Study offers clues on rise of colorectal cancer in women under 50

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Women who eat more ultra-processed foods on a daily basis have a greater risk of developing colorectal polyps before age 50 when compared with women who consume far less of the processed foods, a new study has found.

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While not every colon polyp turns into cancer – in fact, they usually don’t – the findings do suggest one possible reason that colorectal cancer rates are on the rise in adults under 50. Ultra-processed food often contain less fiber and more sugar, salt, fat and additives than minimally processed or whole foods.

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The observational study found that women who reported consuming nine to 10 daily servings of ultra-processed foods seemed to have a 45 percent greater likelihood of getting colon polyps before the age of 50 – as compared with women who had the least amount of ultra-processed foods (three servings a day, on average).

The study’s results highlight an association and not a cause-and-effect relationship, said Andrew T. Chan, the senior author of the study and a gastroenterologist at the Mass General Brigham Cancer Institute.

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“It gives us some clues into the potential role of diet in the development of early-onset colorectal cancer precursor lesions,” Chan said. “And I think it is probably the best available data we have now.”

There’s around a 5 percent risk that the average colon polyp may develop into cancer over time, Chan said.

“But we think even the smallest, most benign polyps probably have some malignant potential if they’re left in place without any treatment,” Chan said. “That risk becomes much greater as the polyp gets bigger.”

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What the study found

Colorectal cancer has been on the rise in people under the age of 50 in recent decades. And typical risk factors such as obesity, smoking or sedentary behavior don’t fully explain the trend, Chan said.

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Meanwhile, there’s been a marked increase in the amount of processed foods in the American diet. More than half of the calories that Americans consume come from ultra-processed foods. This study is part of a global scientific effort to determine why more young people are getting colon cancer.

“We wanted to know if these things were related,” Chan said. “Is it possible that some of the rising incidence of early-onset colorectal cancer could be explained by our increasing consumption of ultra-processed foods?”

To address this question, researchers examined 24 years of health and dietary records from 29,105 women, younger than 50, enrolled in a decades-long study of female nurses in the U.S. (Women who already had a history of cancer, colorectal polyps or inflammatory bowel disease were excluded from the study.)

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Every four years, from 1991 to 2015, the nurses answered a questionnaire about what they ate and how often; and the researchers used those answers to determine the ultra-processed foods participants regularly consumed.

On average, ultra-processed foods accounted for 35 percent of total daily calories in the cohort, and the most common were breads and breakfast foods, sauces and condiments, and sugar or artificially sweetened beverages. But the researchers didn’t find “a single culprit” among the types of ultra-processed foods, Chan said.

The researchers examined the nurses’ dietary patterns alongside the results of endoscopies taken before participants turned 50 years old. Over 24 years, there were 1,189 documented cases of colon polyps called conventional adenomas.

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What the researchers found was that a higher intake of ultra-processed foods was associated with an increased likelihood of these colon polyps before women turned 50, Chan said. And that association remained even after researchers adjusted for participants’ BMI, cases of Type 2 diabetes and other qualities of participants’ diets (such as the amount of fiber they ate).

“We’re not trying to alarm people. And we’re not telling people that eating any [ultra-processed food] is going to lead to colon cancer,” Chan said. “We think it’s one piece of the puzzle; that there’s many things that contribute to colon cancer risk and this is something to be aware of.”

Sarah Berry, a professor of nutritional sciences at King’s College London and a co-author of the study, said the findings add “to the growing body of evidence that following a balanced, healthy diet is important for many chronic diseases.”

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Processed foods tend to be lower in fiber and polyphenols (which have anti-inflammatory properties) but higher in salt and saturated fat, Berry said. And, processed foods often have additives and emulsifiers that may affect your gut microbiome, she said.

But Berry said the term “ultra-processed” refers to a wide range of products – “some of which are unhealthy, and some of which may even be healthy.”

“Every food is processed in a different way,” she said. So, we can’t assume all processed food increases a person’s risk of colorectal cancer, she said.

Study participants were mostly well-educated, White female nurses who had better access to medical care than the general population. So, the findings may not be applicable to a broader group of Americans. And the nurses in the study self-reported their diets, which could’ve led to some misclassification.

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What other researchers say

Dalia Perelman, a research dietitian at Stanford University who wasn’t involved in the research, said this is a well-designed study that “strengthens the evidence” that ultra-processed foods may play a role “in the disease process.”

“There are very few existing epidemiologic studies in which we can investigate early-onset cancers, as they are still relatively rare,” said Leah Ferrucci, an assistant professor of epidemiology at Yale School of Public Health who also was not involved in the study.

“So, this is an important new piece of evidence” that could help fund and launch further study, she said.

The association between ultra-processed foods and polyps could help researchers understand why we are seeing more cases of colorectal cancer in younger people, Ferrucci said. But it’s possible ultra-processed foods are associated with the development of polyps but not the progression to cancer, she said.

For now, Perelman said her message is for people to start shifting their diet away from processed, packaged or preprepared meals and toward “more simple, whole ingredients.”

You can choose a handful of nuts instead of a bag of Cheetos, she said. Or, plain oatmeal with a little maple syrup instead of ready-to-eat cereals.

“It doesn’t have to be complicated,” Perelman said. “And it certainly doesn’t have to be perfect.”

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