Cooking oils used in ultra-processed diets may be causing a surge in colon cancer cases, a new US government-led study has shown. Unhealthy seed oils like sunflower, grapeseed, canola, and corn could trigger chronic inflammation in the body, the groundbreaking research found.
Until now evidence linking cooking oil to colon cancer has been inconclusive.
But the recent study identified seed oils as the possible contributing factor when they examined tumours from more than 80 people with colon cancer, aged between 30 and 85.
The tumours showed increased levels of bioactive lipids, which are small oily molecules produced when the body metabolises seed oils, compared to healthier fats, according to the study published in the Gut journal.
As well as increasing inflammation, bioactive lipids hinder the body’s natural healing process and foster tumour growth.
Oils rich in omega-3 fatty acids, found in avocados and olives, are a healthier alternative, the researchers said.
Seed oils contain omega-6 and polyunsaturated fatty acids whereas olive and avocado oil have good fats like omega-3. Although America’s main cancer bodies say that there is no evidence moderate seed oil consumption contributes, there has been increased research into inflammation in the body and conditions like diabetes and heart disease.
The study published in the medical journal Gut looked at 81 tumour samples in people aged between 30 to 85 and found that they had significantly higher levels of the lipids caused by seed oils than healthier fats in their cancerous tumours. This suggests the compounds in the oils are being absorbed into the body and into cancers.
Renowned physician-scientist Dr. Timothy Yeatman said the findings stressed an urgent need to reevaluate parts of the Western diet, including added sugars, saturated fats, ultra-processed foods, chemicals and inflammatory seed oils.
“It is well known that patients with unhealthy diets have increased inflammation in their bodies,” said Dr. Yeatman, who is also an associate centre director for Translational Research and Innovation at the TGH Cancer Institute.
“We now see this inflammation in the colon tumours themselves, and cancer is like a chronic wound that won’t heal – if your body is living off of daily ultra-processed 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.”
But top US health institutions have clarified that consuming moderate amounts of seed oils as part of a balanced diet has not been shown to cause cancer.
Robert F Kennedy Jr., Donald Trump’s pick to head the US Health and Human Services Department, wrote on X that Americans are being unknowingly poisoned by seed oils. He joins a growing list of people claiming that these oils are toxic.
Raysa El Zein, Lecturer in Life Sciences, University of Westminster, told The Conversation : “Seed oils include sunflower, rapeseed, corn and grapeseed oils. High heat, chemical solvents and extreme pressure are used to extract the oil from plant seeds. They are then further refined to stabilise it.
“These refining processes can affect the chemical compounds of the oil, reducing the amount of healthy antioxidants, polyphenols and phospholipids. However, this process gives the oil a longer shelf life and stabilises the oil so that it doesn’t burn at high temperatures.
“Many social media influencers claim that seed oils contain toxins. But most of these compounds, such as pollutants and heavy metals, are removed during refining. The amount that is left is too small to cause humans any harm.
“The main issue with these oils is that some fast-food outlets reuse them to cut costs. Once reused and reheated, trans fats, which increase “bad cholesterol” and decrease “good cholesterol”, can form in the oil. However, most health and safety regulations ban the reuse of oils in food establishments.
“Most seed oils are rich sources of omega-6 fatty acids. According to decades of rigorous research, these unsaturated fatty acids have many health benefits. They are linked to reduce risk of heart disease and improvements in cholesterol levels.”
She added: “Omega-6 can increase the risk of inflammation throughout the body. Inflammation is linked to many chronic diseases, including heart disease and diabetes. Studies show that omega-6 intake should be limited and tempered by consuming omega-3 fatty acids, which are anti-inflammatory.
“A healthy diet should ideally have an omega-6 to omega-3 ratio of four to one (4:1). A diet with omega-3 can help control the harms of overconsumption of omega-6 from seed oils. However, different ratios of omega-6 to omega-3 fatty acids can help reduce the risk of certain chronic diseases. For example, a ratio of 5:1 may be beneficial for people with asthma. And ratios of 2:1 to 3:1 have been shown to reduce inflammation in people with rheumatoid arthritis.”
