil (which contains approximately 55% linoleic acid) increased 1000-fold from 1909 to 1999, along with increases in other industrial omega-6 seed oils that weren’t widely available before the 20th century [*].
As a direct result of eating more oils high in linoleic acid, most people are now consuming 6-10% or more of their calories from linoleic acid, and nutritional surveys suggest intakes will continue to increase [*,*,*].
So, why is this such a problem? Because it’s an omega-6 polyunsaturated fatty acid, linoleic acid is inherently unstable. It oxidizes (breaks down) more readily than most other fats — this is true during manufacturing, storage, transportation, and cooking as well as in your body after you eat it [*,*,*,*,*].
And since your body incorporates it directly into cellular membranes, excess linoleic acid bioaccumulates (builds up) in cells over time, resulting in instability and inflammation at the cellular level [*,*,*].
Finally, overconsuming linoleic acid also creates an imbalance between omega-6 and omega-3 fats in your body and depletes anti-inflammatory omega-3s in tissues [*].
Researchers think that humans naturally evolved to consume an equal ratio of these fats, but many people today now consume 20 times higher levels of omega-6 than omega-3 fats [*].
Eating too much linoleic acid disrupts healthy cellular function and contributes to inflammation [*,*]. Over-consuming inflammatory omega-6 linoleic acid can also reduce tissue levels of anti-inflammatory omega-3s, causing more inflammation and exacerbating this imbalance [*].
Next, we’ll examine peer-reviewed studies that explore the health effects of consuming too much linoleic acid to understand how this fatty acid affects your health over time.
Linoleic Acid and Heart Health
When you consume a diet high in linoleic acid, it results in higher levels of linoleic acid in cells and tissues, including [*]:
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Erythrocytes (red blood cells)
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Thrombocytes (platelets)
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Cholesterol
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The endothelium (blood vessel linings)
These changes are linked to an increased risk of atherosclerosis and other types of fatal cardiovascular disease [*].
But what about the claim that high-linoleic vegetable and seed oils are supposed to be good for your heart?
The idea that linoleic acid in vegetable oils was “heart-healthy” originally came from experiments conducted in the 1950s-1970s.
But recently, United States National Institutes of Health (NIH) researcher Christopher Ramsden used modern statistical analysis and recovered data from the same experiments, which included nearly 11,000 participants, to re-evaluate the original findings on linoleic acid.
After reviewing the results of the Rose Corn Oil Trial, the Sydney Diet Heart Study, the Minnesota Coronary Experiment, and the LA Veterans heart health study, the Ramsden group found no benefit and consistent evidence of harm from increasing dietary intake of linoleic acid [*,*,*].
Importantly, each of these studies initially sought to demonstrate the benefits of linoleic acid consumption, yet their results did the opposite. And despite not being recent, they’re the only randomized controlled trials (RCTs) of their kind that investigated the effects of increasing linoleic acid on heart disease risk and all-cause mortality (death).
More recent large-scale studies on the effects of linoleic acid use observational or epidemiological methods to determine population-wide results through correlation, but without any randomization.
As a result, their findings are mixed (some showing evidence of harm, others of benefit), which may be due to the “healthy observer” effect [*].
In other words, because public health officials touted omega-6 vegetable oils as healthy for decades, people who generally listen to public health advice about tobacco, alcohol, and trans fats are also more likely to consume high-linoleic-acid diets. This skews observational data in a way that doesn’t occur in well-designed RCTs and reduces the reliability of newer, non-RCT findings [*].
However, a plethora of experimental evidence illuminates the reasons for Ramsden’s findings.
Linoleic Acid and Cardiovascular Disease: Summary of Experimental Evidence
Linoleic acid is less stable than other fatty acids and is more prone to oxidation (breakdown).
In other words, when linoleic acid gets incorporated into LDL (low-density lipoprotein, a type of cholesterol), this process results in increased formation of oxidized LDL molecules in the circulatory system [*]. And oxidized LDL cholesterol is directly linked with inflammation and the formation of arterial plaques [*].
Here’s a summary of other research findings that show the implications of a high linoleic acid diet for heart health [*]:
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Linoleic acid levels in adipose (fatty) tissues and blood platelets positively correlate with cardiovascular disease.
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Patients with cardiovascular disease have higher concentrations of linoleic acid in their plasma than the general population.
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Compared to healthy patients, increased levels of linoleic acid oxidation products occur in the LDL and plasma of patients with atherosclerosis (hardening of the arteries).
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Higher amounts of linoleic acid oxidation byproducts have been found in arterial plaques, and the degree of oxidation correlates directly with the severity of atherosclerosis.
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Linoleic acid is the most abundant fat occurring in arterial plaques.
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Linoleic acid and its byproducts have been demonstrated to induce direct toxic effects on the endothelium (blood vessel lining).
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Ultrasound studies of healthy patients with high levels of 9-HODE (a linoleic acid oxidation byproduct) in carotid arteries also show signs of atherosclerosis.
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Individuals who die from sudden cardiac death tend to have more linoleic acid in their coronary arteries versus controls.
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A meta-analysis by Ramsden, et al. of randomized controlled trials in humans found that substituting omega-6 linoleic acid in place of saturated fat and trans-fats increases all-cause mortality as well as deaths from heart disease [*].
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Dietary changes that increase monounsaturated fat or decrease omega-6 linoleic acid are shown to decrease the likelihood of LDL oxidizing.
