It is possible that the healthy fats we’re told to eat to prevent heart disease are actually causing heart problems?
Dr. James DiNicolantonio, Doctor of Pharmacy and a cardiovascular research scientist, regularly presents information on the association between Omega-6 fatty acids and cardiovascular disease.
Dr. DiNicolantonio did so in March 2022 at a the Future of Fat Summit, sponsored by Zero Acre Farms. (Zero Acre intends to announce an alternative to seed oils in the near future with help from investors. This information is not an endorsement of Zero Farms, or any seed oil alternative. However, the Future of Fat Summit does offer a digestible (ha!) format, presenting some of the crucial problems with the seed oil industry, and we might as well dig in especially if you’re wanting to avoid pain and inflammation.)
This article is a summary and breakdown of the potential relationship between Omega-6 polyunsaturated fatty acids and the increased risk of heart problems as found in that presentation.
- the difference between various kind of omega fatty acids (Omega-3,6,9);
- a potential mechanism for why certain oils may impact the heart in a negative way;
- and some of the controversial history of some of the clinical research on the heart and seed oils
While the whole world is in a big argument over whether a low-fat or low-carb diet is better for weight loss (and by association the heart), there is a smaller less known debate about whether certain kinds of long fatty acids (polyunsaturated fats) contribute to heart disease.
As a participant in the Future of Fat Summit, and based on the body of his published work, Dr. DiNicolantonio is at odds with several conventional notions of what is good for the body. His review of the research on salt, saturated fat, and fatty acids are just a few examples. His presentation on certain Omega-6 fatty acids and their potential relationship to heart disease is extremely eye-opening if the correlation turns out to be true.
What is your cardiologist’s view of Omega-6 seed oils?
The current conventional view of the relationship between Omega-6 seed oils and heart disease is that most Omega-6 fatty acids are a form of health food. The Harvard Health review provides a summary (1):
The critics argue that we should cut back on our intake of omega-6 fats to improve the ratio of omega-3 to omega-6s. Hogwash, says the American Heart Association (AHA). In a science advisory that was two years in the making, nine independent researchers from around the country, including three from Harvard, say that data from dozens of studies support the cardiovascular benefits of eating omega-6 fats (Circulation, Feb. 17, 2009). “Omega-6 fats are not only safe but they are also beneficial for the heart and circulation,” says advisory coauthor Dr. Dariush Mozaffarian, an assistant professor of medicine at Harvard-affiliated Brigham and Women’s Hospital.Harvard Health Publishing – No Need to Avoid Healthy Omega-6 fats (August 20, 2019)
There may be low quality Omega-6 fats, according to Harvard, but the conventional view is not buying the idea that some Omega-6s are ultimately bad for the cardiovascular system. Why?
It turns out that the body converts very little linolenic acid into arachidonic acid, even when linolenic acid is abundant in the diet. The AHA reviewers found that eating more omega-6 fats didn’t rev up inflammation. Instead, eating more omega-6 fats either reduced markers of inflammation or left them unchanged. Many studies showed that rates of heart disease went down as consumption of omega-6 fats went up. And a meta-analysis of six randomized trials found that replacing saturated fat with omega-6 fats reduced the risk of heart attacks and other coronary events by 24%. A separate report published in the American Journal of Clinical Nutrition that pooled the results of 11 large cohorts showed that replacing saturated fats with polyunsaturated fats (including omega-6 and omega-3 fats) reduced heart disease rates more than did replacing them with monounsaturated fats or carbohydrates.Harvard Health Publishing – No Need to Avoid Healthy Omega-6 fats (August 20, 2019)
Linolenic acid and Omega-6 fats or fatty acids mean the same thing in the above paragraph (it looks like the Harvard site probably meant Linoleic acid); in short, the conventional evidence is that the decrease in the signs of cardiovascular disease by adding Omega-6s to replace saturated fat is just too strong to question the possibility of some Omega-6s being unhealthy.
Therefore in its list of healthy oils Harvard (and other conventional sources) will list corn oil, soybean oil, and sunflower oil. And while not listing liquid vegetable oil as a healthy oil, the health by association is potentially implied. The conventional view may go so far as to suggest heart patients increase their sources of Omega-3 fats (to improve the Omega-3 to Omega-6 ratio) while not worrying about reducing Omega-6s.