Raysa said: “As long as people consume enough omega-3, the consumption of omega-6 would not cause inflammation. In fact, their combined intake would reduce the risk of several chronic diseases, such as heart disease and diabetes.
“While seed oils are not toxic, fat intake should be moderated in any diet to maintain good health. Fat intake is essential as it helps with the absorption of fat-soluble vitamins (vitamins A, D, E and K), the deficiency of which can have dire consequences for your health.
“A diet with some seed oil will not cause ill health. Seed oils also do not cause obesity, as some people are claiming. Obesity is linked to multiple factors beyond the type of oil being consumed. There is a stronger association between obesity and the amount rather than the type of oil consumed.
“The main issue with seed oils is that they are mostly found in highly processed food and fast food. Reducing the intake of ultra-processed food, whether made with seed oils or not, would have more health benefits than simply cutting down on seed oil. A lot of these foods are high in refined sugar, trans fats and salt, which do more damage to health than seed oils.
“Evidence shows that seed oils are a healthier alternative to animal fats. Decades of evidence show a clear link between the replacement of animal fat with plant-based oils with a reduced risk of heart disease.
“For people cooking at home, a bit of oil, whether seed or fruit oil, will not damage your health. Used in moderation and as part of a varied, whole-foods-based diet, seed oils can be a valuable addition to a healthy lifestyle. As with all foods, moderation is key.”
In a new study published this week, doctors warned that eating large amounts of seed oils such as sunflower, grapeseed, rapeseed and corn could increase the risk of bowel cancer.
Some oils used in cooking could be driving a surge in young people developing bowel cancer, according to a new study. Rates of bowel cancer in young people are rising more sharply in England than in many other countries around the world.
Early onset bowel cancer in those aged 25 to 49 is increasing globally, but England is among the countries with the biggest rise, averaging a 3.6% increase every year, researchers calculated. Studies are ongoing to work out why more younger people are developing bowel cancer, but experts believe poor diet, more ultra-processed foods, obesity and a lack of exercise are playing a role.
The study, published in the journal Lancet Oncology, found bowel cancer rates in young people rose in 27 out of the 50 countries studied in the decade to 2017. Researchers from the American Cancer Society, who led the findings, said the rise in early onset cancers is no longer limited to high-income Western countries but is now a “global phenomenon”.
They added: “The rise in colorectal cancer was confined to the younger age group (25-49 years) in 14, primarily high-income, Western countries (Australia, Canada, France, Germany, Ireland, New Zealand, Norway, Slovenia, England, Scotland, and the USA), and also in Argentina, Israel, and Puerto Rico.”
Young women were found to have faster increases in early bowel cancer rates than men if they lived in England, Norway, Australia, Turkey, Costa Rica and Scotland.
Dr Hyuna Sung, senior principal scientist at the American Cancer Society, said: “The global scope of this concerning trend highlights the need for innovative tools to prevent and control cancers linked to dietary habits, physical inactivity, and excess body weight.
“Raising awareness of the trend and the distinct symptoms of early-onset colorectal cancer (eg rectal bleeding, abdominal pain, altered bowel habits, and unexplained weight loss) among young people and primary care providers can help reduce delays in diagnosis and decrease mortality.”
Jon Shelton, head of cancer intelligence at Cancer Research UK, said: “We know that risk factors like diet, obesity, alcohol and smoking could be explanations for the rising incidence of early-onset bowel cancer in different demographics. Improvements to detection meaning that people are diagnosed at a younger age could also be playing a key role in higher rates.”
Data provided by the charity up to 2019 suggests bowel cancer has seen a 52% increase in incidence rates for adults aged 25 to 49 since the early 1990s. There are around 2,600 new bowel cancer cases in people aged 25-49 in the UK every year and around 44,100 new cases among all ages.
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