Beware! Seed oils in ultra-processed foods may contribute to colon cancer risk

Author: Huang Yanhong Duan Yuechu

In recent years, the incidence of colon cancer and rectal cancer in people under 50 has continued to rise. This alarming trend has worried clinicians and has also triggered an in-depth exploration of the reasons behind it by the scientific community. A study published in Scientific American on December 13, 2024, revealed a key part of this mystery.

The study, written by Lauren J. Young, analyzed colorectal cancer tumor samples from 81 people in the United States and found that these tumors contained a large amount of pro-inflammatory omega-6 fatty acids, while omega-3 fatty acids, which help suppress inflammation, were severely deficient. Inflammation is a normal defense response initiated by the human immune system to heal wounds or fight infection. But as early as the 19th century, researchers discovered that colon tumors under a microscope looked like "poorly healed wounds." Prolonged inflammation damages cells and weakens their ability to fight the growth of potential cancer cells. Timothy Yeatman, a co-author of the study and a professor of surgery at the University of South Florida, suspects that omega-6 fatty acids are likely to come mainly from ultra-processed foods. After all, many ingredients in our daily diet affect the body's inflammation levels.

Today, a lot of ultra-processed foods and fast food are cooked with seed oils. These seed oils, such as the common chemically processed vegetable oils from rapeseed, corn, grapeseed and sunflower seeds, are cheap and therefore widely used. But they contain high concentrations of omega-6 fatty acids. However, the research has not been able to conclusively link the lipids detected in colon tumors to any specific food or oil.

The importance of this research result is self-evident. At a time when the relationship between diet and health is receiving increasing attention, it has sounded the alarm for us. From a public health perspective, if the association between seed oils in ultra-processed foods and colon cancer can be further confirmed, it will have a profound impact on the production standards of the food industry and the dietary choices of consumers. For individuals, understanding these potential health risks will help us choose food more carefully, optimize our diet structure, and thus reduce the risk of disease.

Experts also expressed their own views on this research result. Andrew Chan, a gastroenterologist at Massachusetts General Hospital and professor of medicine at Harvard Medical School, who was not involved in this new study, pointed out: "Past studies have explored the relationship between dietary patterns and colorectal cancer risk. Some dietary patterns rich in pro-inflammatory oils such as omega-6 fatty acids are associated with a higher risk of cancer; while diets rich in healthy oils, such as the Mediterranean diet, seem to be associated with a lower risk. In addition, there are studies focusing on the potential role of omega-3 fatty acids (such as fish oil) in preventing colorectal cancer, but the results of related studies are inconsistent and more in-depth exploration is still needed." Chan also mentioned that factors such as genetics, exercise, lifestyle, and chemical or environmental exposure may also affect the risk of colon cancer. "The transformation and metabolism of food after entering the human body is extremely complex. How it ultimately leads to changes in lipids and other substances in tissues is still unknown. These gaps need to be further filled in order to fully explain the relationship between diet and cancer."

Yeatman further explained the relationship between lipids and inflammation: "When our hands or skin are injured, they will initially become red and swollen due to inflammation, and then recover because the inflammation subsides. Charles Serhan of Harvard University recently discovered the phenomenon of 'lipid class switching', that is, the body switches from the inflammatory stage to the resolving stage during normal healing, which is mainly guided by some omega-3 derived lipids. But if inflammation is not controlled, it may cause cancer."

Regarding how inflammation affects cancer development, Chan said: "Inflammation can cause changes in tissues that make it more difficult for cells to be replaced normally, making it easier for them to grow uncontrollably and eventually form tumors. Inflammation can also create an environment that makes the tissue's DNA more susceptible to mutations, which can lead to cancer. Inflammation may also weaken the body's natural ability to fight cancer development. Different lipids and oils may affect inflammation and normal tissue repair through specific pathways, and in some cases, this effect may promote the development of cancer due to uncontrolled cell growth in tissues."

As for why the imbalance of pro-inflammatory and pro-resolving lipids occurs, Yeatman says, “These lipids are ultimately derived from diet. Levels of omega-6 lipids (the pro-inflammatory side) in human fat have risen dramatically since the 1950s, most likely due to changes in the Western diet, with ultra-processed foods being a key factor. Not only are these lipids in ultra-processed foods, but many processed seed oils, such as soybean, canola, cottonseed, sunflower and safflower oils, are in almost all packaged foods we buy. Take bread in the supermarket, for example. Bread made by non-local bakeries often has unidentifiable ingredients such as soybean oil on the ingredient list, as well as in foods such as potato chips, hummus, salad dressings, cookies, cakes and pies. It’s not just seed oils, corn-fed beef also has a much higher ratio of omega-6 to omega-3 than grass-fed beef, which is hard to find in supermarkets because of its high cost and long farming cycle.”

So are omega-6 fatty acids necessarily bad for your health? Yeatman explains: "Omega-6 is an essential fatty acid, and the body needs it, but not in a 30-to-1 ratio with omega-3 fatty acids. The problem is that we overuse seed oils in food, and we can get omega-6 fatty acids from many other sources, so I don't think seed oils are necessarily good for you. Of course, not everyone who is exposed to seed oils will have problems, but there is a very good chance that there is a link. It's hard to prove a link because you need years of dietary history data to prove it. Until we know for sure it's safe, I think the default approach should be to reduce intake."

Although this study has not yet been concluded, it has undoubtedly opened a new window for us to re-examine the intake of ultra-processed foods and seed oils in our daily diet. In the future, more research is needed to further clarify the relationship between them, provide more precise guidance for our healthy diet, help us find a better balance between food and health, stay away from the threat of cancer, and embrace a healthy life.

References:

Ultraprocessed Foods High in Seed Oils Could Be Fueling Colon Cancer Risk｜Scientific American