So what’s going on? Is there a way to reconcile the conventional view with the information presented by seed oil skeptics?
What do we mean by Omega-6s? It’s going to get confusing for a minute
Linoleic acids, Omega-6 polyunsaturated acids (PUFAs), Omega-6 fatty acids, Omega-6 fats, Omega-6 long chain fats or fatty acids, all mean the same thing. They are all synonyms for Omega-6s, most of the time. There are other forms of Omega-6 in the human diet besides Linoleic acids, however most people will get a majority of their Omega-6s from food sources with linoleic acids.
Fatty acids whether they are saturated or unsaturated, start with a Carboxylic Acid molecule, followed by a chain of carbons. This acid group is what makes them a form of “acids” in the body. (Amino acids also start with the same group.)
If those chains of carbons fully are loaded with hydrogens, they are called saturated. If those chains are not fully loaded with hydgrogens, they are called unsaturated.
There are two kinds of unsaturated oils, monounsaturated and polyunsaturated. Omega-6s are polyunsaturated. Polyunsaturated (PUFA) means that their long, chain-like structure has more than one double bond. Monounsaturated (MUFA) only has one double bond. Soybean oil is an example of a polyunsaturated oil and avocado is an example of a monunsaturated oil.
soybean oil shows that these terms are difficult to keep separate
Now that we kind of have a handle on this, let’s take a look at soybean oil, and confuse the situation. On one hand soybean oil is an Omega-6 linoleic acid. But one the other hand, is also contains some small amounts of alpha-linolenic acid or ALA (read carefully: linolenic vs. linoleic). So the majority of most soybean oils will be made of Omega-6s, but there will also be some small amount of Omega-3s, and an even larger amount of monounsaturated fatty acids as well.
How is this possible? Because soybean oil is actually a mix of several different similarly shaped fatty acids, some of which have different bonding patterns, even though it is most known for being a Omega-6 linoleic.
it gets worse: some authorities don’t specify which fatty acids they mean
Omega-3 or Omega-6? Linoleic or Linolenic? What about the monounsaturated part of the oil? When it comes to a particular vegetable oil (let’s say corn or soybean) that is made up of a combination of all of these kinds of fatty acids, which part are we talking about?
Both the vegetable oil enthusiasts and vegetable oil critics often aren’t always very clear on which part of the oil they mean when they discuss the general evidence for healthy or non-healthy inflammation and this can get really, really confusing for the casual reader who may not understand the difference.
Omega-3 vs Omega-6 vs Omega-9, rules for keeping the names straight?
Here’s some help to keep the fatty acid story straight in your brain. Almost every single vegetable oil has variety of concentrations of Omega-3 and Omega-6 polyunsaturated acids, and even monounsaturated acids. Some examples will be provided down below (2).
omega-3 fatty acids from plants are alpha-linolenic (ala)
Omega-3 fatty acids are a group of fatty acids called ALA, EPA, and DHA. For simplicity sake, when people talk about supplementing with Omega-3s, they’re looking for a combination of all three. For this article, we’re talking specifically about ALA – which is Alpha-Linolenic acid.
ALAs are found exclusively in seeds, nuts, and vegetable oils. Fish oils and are a known source of EPA and DHA, but not ALA. So when people talk about getting Omega-3s from plants, they’re talking about ALA or linolenic acid.
All Omega-3s are essential fatty acids which means we need them for normal biological processes, but cannot make them. So it’s common for authorities to talk about seed and vegetable oils while referring to the health benefits of Omega-3, and therefore also refer to seeds, nut, and vegetable oils as a health food.
Most of the highly consumed seed oils, including soybean oil and corn oil, have a small amount of ALA (Omega-3) present in their makeup.
omega-6 fatty acids are linoleic acids
With their double-bonds in different positions than the Omega-3s, many vegetable oils are predominantly Omega-6 fatty acids, or linoleic acids. The concern of seed oil critics is the role of linoleic acids, not linolenic acids.
Just like Omega-3s, linoleic acids are essential fatty acids, which means we need to consume them because we cannot make them. There is no discussion of removing all linoleic PUFAs from the diet as that would be impossible. The traditional question is if there’s a difference in the source of Omega-6s, their ratio to Omega-3s, and if too many Omega-6s can lead to disease, especially if their source has a very high Omega-6 to Omega-3 ratio.
