For decades, the number one dietary evil in America has been saturated fat (sat fat). Ask most doctors and nutrition experts the one thing you should remove from your diet over everything else, and you are likely to be told that red meat, butter and other sources of sat fat must go. The diet dictocrats have suggested that you should substitute omega-6 PUFAs (polyunsaturated fatty acids) for sat fats. They recommend corn, sunflower, soybean, canola and safflower oils, among several others. Intake of such oils has increased dramatically in recent decades. A new study from the University of South Florida (Gut, December 10, 2024) suggests that vegetable oils rich in omega-6 fatty acids may contribute to gut inflammation and colon cancer.
Our Love Affair with PUFA Vegetable Oils:
One of the gurus of the nutrition world is Dariush Mozaffarian, M.D., Dr.P.H. He is a cardiologist and Director of the Tufts Food is Medicine Institute at the Friedman School of Nutrition Science and Policy at Tufts University. Prior to that he was on the faculty of the Harvard School of Public Health where he founded the school’s program in Cardiovascular Epidemiology. Dr. Mozaffarian has authored more than 500 publications. Many of them had to do with nutrition. He is what most people would call a heavy hitter in the field of nutrition.
On August 20, 2019 he was quoted in a Harvard Health publication titled “No Need to Avoid Healthy Omega-6 Fats.”
The article poses some doubt about the health benefits of omega-6 polyunsaturated fats:
“The main charge against omega-6 fats is that the body can convert the most common one, linolenic acid, into another fatty acid called arachidonic acid, and arachidonic acid is a building block for molecules that can promote inflammation, blood clotting, and the constriction of blood vessels. But the body also converts arachidonic acid into molecules that calm inflammation and fight blood clots.
“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.”
Dr. Mozaffarian dismisses any concern about omega-6 fatty acids:
“Omega-6 fats are not only safe but they are also beneficial for the heart and circulation.”
People Bought the Message That PUFA Vegetable Oils Are Healthy:
As mentioned, consumption of vegetable oils like sunflower, corn, soybean and safflower oils has soared. People believed that the most important goal to good health was to lower blood cholesterol, which has long been thought to be the main culprit behind heart disease.
PUFAs are found in vegetable oils, so tens of millions of Americans followed decades of dietary recommendations. They stopped cooking with butter. Many also shunned olive oil because it contained some saturated fats and was low in PUFAs. Because saturated fat was so vilified, people switched to “light” oils and nutritionists patted them on the back.
Fast Forward to December 10, 2024–PUFAs and Colon Cancer:
The research paper in the journal Gut (Dec. 10, 2024) has shaken the nutrition experts to their core. That’s because the headlines have been hard on omega-6 PUFA vegetable oils:
- “Are Your Cooking Oils Increasing Cancer Risk? Doctors Raise Alarming Concerns” — The Economic Times, Dec. 11, 2024
- “Common Cooking Oil Could Be Causing Colon Cancer Surge in Young People, Warn Doctors” — Independent, Dec. 12, 2024
- “Cancer Warning Issued Over Popular Cooking Oil That is ‘Poisoning’ Americans” — The Mirror, US, Dec. 11, 2024
Such headlines are clearly designed to grab eyeballs. But is there any truth to these scary stories? You would have to read the article in the highly respected journal Gut to understand what is going on. And it is pretty technical.
The investigators are from the the University of South Florida and Tampa General Hospital. The point of the study was to use very sophisticated technology to detect how vegetable oils from seeds might cause chronic inflammation and cancerous cell changes. They also flagged ultra-processed foods that frequently contain inflammatory seed oils.
Here is how the corresponding author of the research describes the importance of this study:
“’It is well known that patients with unhealthy diets have increased inflammation in their bodies,’ said Dr. Timothy Yeatman, professor of surgery in the USF Health Morsani College of Medicine and associate center director for Translational Research and Innovation at the TGH Cancer Institute. ‘We now see this inflammation in the colon tumors themselves, and cancer is like a chronic wound that won’t heal – if your body is living off of daily ultraprocessed foods, its ability to heal that wound decreases due to the inflammation and suppression of the immune system that ultimately allows the cancer to grow.’”
“According to Yeatman, this study emphasizes the urgent need to reevaluate the components of the Western diet, which typically consists of excessive consumption of added sugars, saturated fats, ultra-processed foods, chemicals and inflammatory seed oils. In previous studies, the USF Health Heart Institute found an imbalanced diet not only impacts colorectal cancer, but also plays a role in other diseases, including Alzheimer’s, diabetes and cardiovascular conditions.”
The alternative healthy fats are omega-3 fatty acids found in olive oil and fish. Avocados and avocado oil are also high in omega 3s. Dr. Yeatman goes on to state:
“This has the potential to revolutionize cancer treatment, moving beyond drugs to harness natural healing processes. It’s a vital step toward addressing chronic inflammation and preventing diseases before they start.”
