Are you familiar with linoleic acid? If you’ve heard about it from Dr. Joe Mercola, you’ve seen it calledĚýĚý˛ą˛Ô»ĺĚýĚýthe one true cause of all chronic illness. But if your go-to source of information isĚý, you’ve been told that it promotes healthy brain function, boosts the immune system, and reduces your risk of cardiovascular disease, as long as you get it from organic, non-GMO sources. Which is it?
Neither Mercola nor Axe is a credible source of information. Mercola is one of the worst pushers of health misinformation online, scaring his readers with nonsenseĚý, while selling every dietary supplement under the sun as an alternative to modern healthcare. Axe, meanwhile, isĚýĚýwho likewise makes preposterous claims and peddles dangerous, unproven “all-natural” remedies. Both men have an incredible reach online, but which one of these broken clocks happens to be right in this case?
If the word “omega-3” is familiar to you, you may have heard of omega-6 fatty acids as well, and linoleic acid is by far the most common of these in our diet. Figuring out what the optimal intake of linoleic acid is, however, has proven to be a lot more difficult than either Mercola or Axe understands.
A dramatic shift in fat consumption
Although dietary fats as a broad category have often been demonized, we do need to consume them. They provide us with energy, they help our brain work, and they are needed to absorb the fat-soluble vitamins A, D, E, and K.
What we have moved away from is overconsuming saturated fats. These fats, which often come from animal sources, are usually solid at room temperature. They include butter and lard, but also palm and coconut oils. The reason they are called “saturated” has to do with chemistry. The carbon atoms they are made of are saturated in hydrogen atoms. When they sacrifice some of these hydrogen atoms to make double bonds with each other, they become unsaturated.
Unsaturated fats are commonly found in seed oils (like canola and soybean oils) and nuts. When they have a single double bond, they are known as monounsaturated; when they have many, they are polyunsaturated. These polyunsaturated fats are crucial toĚýĚýhappening at the molecular level.
There has been a dramatic shift in fat consumption in North America over the past century. Animal fats like lard, tallow, and butter used to dominate our diet; but in the 1800s, entrepreneurs became interested in a waste product of the cotton industry: cottonseed oil. Initially used in lamps, an edible version was subsequently developed by Procter & Gamble and they called itĚý. It was marketed as just as useful as animal fats for cooking but cheaper. This opened the door wide to vegetable oils and shortenings being used in the food industry, and from 1909 to 1999, we sawĚýĚýin the consumption of these unsaturated fats by Americans.
Some of them, called trans fats, would eventually be banned, as they were linked to an increased risk of coronary artery disease and diabetes. Others, like omega-3s, received a health halo, going as far as being sold as dietary supplements. One of these unsaturated fats that have quietly been receiving more and more attention isĚýlinoleic acid, a type of omega-6 polyunsaturated fatty acid. (It should not be confused with alpha-linolenic acid—notice the additional “n” near the end—which is an omega-3 fatty acid.)
Linoleic acid is found in large amounts in corn oil, cottonseed oil, grapeseed oil, sesame oil, soybean oil, sunflower oil, and walnut oil, in the range ofĚýĚýof linoleic acid per 100 grams of oil. By comparison, the popular olive oil has 9.8 grams of linoleic acid per 100 grams.
Nuts and seeds are also good sources of linoleic acid, and animals that have been fed grain will often carry a significant amount of linoleic acid in their meat. Because of its omnipresence in modern Western diets, Americans currently consume on averageĚýĚýof linoleic acid every day, which translates to 6% of their daily energy needs.
Researchers have wondered what this shift away from saturated fats and toward a diet rich in omega-6 fatty acids is doing to our health.
Eating your heart out
One of the concerns with linoleic acid—and one that is brought up by Mercola, dripping with fearmongering—is that it could promote inflammation. The process of inflammation is normal and quite helpful for our tissues to heal and to defend ourselves against harmful microorganisms; but chronic and excessive inflammation is damaging and causes health problems. Linoleic acid is transformed in the body into derivatives that have been linked to inflammation, hence the theoretical risk that too much linoleic acid in the diet could be responsible for chronic inflammation.
But this speculation hasĚýĚý. In 2012, aĚýĚýof the evidence coming from the University of Illinois concluded that there was “virtually no evidence” from randomized controlled trials in healthy humans to show that adding linoleic acid to the diet increased the concentration of inflammatory markers in the blood. Just because linoleic acidĚýcanĚýbe metabolized into pro-inflammatory molecules doesn’t mean that it will; there can be compensatory mechanisms, and certain metabolic pathways can already be saturated, meaning that more linoleic acid will not translate into more of these metabolites. Molecular biology is complex, and our intuition can often be simplistic.
On the other hand, there is the claim that omega-6 fatty acids like linoleic acid are actually good for our cardiovascular system, warding off strokes and plaque deposits in our arteries. Summaries of the evidence in the 2010s came toĚý, sowing confusion, but it does now look like linoleic acid is overall good for heart health (seeĚýĚý˛ą˛Ô»ĺĚý, for example).
Other associations are much less clear. There isĚýĚýas to whether or not linoleic acid makes asthma worse in children, and while the omega-6 fatty acid is most probably not a cancer-causing agent, it appears to promote the growth of some cancerous tumours in some species underĚýsome conditions.