But we’re also going to explore another potential source of excessive Omega-6 as a disease source outside Omega-6 to 3 ratios.
GLA- the other omega-6 fatty acids
There is another Omega-6 acid, known as Gamma-Linolenic acids or GLAs. Note these are not known as linoleic. These fatty acids were well known to the skin and fitness industry for their use in skincare and fat loss supplement products. We’re not talking about GLA Omega-6 acids in this article.
omega-9s the monounsaturated acids (oleic)
Rarely called Omega-9s, monounsaturated acids have a single double bond in the 9th carbon position of the fatty acid chain, so they are technically Omega-9s. This article is also not particularly concerned about monounsaturated acids which are not as prevalent in the human diet as Omega-6s. That said, Omega-9s are known as oleic acids which can be confused with linoleic.
What are some examples of vegetable oils and their fatty acid ratios?
Here are some examples of commonly consumed polyunsaturated vegetable oils and the ratio of various fatty acids. The point of this breakdown is to be able to see the composition difference of certain PUFAs and why it might not be a great idea to talk about all Omega-6s as being the same.
Flaxseed oil – the “Poster Boy” for Ala Omega-3s
Out of 100 grams of flaxseed oil:
- 9 grams are saturated fatty acids
- 9 grams are monounsaturated acids (Omega-9 oleic acids )
Of the remaining 82 grams:
- 53 grams are Omega-3 polyunsaturated fatty acids (ALAs)
- 16 grams are Omega-6 polyunsaturated fatty acids (linoleic)
The other remaining grams will be various compounds like some water, some cholesterol, etc.
soybean* oil – the workhorse for “Healthy” omega-6s?
Out of 100 grams of soybean oil:
- 16 grams are saturated fatty acids
- 23 grams are monounsaturated acids (Omega-9 oleic acids)
Of the remaining 61 grams:
- 7 grams are Omega-3s polyunsaturated fatty acids (ALAs)
- 51 grams are Omega-6s polyunsaturated fatty acids (linoleic)
*This is non-hydrogenated oil, and hydrogenated soybean ratios are different, with a lower Omega-3 and Omega-6 count but with higher Omega-6 to 3 ratio
canola oil – the unicorn of omega-3 to omega-6 ratios?
Out of 100 grams of canola Oil:
- 7 grams are saturated fatty acids
- 61 grams are monounsaturated acids (Omega-9 oleic acids)
Of the remaining 31 grams:
- 9 grams are Omega-3 polyunsaturated fatty acids (ALA)
- 19 grams are Omega-6 polyunsaturated fatty acids (linoleic)
corn oil – the original golden oil
Out of 100 grams of corn oil:
- 13 grams are saturated fatty acids
- 27 grams are monounsaturated acids (Omega-9 oleic acids)
Of the remaining 60 grams:
- 1 gram is Omega-3 polyunsaturated fatty acids (ALA)
- 58 grams are Omega-6 polyunsaturated fatty acids (linoleic)
So, is a vegetable oil is a vegetable oil is a vegetable oil?
Here are some interesting takeaways from the above vegetable oil breakdowns:
- The most well known and marketed ALA Omega-3 oil flaxseed oil contains almost as many combined saturated, monounsaturated, and Omega-6 fatty acids as Omega-3s
- Soybean oil has a higher saturated fat content than other common vegetable oils, and its ratio of Omega-6 to 3 ratio is about 7:3
- Canola oil is known as a polyunsaturated oil even though the majority of the fatty acids are monounsaturated, and it has one of the lowest Omega-6 to 3 ratios, at almost 2:1
- Corn oil has the highest linoleic content, which includes an astounding 58:1 Omega-6 to 3 ratio
We can see from the hard numbers, one vegetable oil is not that the same thing as the next, even in the family of well known Omega-6 oils.
(The cooking smoke point of corn oil, canola oil, and soybean oil (non-hydrogenated) are similar at somewhere between 450 – 460 degrees Fahrenheit, which is important when we take into consideration the heating of vegetable oils as a source of oxidized lipoproteins down below.)
Why are vegetable oils seen as necessary and healthy?
Both Omega-3 ALA vegetable oils and Omega-6 linoleic vegetable oils are essential sources of two different kinds of polyunsaturated fats whose absence (though rare) can lead to disease (3).
