Eating more ultra-processed foods is tied to an increased risk of precancerous colorectal growths in women under 50, according to a study published Thursday in JAMA Oncology.
These growths, called adenomas or polyps, can later turn into cancer and are a good indicator of a person’s cancer risk, experts say.
Rates of colorectal cancer in people under 50 have risen sharply in recent decades. The findings could offer new insights into what’s driving this increase.
“One approach we’ve been taking is trying to understand what has changed in our environment that could be driving this. What are some trends that mirror this acceleration in cancer rates?” said study leader Dr. Andrew Chan, a gastroenterologist and the chief of the clinical and translational epidemiology unit at Massachusetts General Brigham in Boston.
Ultra-processed foods now make up the bulk of the average American’s diet, especially among kids. The foods, which tend to be high in calories, have been linked to depression, Type 2 diabetes and early death. Some experts have also suspected eating these foods could be driving the increase in colorectal cancer rates among young people.
To test this hypothesis, Chan and his team used data from more than 29,000 women who participated in the Nurses’ Health Study II, an ongoing study of female registered nurses established in 1989. The women, who were between 24 and 42 when they enrolled in the study, were followed for 24 years, from 1991 through 2015. Every four years, everyone filled out a questionnaire about their diets, and everyone had at least one colonoscopy before 50.
The researchers looked at whether the women were diagnosed with precancerous polyps: either adenomas, which are more likely to turn into cancer, or serrated lesions. While only about 5% of adenomas are cancerous, about 75% of colorectal cancers start as adenomas, according to the Cleveland Clinic. Serrated lesions are still considered precancerous but are linked to fewer cases of colorectal cancer, Chan said.
The study found a connection between eating more ultra-processed foods and developing an adenoma before 50. It didn’t see any links between the foods and serrated lesions.
Because the majority of colon cancers arise from adenomas, the study showing a link between eating more ultra-processed foods and an increased risk of developing adenomas specifically gave Chan and his team more confidence that these foods could increase colorectal cancer risk, he said.
“The strength was that we looked at two major types of polyps — it’s the adenoma type that seems to underlie cancer, and we saw the link between that,” he said. “
About 1,200 women in the study developed adenomas. Compared to those who ate the fewest ultra-processed foods, those who ate the most — accounting for one-third of their daily calories — were about 1.5 times more likely to develop adenomas. Specific foods also appeared to increase risk. Diets higher in sugar and artificial sweeteners were most linked to higher rates of adenomas, followed by diets high in sauces, spreads and condiments.
Although the study included only women, the majority of whom were white, other studies have also found a link between men eating more ultra-processed foods and developing cancer.
“We don’t have any reason to believe there would be a difference in men compared to women,” Chan said, adding that additional research should include men to be sure.
Most colorectal polyps do not turn into cancer, but nearly all colorectal cancer does start as a polyp, said Dr. Folasade May, a gastroenterologist and an associate professor of medicine at the David Geffen School of Medicine at UCLA, who wasn’t involved with the research.
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This is why doctors remove any polyps they find during a colonoscopy, and why people who have polyps are considered to be at higher risk for developing colorectal cancer.
“They are looking at the first step, who is more likely to get these polyps that can turn into cancer,” May said of the study.
The problem is that routine screening for colorectal cancer does not happen until age 45, said Dr. Christopher Lieu, the co-director of gastrointestinal medical oncology at the University of Colorado Anschutz School of Medicine in Aurora.
“The concern is that whenever you have a polyp in a young person, that polyp is allowed to grow unnoticed, and because you are not screening those young patients,” Lieu said. This makes it even more important to identify the modifiable lifestyle factors that are driving increased rates of colorectal cancer in young people, added Lieu, who wasn’t involved with the new research.
Although scientists have yet to determine a clear cause, the rise in rates is unlikely to be driven by genetics, May said.
“This has happened very fast, so it is likely unfortunately something we have done to ourselves as humans, in the way we live our lives,” she said. “It’s jarring, hearing stories every week about people in their 20s, 30s, 40s getting cancers that, when I was in medical school, we were taught happen in people in their 80s.”
Ultra-processed foods cause inflammation in the gut — which includes the colon — that impairs the gut’s ability to repair itself when damaged and keep tumors at bay. High levels of inflammation are also linked to cancer in general, May said. Another hypothesis is that people who eat more ultra-processed foods are more likely to have obesity and Type 2 diabetes, both which are linked to a higher risk for colorectal cancer.
“More likely, it’s the direct toxic effects of these ultra-processed foods,” May said.
Chan, the study author, said ultra-processed foods are known to alter the gut microbiome, which, in theory, could make cells in the gut more likely to turn cancerous.
The next step in the research is determining whether any of these hypotheses appear to have a causal effect on who develops colorectal cancer at a young age. It’s likely part of the puzzle, Chan said.
“One thing that has been clear is that the U.S. intake of ultra-processed food has really risen in the past few decades in a way that mirrors the staggering increase in colorectal cancer cases,” he said.