The reasons for our lack of certainty on these important health issues are the same ones we see with nutrition science globally. We do not eat linoleic acid; we consume oils, both uncooked and heated up to high temperatures, that contain linoleic acid, among other types of fat. We ingest a wide range of molecules that both increase and decrease our risk of bad health outcomes, and our diet changes from year to year. Observational studies are plenty but they can’t prove causation, whereas clinical trials where participants are forced to eat a certain way are harder to conduct. These complexities breed murkiness.
Given this confusing mountain of data, researchers and clinicians are left trying to answer a very important question: just how much linoleic acidĚýshouldĚýwe consume, and how much can we safely ingest?
A balancing act
ĚýIt is tempting to turn to populations that are recognized for living longer than the rest of us—“blue zone” regions like Okinawa, Sardinia, and Ikaria in Greece—and ask them how much linoleic acid they’re getting from their daily diet. Based on published estimates, these people consumeĚýĚýthan Americans do. While this shows that lower levels are compatible with longevity, we should not infer from this that we should lower our intake of linoleic acid. The people who live in blue zones may have different energy needs and their genetic background will differ from ours. Seeking a clear answer by limiting ourselves to analyzing their diet is myopic.
Should we stop eating linoleic acid as a precaution? Absolutely not: linoleic acid, like a vitamin, is “essential,” meaning that our body cannot synthesize it on its own. We need to get it from our diet, otherwise we develop skin lesions. But how little is needed for health remains a topic of debate, with some sayingĚýof our daily energy intake should come from linoleic acid and others arguing forĚý. (By comparison, the average for Americans currently is 6%.)
Some have tried to shift the debate toward a target ratio of omega-6 fatty acids to omega-3 fatty acids, but this ratio has beenĚý. Different omega-6 fatty acids play different functions in the body. To bundle them all up into a total that we need to aim for ignores biology. Moreover, we can calculate one ratio based on our food consumption and another one based on what ends up circulating in the blood, and they will not be the same. For example, levels of linoleic acid measured in the blood areĚýĚýby smoking and alcohol consumption. So, which ratio is the informative one, if any?
The short answer is that scientists do not yet know what we should aim for with regards to our daily consumption of linoleic acid, though a commonly cited acceptable range is that it should fulfill 5 to 10% of our energy needs. For a 2,000-calorie diet, this means 100 to 200 calories of energy coming from linoleic acid, or about 11 to 22 grams of the fatty acid. More than that and we could invite bad health outcomes, although the evidence there is still very much debatable.
This century-long increase in our consumption of linoleic acid may be taking a turn, though. Many seed oils are now modified to reduce their linoleic acid content and instead contain more oleic acid, which is an omega-9 monounsaturated fatty acid. High-oleic sunflower oil, for instance, also has the advantage of beingĚý, as oleic acid doesn’t oxidize as easily as linoleic acid. As these oils become more widespread, the population’s consumption of linoleic acid will decrease.
As if this story wasn’t complicated enough, it’s worth mentioning the existence ofĚýĚýor CLA, which is a biohydrogenated form of linoleic acid. This modification happens naturally in ruminants, like cows and sheep, but it can also be achieved in the laboratory. It is generally regarded as safe and may not have the same health impact as linoleic acid itself. The studies so far offer mixed results.
On the topic of linoleic acid, more and better studies are definitely needed to fully assess its health impact and help determine the optimal amount we should be getting from our diet. As I delved into the research literature, I couldn’t help but notice a number of studies and review articles with financial ties to the food industry: aĚýĚýwho received support from the California Walnut Commission; aĚýĚýin charge of a non-profit funded by 19 different food and beverage companies; and aĚýĚýorganized and financed by a branch of the Danone multinational corporation. The influence of the food industry on research into food itself is understandable, but it does add a layer of potential bias.
If all this nuance is too much for your brain to handle—and believe me, on some days, it can give me a headache—you can always turn to people like Joe Mercola who offer a black-and-white version of the world that is at once simple and wrong. His big revelation over the supposed dangers of linoleic acid came fromĚý. That’s right. A guy who studied history and pre-law and who became an asset manager cut out seed oils from his diet, and his inflammatory bowel disease apparently improved dramatically within 48 hours. This non-expert had the hubris to tell Mercola, “What nobody’s really done is connect all the dots.” (Mercola even managed to squeeze out aĚýĚýabout his loathing of linoleic acidĚý)
It's easy to become lost in the online finger-pointing over which culinary culprit deserves to be kicked out of our diet this year. The truth is that diet is complex and detailed recommendations will not fit everyone. That’s why you should consult with a registered dietitian if you have questions about what you ought to eat. The bottom line is that linoleic acid is essential to our health, though we should keep an eye on our consumption so that we don’t overdo it, just in case.
“Everything in moderation” is still a pretty decent compass when navigating the fear-infested waters of the nutrition world.
Take-home message:
- Linoleic acid is an omega-6 fatty acid found in nuts and in vegetable oils, and our consumption has increased dramatically in the last 100 years in the WestĚý
- There is good evidence that linoleic acid does not cause chronic inflammation and that it is good for the health of our heart and blood vessels
- The full impact of linoleic acid on our health is not yet known, and while scientists can’t agree on what the optimal amount should be in our diet, a common recommendation is 100 to 200 calories from linoleic acid in a 2,000-calorie diet, which is in keeping with the average consumption in the United States