Humans have consumed both linolenic and linoleic acids in the form of nuts and seeds (if not modern vegetable oils) for a long time, and as the above ratios attest, you cannot consume one without consuming the other.
Polyunsaturated fats are known to not raise cholesterol numbers, and since cholesterol ratios are the main plank of our current cardiovascular disease theory, replacing saturated fats with polyunsaturated fats has been the go-to strategy to prevent heart and vascular problems, without necessarily making a distinction between sources such as raw nuts and seeds and their oil counterparts.
What makes omega-6 linoleic acids essential?
Linoleic acid derivatives have roles in multiple body functions and systems. Linoleic is an essential fatty acid in that it cannot be produced by the body, but the body needs to have some source of Omega-6s for their role in the integrity of the cell membrane in many different body tissues. Here are a few examples:
- Brain function: cell membrane integrity and wound healing in brain tissue
- Skin health: wound healing and maintaining integrity of skin cell membranes
- Hair health: a metabolite of is arachidonic acid which is necessary for hair growth
- Reproduction: cell membrane integrity necessary for hormone cascade and fertilization
- Immune system: healthy immune response
- Bone health: a necessary ingredient for healthy bone mineralization
It’s clear that Omega-6s are a necessary part of the human organism according to nearly every authority. (There are some questions about how essential-ness is quantified by some nutritional experts, but that is beyond the scope of this article.)
Can Omega-6 PUFAs cause harm in the conventional view?
It is believed that too many Omega-6s can contribute to the wrong kind of body inflammation (i.e. chronic) if they are out of balance with Omega-3 fatty acids. The ideal diet would have a proper ratio of Omega-6s to Omega-3s, which is understood to give us all the benefits of linolenic acids without the unhealthy inflammation.
The rule of thumb is that an ideal diet would provide at only four grams of Omega-6s for every one gram of Omega-3s (4:1). Most estimates put the Omega-6s at four times higher than they need to be in the standard western diet. Since Omega-6s are an ingredient in most food products, it’s difficult to reduce Omega-6 consumption, and so experts simply recommend consuming more Omega-3s, like those found in fish oils.
No conventional authorities suggest reducing Omega-6 polyunsaturated oils, including seed oils
If Harvard Health and the American Heart Association are representative of the conventional view, then they say there is no reason to avoid healthy Omega-6 fats. The Harvard list for healthy Omega-6s include soybean oil, sunflower oil, corn oil, and similar vegetable oils, in addition to whole nuts and seeds. At most, conventional sources will suggest we increase our consumption of Omega-3s to maintain a healthier Omega-6 to Omega-3 ratio.
A more nuanced view comes from resources like Dr. Axe (4), which presents the data and opinion of the American Heart Association while encouraging readers to avoid genetically modified seed oils:
What is a good source of linoleic acid? The best food sources include organic, non-GMO vegetable oils, like sunflower oil, and nuts, seeds, meat products, eggs, cheese and milk.DrAxe.com: Linoleic Acid Helps Improve Brain, Heart, Skin, Bone & Reproductive Health
While Dr. Axe won’t come out and say that most seed oils, in principle are to be avoided, he does say to avoid the GMO kind, which, if followed, would reduce most peoples’ consumption of oils like corn, soybean, and vegetable oil.
What is the arachandonic acid theory? And does it even make sense to talk about Omega-3 to 6 ratios anymore?
Where did we get the idea that linoleic acid in excess could create potential health problems? From the fact that Omega-6s acids can be converted by the body into a different kind of Omega-6 fat called arachadonic acid.
…Arachidonic acid can be converted to a myriad of bioactive compounds called eicosanoids, such as prostaglandins and leukotrienes. These eicosanoids are important in normal metabolic function of cells and tissues, but when persistently produced in excess, they are known to contribute to a number of chronic diseases, such as inflammation and cancer. It is this possible conversion to arachidonic acid for which linoleic acid has received the most notoriety.Whelan, J., & Fritsche, K. (2013). Linoleic acid.
The idea is that excessive linoleic acid leads to excess arachidonic acid, and excess inflammation. The relationship is expected to be worse if the consumption of linoleic acid (Omega-6) is proportionally in excess of linolenic (Omega-3).
Testing this theory, however, did not show the expected results.
