Misleading: Processed foods, which are rich in sugar, fat, and salt, also tend to contain seed oils. The health risks from eating processed food are primarily related to their high caloric and salt content. Seed oils aren’t intrinsically harmful and can even be beneficial for health when taken in moderation.
FULL CLAIM: “Doctors warn cooking oil used by millions may be fueling explosion of colon cancers in young people”
On 10 December 2024, the Daily Mail published an article bearing the headline “Doctors warn cooking oil used by millions may be fueling explosion of colon cancers in young people”. More specifically, the type of cooking oil referred to in the article was seed oils. Seed oils, also known as vegetable oils, are produced from processing whole seeds, like sunflower, flax, and sesame seeds.
This claim was based on a study by Soundararajan et al. published in the journal Gut in December 2024[1].
Social media posts by various wellness influencers brought the Mail’s headline to millions of users. Among these were Instagram posts by entrepreneur Dave Asprey, who has promoted the scientifically questionable Bulletproof Diet, and physician Leigh Erin Connealy, who was reprimanded by the Medical Board of California for unprofessional conduct in 2017.
These posts are part of a popular trend on social media claiming that seed oils are harmful to human health. A 2022 article by Rolling Stone documented the rise of this trend, facilitated by wellness influencers. More recently, Robert F. Kennedy Jr., who has been nominated by U.S. President-elect Trump to lead the U.S. Department for Health and Human Services, claimed in October 2024 that Americans are being “unknowingly poisoned” by seed oils.
This trend might have its roots in health misinformation about canola oil (a seed oil), which started circulating years ago via chain emails, as this 2017 fact-check by Snopes can attest to. Misinformation specifically about canola oil has continued to circulate in recent years, this time on social media, as documented by fact-checking groups at Lead Stories and USA Today.
Like these earlier instances of canola oil misinformation, the Mail headline is misleading and the study it cited doesn’t provide sufficient evidence to support its claims. We explain more below.
What did the study do and what did it find?
The study in question analyzed lipid content in colon tumor tissue from colon cancer patients and normal colon tissue from healthy people, using a technique called mass spectrometry. It also analyzed the expression of genes involved in lipid metabolism. The authors observed that compared to normal colon tissue, tumor cells contained more lipids and gene expression activity associated with promoting inflammation.
More specifically, these pro-inflammatory lipids were derived from arachidonic acid, an omega-6 fatty acid. And arachidonic acid in turn is derived from linoleic acid, another omega-6 fatty acid present in our diet, such as seed oils. Both linoleic acid and arachidonic acid are essential fatty acids, meaning that our body cannot synthesize them, so we need to obtain them through our diet.
The greater levels of arachidonic acid-derived lipids led the authors to hypothesize that consuming a large quantity of linoleic acid in the long run, such as through seed oils, could promote chronic inflammation in the colon, thus increasing the risk of colon cancer.
The authors also hypothesized that shifting lipids and gene expression activity towards reducing inflammation could help treat colon cancer. However, neither of these hypotheses were actually tested in the study, with the authors stating that these could be potential avenues for future research.
We reached out to the study’s corresponding author, Timothy Yeatman, a professor of surgery at the University of South Florida. In an email, Yeatman stated that they “did not measure the effects of seed oils or cooking with seed oils directly on patients”.
But he postulated that since omega-6 fatty acids can only be derived from food, “eating large quantities of omega-6 lipids over the course of years and even decades may result in chronic inflammation” that could contribute to cancer development.
Since seed oils are rich in omega-6 fatty acids and are widely used in processed food in the Western diet, “we hypothesize that their substantial over-abundance in the diet is problematic,” Yeatman said.
The study isn’t equipped to show that seed oils cause colon cancer
There are a variety of known risk factors associated with an increased risk of colon cancer, including a diet high in red meat, smoking, and advanced age. Researchers continue to explore other potential contributing factors to colon cancer risk.
The Gut study shed light on the differences in lipid metabolism between colon tumor tissue and normal colon tissue. But the Mail’s headline is misleading because the study wasn’t equipped to establish a causal relationship between seed oils and the rising incidence of colon cancer in young adults.
