First-of-its-kind study may help explain why colorectal cancers are rising sharply in young people

By Kristen Rogers, CNN

(CNN) — As colon and rectal cancers in young people are on the rise globally, especially in the United States, consumption of ultraprocessed foods has been in lockstep. The fare now makes up roughly 70% of the US food supply and nearly 60% of US adult caloric intake, and several studies have linked this growing trend with the risk of such cancers.

A new, first-of-its-kind study adds to the growing evidence by suggesting eating ultraprocessed foods may significantly raise the odds of developing early-age noncancerous colorectal adenomas — growths, or polyps, in the colon and rectum that can lead to cancer.

In the new study, ultraprocessed food intake was primarily from ultraprocessed breads and breakfast foods; sauces, spreads and condiments; and sugar- or artificially sweetened beverages.

Participants with the highest intake of ultraprocessed foods — about 10 servings daily — had a 45% higher risk of developing those growths by age 50 when compared with those with the lowest consumption, a bit over three servings daily. The study, which followed more than 29,100 female nurses for a median period of 13 years, published Thursday in the journal JAMA Oncology.

“Our study isn’t cause and effect, so we can’t say that this is definitive,” said senior study author Dr. Andrew Chan, a gastroenterologist at the Mass General Brigham Cancer Institute in Boston. “But it does serve as some clues that what we eat may play a role. So, as we move forward, I think it’s helpful to think about where it is that we can potentially limit our intake and lay the groundwork for future studies for us to be able to identify, more specifically, the mechanisms and the specific foods.”

“To the extent possible, you should try to avoid UPFs and build your diet out of real, whole foods, as direct from nature and minimally processed as possible,” Dr. David Katz, founder of the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine, said via email. He wasn’t involved in the study.

“The best diets, leading to the best health outcomes, are comprised mostly of vegetables, fruits, whole grains, beans/legumes, nuts and seeds, and plain water,” added Katz, founding director of the Yale University Prevention Research Center in Connecticut.

Read ingredient labels and be aware of how much sodium you’re eating and how different foods make you feel — ultraprocessed foods can keep you wanting more, whereas whole foods are more satisfying, experts told CNN in a February report.

Noncancerous colorectal tumors usually don’t have symptoms, but when they grow large enough, they can cause problems worth seeing a doctor about, experts said. These include dark or bloody bowel movements, pain, iron-deficiency anemia, unintended weight loss in combination with gastrointestinal symptoms, and blockage-induced constipation.

You should also get screened starting at age 45 or if you have a family history of colorectal cancer, Dr. Robin Mendelsohn said, as the earlier issues are diagnosed, the sooner and more effectively they can be treated. Mendelsohn is codirector of the Center for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Center in New York. She wasn’t involved in the study.

Ultraprocessed food consumption and health over time

Ultraprocessed foods are made with industrial techniques and some ingredients “never or rarely used in kitchens,” according to the Food and Agriculture Organization of the United Nations. These foods are typically low in fiber and high in calories, added sugar, refined grains and fats, sodium and additives, all of which are designed to help make food more appealing.

Additives often include preservatives to maintain freshness and texture or resist mold and bacteria, and emulsifiers to prevent ingredients from naturally separating. Other common additives include fragrance and flavor enhancers and agents for anti-foaming, bleaching, bulking, gelling and glazing.

The study participants were part of the Nurses’ Health Study II, an ongoing study established in 1989 to follow female nurses born between 1947 and 1964 to learn about risk factors for major chronic diseases in women.

The women answered an initial diet questionnaire in 1991; every four years they were asked to recall their dietary choices over the past 12 months.

As with most nutrition studies, this type of recollection can be limited in accuracy. “I don’t remember what I ate last week, and people may not tell the entire truth,” Mendelsohn said via email.

Additionally, classification of ultraprocessed foods and the determination of which ones are more harmful than others still need work, Chan said, and that ability would help experts more specifically determine health effects and dietary guidance. However, the researchers contend that the participants may be better than the average person at accurately providing such details, given their background in nursing.

Most of the colorectal tumors were discovered via endoscopy before 2015, “which is before the age for (initial) screening was decreased to 45,” Mendelsohn said. “So if people were getting screening (endoscopies) we have to assume they were at increased risk of colorectal cancer — i.e., from family history — and that’s why they were being screened earlier. And, of course, if done for symptoms, there is an increased rate of finding polyps.” Whether these tumors became cancerous is also unknown.

One of the study’s strengths was “detailed information about other colorectal cancer risk factors in the participants, such as body mass index, type 2 diabetes, and low fiber intake,” Chan said in a news release. “Even after accounting for all these other risk factors, the association with ultra-processed foods still held up.”

While the risk for precancerous growths increased the more ultraprocessed foods participants ate, the odds for developing serrated lesions — another type of precancerous polyp and the other main pathway for colorectal cancer — did not. That finding suggests ultraprocessed foods may cause biological processes that turn classic adenomas into cancerous tumors, said Dr. Ganesh Halade, a member of the Cancer Biology Program at the Tampa General Hospital Cancer Institute, who wasn’t involved in the research.

Importantly, ultraprocessed foods of the 1990s “are not identical to today’s products,” Halade added, “given changes in formulations, the introduction of novel additives, and shifts in the proportion of UPFs in the diet.”

“However, one consistent feature across those decades has been the widespread use of omega-6-rich seed oils, which may be a key dietary factor contributing to early-onset colorectal cancer,” Halade said via email.

Any potential relationship between ultraprocessed foods and colorectal tumors may be explained by the foods possibly altering the gut microbiome and its protective lining, causing chronic inflammation and producing toxic molecules when metabolized, Mendelsohn and Chan said.

“Indirectly, consumption of ultraprocessed foods is associated with obesity, which is also a risk factor for colorectal cancer,” Mendelsohn added.

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