Although it has been hypothesized that limiting the intake of linoleic acid can reduce tissue levels of arachidonic acid, this does not seem to be the case in individuals who are consuming a typical Western diet. In tracer kinetic studies, fractional conversion of linoleic acid to arachidonic acid is believed to be between 0.3% and 0.6%, and this conversion appears to be offset by turnover.Whelan, J., & Fritsche, K. (2013). Linoleic acid.
More linoleic acids didn’t lead to excessively more arachadonic acids in tissue, according to research. And some epidemiology studies couldn’t find a specific link of linoleic acids to inflammation.
The putative link between high linoleic acid intake and greater inflammation has been the subject of a recent systematic review. In this paper, the authors presented the findings from 15 randomized, controlled trials (8 parallel and 7 crossover designs) that permitted the effect of changing linoleic acid intake over a wide range to be assessed in healthy noninfant humansWhelan, J., & Fritsche, K. (2013). Linoleic acid.
This is the evidence that the American Heart Association, Harvard Health, and other conventional health sources cite in order to group a wide variety of vegetable oils with other Omega-6 containing seeds and nuts.
It makes me wonder if its even worth talking about Omega-6 to 3 ratios anymore.
What do seed oil skeptics say about the relationship between linoleic acid and heart disease?
Dr. DiNicolantonio’s presentation at the Future of Fat Summit (5) is a summary of the concerns and claims of seed oil skeptics regarding cardiovascular disease and Omega-6 fats:
- Linoleic acid is very susceptible to oxidation (light and heat create a chemical reaction that degrades the fat and creates free radicals)
- Increasing Omega-6 seed oil consumption leads to an increase in oxidized low density lipoproteins (LDL) in the body
- The presence of oxidized LDL creates cardiovascular disease including coronary artery disease
Notice that there is no mention of linoleic to arachadonic conversion, nor Omega-6 to Omega-3 ratios. The arachadonic to inflammation conversion theory is not the basis of the current concern over linoleic acids.
Instead the skeptics look at the process by which PUFAs leave the digestive system and enter the blood stream.
Can linoleic acid increase oxidized LDLs in body? A potential pathway
Most people are familiar with the idea the deep fried foods aren’t healthy due to the fact that they’re cooked in hot oil, and heated oils can break down and form unhealthy compounds. These compounds are free radicals (or peroxides) brought on by the heat and other stressors to the oil.
But all fats (corn oil, olive oil, soybean oil, etc), given enough time, will break down and oxidize, a process we describe as going rancid. The amount of time, heat, light, or other stressors it takes to create oxidation varies from oil to oil. It is the seed oil skeptic’s contention that Omega-6s PUFAs are more susceptible to oxidation than other fat sources.
Meet the chlyomicrons – how the fats we eat get used by the body
In order to be digested, fats have a different path to travel than carbs or proteins. That’s because fats are made of huge long chains of fatty acids that have have to be broken down and transported in the bloodstream before they can be integrated by the body. So how do they get from the small intestine to other tissues?
Fats have a special kind of transport called lipoproteins. They are a combination of a couple of different kind of fatty acid molecules (Triglycerides), with a cholesterol, and a protein. The makeup of the lipoprotein can be measured in its density, and humans have five different forms of lipoproteins of high and low and ultra-low density.
Chlyomicrons are low density lipoproteins that are made by the small intestine to transport the fatty acids like Omega-6s (and others) from the intestinal track to the fat stores, the heart, and other muscles.
You’re probably most familiar with the discussion of lipoproteins and density when it comes to cholesterol tests and the desire to know the balance of “good cholesterol” and “bad cholesterol.”
Does this data show that what chlyomicrons transport can lead to heart disease?
The most critical part of this criticism of seed oils is in this screenshot. It presents the outline of a mechanism by which Omega-6 PUFAs from unhealthy sources might lead to an increased risk of heart disease.
In short, linoleic acids from highly oxidized sources get taken up the lipoprotein transort (chlyomicrons) in the small intestine and taken directly to the heart where the oxidized Omega-6s brings free-radicals to the heart vessels. Dr. DiNicolantonio presents evidence from a paper (6) that reports to show direct relationship between the number of oxidized fats consumed in the meal, and the measurable oxidized fats found in the chylomicrons after the meal. Less free-radical fats, less-free radicals in the the chylomicrons and therefore, in the tissues.