The Sydney Diet Heart Study Confounded Researchers:
Please step into my time machine and travel to Sydney Australia several decades ago. Between 1966 and 1973, a randomized controlled trial called The Sydney Diet Heart Study (SDHS) was carried out in Australia. This is gold-standard research that trumps the usual epidemiological studies that simply look to see what people are eating on their own and how they fare.
In this study, 458 men who had recently had a “coronary event” (a heart attack or something like it) were randomly assigned to two separate dietary groups. One group was told to carry on its usual way of eating, with the expectation that it would be using the butter and ordinary margarine that was common in Australia at that time.
The other group got safflower oil and margarine made from safflower oil rich in omega 6 linoleic acid. This is the most common of the PUFAs that Americans as well as Australians consume. Back in 1978 when the study results were first published, there was no analysis of which men had more heart attacks and heart attack deaths.
Scientists recently recovered the original data, dusted them off and analyzed them (BMJ, online, Feb. 5, 2013). The results were alarming. The men who had been provided with “heart-healthy” safflower oil were 60% more likely to die during the study (17.6% of them died compared to 11.8% of the men on their usual unsupervised diets). In addition, they were 75% more likely to die of coronary heart disease (16.3% of the men on the PUFA-rich diet compared to 10.1% of the men eating butter).
Even though the men consuming omega-6 PUFAs did lower their cholesterol as the investigators had hoped, this did not save their lives. Switching to a diet rich in linoleic acid was counterproductive for preventing heart disease and cardiac mortality.
Here, in their own words, are the conclusions of the Australian researchers:
“In this evaluation of data from the SDHS [The Sydney Diet Heart Study], selectively increasing the n-6 PUFA LA [omega-6 polyunsaturated fatty acid linoleic acid] from safflower oil and safflower polyunsaturated margarine increased rates of death from cardiovascular disease, coronary heart disease, and all cause mortality compared with a control diet rich in SFA [saturated fatty acids] from animal fats and common margarines. This is the first published report to show an increase in mortality from cardiovascular disease and coronary heart disease, comparing this LA [linoleic acid] intervention to the control group, and demonstrating that the magnitude of increased n-6 LA intake was associated with higher risk of death.”
These results throw the traditional diet-heart hypothesis into question and suggest that overdoing on omega-6 fatty acids in the diet might not be a good idea. In fact, it might be a bad idea! And this is not the first time vegetable oils high in omega-6 fatty acids have been called into question.
The Australian investigators point out that:
“These unfavorable effects of n-6 LA shown in the SDHS are consistent with two other randomized controlled trials, in which experimental dietary conditions selectively increased n-6 LA in the place of SFAs by replacing animal fats and common margarines with corn oil. Together, these three trials provide a rare opportunity to evaluate the specific effects of increasing n-6 LA without confounding from concurrent increases in n-3 PUFAs. In a pooled analysis, the increased risks of death from coronary heart disease (hazard ratio 1.33 and cardiovascular disease (1.27) approached significance. Secondary prevention trials showed significant adverse effects of n-6 LA on coronary heart disease mortality (1.84). By contrast, pooled analysis of the four randomized controlled trials that increased n-3 PUFAs alongside n-6 LA showed reduced cardiovascular mortality (0.79).”
What that means in plain English is that using vegetable oils high in omega-6 fatty acids increased the risk of death from heart disease whereas using omega-3 fatty acids actually reduced cardiovascular mortality. Our ancestors ate meat that was raised on grass rather than corn. That food was high in omega-3 fatty acids. And people who ate a Mediterranean diet also consumed foods high in omega-3 fatty acids. Olive oil is a prime example of a heart-healthy oil.
So there you have it. The diet dictocrats have been telling people to use PUFAs like safflower and corn oil because they are supposed to be “heart healthy.” Turns out they were wrong. And according to the Australian researchers, this is especially true for people who smoke or drink, exposing their bodies to excessive oxidative stress. When breakdown products of linoleic acid are oxidized, they form nasty compounds that are likely to cause clogging of coronary arteries. Nutrition scientists now urge caution in simply substituting omega-6 PUFAs for sat fat around the world.
Learn More:
Once again we have learned a painful lesson. The “experts” don’t always know what is best for us. It can take decades to unscramble dietary dogma and learn that grandma’s wisdom was right after all.
To learn more about heart-healthy food and the specifics of the Mediterranean diet we suggest our book, The People’s Pharmacy Quick & Handy Home Remedies. It is loaded with common sense solutions to common problems and details about heart healthy food. If you have ever wondered about how to follow a Mediterranean diet, you’ll get good tips here.
If you are having a hard time swallowing this new information, we encourage you to check out the research in the BMJ for yourself. Because it does not fit with the prevailing paradigm, it is likely to sink without a trace. But when you read the original research you will see that evidence trumps long-held dietary dogma.
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