Firstly, the average age of the participants in the study was 64 years old. This means its study population didn’t represent young adults.
Secondly, the study didn’t collect information about participants’ diets. As such, it’s impossible to establish a causal relationship between dietary seed oils and colon cancer. Moreover, omega-6 fatty acids aren’t only present in seed oils. Fish, meat, and eggs also contain omega-6 fatty acids like linoleic acid. In order to establish a causal relationship between seed oils and colon cancer specifically, we’d need to have more granular data about participants’ diets.
Thirdly, cancer typically develops over the course of years, not overnight. Colon tissue samples tested in the study were taken at a single point in time, and so may not be representative of the conditions in the colon during the participant’s lifetime.
Seed oils aren’t inherently harmful and can even be beneficial when taken in moderation
This article from Massachusetts General Hospital highlighted that seed oils have gotten a bad rap for allegedly promoting inflammation due to their linoleic acid content. As explained earlier, linoleic acid is converted to arachidonic acid in the body, and arachidonic acid is a component for compounds in the body that promote inflammation.
However, this criticism is misguided, because arachidonic acid is also a building block for compounds that reduce inflammation.
The Linus Pauling Institute at Oregon State University also stated “it is an oversimplification” to call all lipid mediators derived from arachidonic acid as “pro-inflammatory”. It added that while arachidonic acid-derived prostaglandins do induce inflammation, they also inhibit pro-inflammatory signaling molecules like leukotrienes and induce anti-inflammatory compounds called lipoxins.
Furthermore, framing linoleic acid and arachidonic acid solely as harmful is incorrect and overlooks the critical functions they play in the human body. Arachidonic acid forms part of the cell membrane’s phospholipid bilayer, which contributes to membrane fluidity and permeability. It’s also important for making lipid compounds in the body that are important for cellular processes.
Finally, there are studies indicating that dietary linoleic acid isn’t necessarily associated with more inflammation and harm. A review that looked at 30 randomized clinical trials found that dietary linoleic acid wasn’t associated with a higher level of inflammatory markers in the body[2].
In fact, a review in the journal Circulation found that dietary omega-6 fatty acids were associated with a reduced risk of cardiovascular diseases[3]. This is likely due, at least in part, to the fact that omega-6 fatty acids are unsaturated fats, or “healthy fats”, which help maintain healthy cholesterol levels. This is in contrast to saturated fats found in animal fat like butter and beef tallow, which increase the amount of “bad cholesterol” in the body.
The criticism of seed oils may be due to their use as a common ingredient in processed and ultra-processed foods. But experts have pointed out that blaming only seed oils for health problems related to processed food is misguided. While it’s true that processed food, like fried foods, contain seed oils, they also contain a high amount of refined sugar, fat, and sodium. Rather than focus specifically on seed oils, they recommend for people to generally reduce their consumption of processed food and increase their intake of fresh food.
Conclusion
In conclusion, the study by Soundararajan et al. found that colon tumor tissue contained more pro-inflammatory lipids compared to normal colon tissue. It also found that these lipids were primarily derived from omega-6 fatty acids, specifically arachidonic acid. This led the researchers to hypothesize that excess consumption of omega-6 fatty acids could increase the level of pro-inflammatory lipids in the body, leading to chronic inflammation in the colon and contributing to cancer development.
However, the study didn’t examine seed oils specifically or the effects of seed oils in colon cancer patients, and the study population was significantly older, meaning it wasn’t representative of young adults. Therefore, the Mail’s claim that the study suggests seed oils are causing an “explosion” of colon cancer in young adults is misleading and exaggerates the findings of the study.
REFERENCES
- 1 – Soundararajan et al. (2024) Integration of lipidomics with targeted, single cell, and spatial transcriptomics defines an unresolved pro-inflammatory state in colon cancer. Gut.
- 2 – Su et al. (2017) Dietary linoleic acid intake and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials. Food and Function.
- 3 – Harris et al. (2009) Omega-6 Fatty Acids and Risk for Cardiovascular Disease: A Science Advisory From the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation.