The access to the paper is actually found on the American Heart Association website at the link below. The paper dates from 1994. In the experiment detailed in the paper, subjects were fed: corn oil that had not been oxidized (didn’t have many lipid peroxides); corn oil that only had some lipid oxidation; and finally corn oil that was highly oxidized.
It should be noted for this experiment that oxidation happened by leaving the oil open to air exposure for six weeks, and none of the corn oil was heated like it might be at home or in a restaurant setting.
peroxides and the American heart association
The study showed a verifiable trend between the the amount of oxidized oils in the diet and the amount of oxidized lipids found in the chlyomicrons in the bloodstream. The more oxidized the oils that were eaten, the more peroxides were found. And the presence of these peroxides were measurable for a full 8 hours after the consumption of the oxidized linoleic acids.
The above mechanism is significant, then consuming highly oxidized Omega-6 acids in the form of corn oil would expose heart vessels to peroxides carried in the chlyomicrons.
hode acids lead to heart disease?
Data from another study (6) might reveal a different aspect of the chlyomicron and peroxide connection. Omega-6 linoleic acids are the most abundant fatty acids in human low density lipoproteins (chylomicrons). As stated above, as linoleic acids oxidize they form peroxides. Some of these peroxides are called HODE acids, specifically 9-HODE (short for 9-hydroxy-10,12-octadecadienoic acid).
When the bloodstreams of younger (36-47 years old) atherosclerotic patients (i.e. bad heart disease patients) and heart healthy patients are examined, the amount of 9-HODE peroxides in the atherosclerotic patients were 20 times (!) the amount of the non-atherosclerotic patients of the same age range.
When the study looked at older atherosclerotic patients (69-94 years old), the peroxide levels of 9-HODE were 30 to 100 times the amount of the young healthy subjects, but only 2-3 times higher than a non-atherosclerotic older subjects.
This led the study authors to conclude that some oxidation of fatty-acids in low density lipoprotein is natural with aging, and that oxidization is much higher in those with heart disease (atherosclerotic).
Clearly there seems to be a relationship between oxidized linoleic acids in the lipoproteins and the development of heart disease.
Are there other studies that show a relationship between Omega-6 PUFAs and worsening heart disease?
Yes, there are other studies besides the above that suggest relationship between seed oils and an increase in heart disease. Some have even been featured in recent mainstream science media.
The Sydney heart study examines large data set and finds out some Omega-6s may be harmful to the heart
The Sydney Heart Study originally was published in the 1970s, but received a new investigation in 2013 as published in the British Medical Journal (BMJ) (8). The research was conducted in the late 1960s and early 1970s on 458 men between the ages of 30 to 59 who had a recent coronary event. One group of men (about half) were instructed to replace saturated fats with a specific linoleic acid (safflower oil and safflower margarine) and the other group received no change in diet. Every other aspect about the two groups were left as similar as possible.
The study reports to be a single, blinded, randomized control trial of parallel groups.
Data on the two groups were gathered from 1966 to 1973. Both group data were analyzed for all cause mortality, cardiovascular mortality, and mortality specifically from coronary artery disease.
The intervention group replacing animal fats with linoleic acids showed increased rates of death in general, including death from cardiovascular problems, and coronary artery disease than the group that made no changes. While the increased rate was only around 6% per category in the linoleic group, it’s worth noting that any increased death rate in the seed oil group seems counter to what is reported by heart health authorities. Clearly this was not clear victory for the idea of replacing animal fats with seed oils.
As it states in the conclusion:
Advice to substitute polyunsaturated fats for saturated fats is a key component of worldwide dietary guidelines for coronary heart disease risk reduction. However, clinical benefits of the most abundant polyunsaturated fatty acid, omega 6 linoleic acid, have not been established. In this cohort, substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. An updated meta-analysis of linoleic acid intervention trials showed no evidence of cardiovascular benefit. These findings could have important implications for worldwide dietary advice to substitute omega 6 linoleic acid, or polyunsaturated fats in general, for saturated fats.Evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ, 2013
The public information cited by the American Heart Association and other conventional resources do not typically address the 2013 meta-analysis of the Sydney Heart Study in BMJ.
the minnesota coronary survey – a physician comes clean and reveals the whole story?
Imagine you find something in your basement that undermines decades of expert science advice on diet and health? What would you do ?
Author Malcom Gladwell has a podcast on this very subject from several years ago. He and his guest, a cardiologist, discuss the controversy over a study that’s now called the Minnesota Coronary Experiment; a study that seemed to reveal that seed oils high in omega-6 fatty acids aren’t really better for your heart than saturated fat, and how those results were hidden for many years…until the records were pulled out of a basement where they were sitting for years because, allegedly “We were just so disappointed in the way they [the results] turned out.”
The original presentation of the data is found in the archive of the American Heart Association Journal, Arteriosclerosis dated from 1989 more than a decade later (9). This is significant because the data was collected on over 9,000 patients in mental health facilities between 1968 and 1973, and revealed that a diet excluding animal fats and using linoleic acids did not end with better heart health. According to the Chicago Tribune, Arteriosclerosis is an obscure journal which means that the first reveal of the data did not get much attention (10).
The data received new treatment in 2016, in the BMJ (11), with a new re-evaluation, which gained some traction in the popular press due to the controversial history of the data.
The study did have one expected outcome: replacing saturated fats derived from cholesterol with a diet of linoleic acids did lower serum-cholesterol by significant amounts.
However, lowering serum-cholestrol in this manner did not show significant improvement in cardiac events. And this was in a large, double-blind, randomized clinical trial, in an institutional population whose diet could be strictly controlled and tracked. So there is not much room for scientific criticism of the data based on the standards with which institutions judge the quality of the data.
According to 2016 BMJ article:
Available evidence from randomized controlled trials shows that replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes. Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.Analysis of the Recovered Data of the Minnesota Coronary Experiment, BMJ, 2016.
In fact that results showed that for every 30 mg/dL that serum cholestrol was lowered, there was a 22% increase in risk of death. Looking at the charts provided in the original 1989 publication on all cause of death showed some potentially shocking trends for women in the treatment group who seemed to worse results than men, especially in diseases related to the brain and nervous system.
Corn oil study published in 1965 gives early indicator of problems with linoleic acids for heart disease
What has become known as “The Rose Corn Oil Study (still available in the BMJ archives), 81 heart patients under the age of 70, unlikely to have a major heart event in the next two years, were randomized to two groups (12). The experimental group was given supplementation with either olive oil or corn oil and instructed to reduce their consumption of animal derived saturated fats. The control group received the same cardiac care but did not received any oil supplementation nor dietary advice.
The trial was to last a full three years, but was cut at 2 years as over half of the participants had either had a second heart-attack or had become deceased. For the two years the study was conducted, the two groups received a physical examination every two months, which included an electrocardiogram.
By the conclusion of the trial, the group that had the fewest recurrence of heart problems was the control group (75%), who took no oil, nor received any instructions to remove saturated fats. The olive oil group was the second best performing (57%), and the corn oil group showed the worst outcome (52%), leading the authors to write:
It is concluded that under the circumstances of this trial, corn oil cannot be treated as a treatment of ischemic heart disease. It is most unlikely to be beneficial, and it is possible harmful.The Rose Corn Oil Study, 1965.
As was found in later studies, the linoleic acid group showed a decrease in serum-cholesterol over the two years in which the study was conducted. However, as was also found in the Syndey Heart Study, and the Minnesota Coronary Survey, the decrease in serum-cholesterol through the increased consumption of linoleic acids did not translated to better heart health, but did seem to show an increased risk of death.
What does it all mean? What can we say about Omega-6 PUFA and heart health?
Nothing in science is every 100%, particularly in the health sciences dealing with sources of nutrition and the body. But given the above information this is what seems likely:
- We can lower our serum-cholesterol by replacing saturated animal fats with a variety of sources of Omega-6 oils, however, there is no strong association between lowering serum-cholesterol in this way and measurable improvements in heart health
- There is an association between lowering serum-cholesterol by increasing Omega-6s from seed oils and an increased risk of death and heart disease
- There is strong evidence that increasing consumption of oxidized oils will lead to the presence of the oxidized fats (with peroxides) in the blood stream
- There appears to be a relationship between atherosclerosis (blood vessel disease) and the presence of oxidized fats in the blood stream
- Attempting to decrease the risk of atherosclerosis (and therefore heart disease) by increasing the consumption of easily oxidized oils seems like a bad way to improve heart health and overall health
- There may be a relationship, then between the increasing consumption of linoleic seed oils in food products in the past 80 or so years with the increased incidence of cardiovascular disease
What can’t we say from the above information?
- We can say that compared to replacing saturated animal fats with corn oils and other linoleic acids, not changing one’s diet after a heart event has a better outcome, however we cannot necessarily say that continuing to eat saturated animal fats is the best of all available choices (though it may be for some people)
- We can say that focusing on lower serum-cholestrol with easily oxidized linoleic fats appears to be harmful, however, we cannot necessarily say that lowering serum-cholesterol through another means will be equally as harmful
That said, if learning this kind of information increases your skepticism of certain recommendations for heart health, I would say that is understandable.
What can we say about conventional authorities and their statements on the consumption of linoleic acids?
Anyone who understands what some the clinical data says on increasing seed oils consumption has a legitimate reason to question why the increasing consumption of linoleic acids continues to be recommended by conventional authorities on cardiovascular disease, like the American Heart Association and Harvard Medical Review.
At the very least we might expect the conventional authorities to draw a distinction between linoleic acids present in the consumption of nuts and seeds and the linoleic acids present in seed oils like soybean oil, corn oil, and sunflower oil.
It’s perhaps understandable, given the depth to which linoleic acids are a part of most food products, that there maybe be pressure to downplay the potential dangers of increasing the consumption of easily oxidized Omega-6 polyunsaturated fatty acids.
In any case, anyone concerned about the development of heart disease should take serious reconsideration of their consumption of seed oils, specifically Omega-6 linoleic acids.
Anyone who wants more references or more technical exploration on the link between cardiovascular disease and linoleic acids should consider downloading and reading the DiNicolantonio/O’keefe article: Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis, in the open access journal Open Heart (13).
(1) Harvard Health Publishing. “No need to avoid healthy omega-6 fats.” August 20, 2019. https://www.health.harvard.edu/newsletter_article/no-need-to-avoid-healthy-omega-6-fats
(2) Robertson R. “Omega-3-6-9 Fatty Acids: A complete Overview.” Healthline. https://www.healthline.com/nutrition/omega-3-6-9-overview#omega-6
(3) Whelan J, Fritsche K. Linoleic acid. Adv Nutr. 2013 May 1;4(3):311-2. doi: 10.3945/an.113.003772. PMID: 23674797; PMCID: PMC3650500. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650500/
(4) Axe J. “Linoleic Acid Helps Improve Brain, Heart, Skin, Bone & Reproductive Health.” September 6, 2018. https://draxe.com/nutrition/linoleic-acid/
(5) DiNicolantonio J. “Omega-6 linoleic acid as a driver of heart disease”. Presentation: The Future of Fat Summit. March 3, 2022.
(6) Staprans I, Rapp JH, Pan X-M, Kim KY, Feingold KR. Oxidized Lipids in the Diet Are a Source of Oxidized Lipid in Chylomicrons of Human Serum. American Heart Association Journal. 1994. American Heart Association. https://www.ahajournals.org/doi/pdf/10.1161/01.ATV.14.12.1900
(7) Jira W, Spiteller G, Carson W, et al. Strong increase in hydroxy fatty acids derived from linoleic acid in human low density lipoproteins of atherosclerotic patients. Chem Phys Lipids 1998;91:1–11. https://doi.org/10.1016/S0009-3084(97)00095-9
(8) 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;346:e8707. https://doi.org/10.1136/bmj.e8707
(9) Frantz ID, Dawson EA, et al. Test effect of lipid lowering by diet on cardiovascular risk: the Minnesota Coronary Survey. Originally printed in Arteriosclerosis: 9:129-135, January/February 1989. The American Heart Association Journal. https://www.ahajournals.org/doi/pdf/10.1161/01.atv.9.1.1
(10) The Chicago Tribune. “The heretical Minnesota heart study: When science stops asking questions.” April 29, 2016. https://www.chicagotribune.com/opinion/editorials/ct-science-diet-fats-minnesota-edit-0430-jm-20160428-story.html
(11) 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;353:i1246. https://doi.org/10.1136/bmj.i1246
(12) Rose GA, Thompson WB, et al. Corn oil in the treatment of ischaemic heart disease. Br Med J. 1965 Jun 12;1(5449):1531-3. https://doi: 10.1136/bmj.1.5449.1531
(13) DiNicolantonio JJ, O’Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Heart 2018;5:e000898. doi:10.1136/openhrt-2018-000898 https://openheart.bmj.com/content/5/2/e000898.long