Colorectal cancer used to be something doctors mostly saw in older people. But now, more adults under 50 are being diagnosed with this disease, especially in wealthier countries like the United States.
Scientists don’t yet fully understand why this is happening, but a new study from Mass General Brigham offers an important clue.
The study, part of the Cancer Grand Challenges PROSPECT team, points to a possible connection between ultra-processed foods and early-onset colorectal cancer.
Ultra-processed foods are packaged foods that are ready to eat and often contain high levels of sugar, salt, unhealthy fats, and artificial additives. These include chips, sodas, frozen meals, sweetened cereals, instant noodles, and many snack foods.
Over the years, people have been eating more and more of these foods, and this rise in consumption matches the rise in younger people being diagnosed with colorectal cancer.
To find out if the two are connected, the researchers looked at information from the Nurses’ Health Study II, which followed female nurses born between 1947 and 1964. This group is known to be at higher risk of getting colorectal cancer at a younger age.
The study included 29,105 women who had at least two lower endoscopies—procedures used to find early signs of colon cancer—before turning 50. The women also filled out food surveys every four years for 24 years, which allowed the researchers to estimate how much ultra-processed food they were eating.
On average, the women ate about 5.7 servings of ultra-processed foods each day, which made up around 35% of their total calories.
This is a little less than the U.S. national average. After looking at their endoscopy results, the researchers found that 2,787 of the women had developed colon polyps, which are small growths that can sometimes turn into cancer.
The key finding was that women who ate the most ultra-processed food—about 10 servings a day—had a 45% higher risk of developing the type of colon polyp called a conventional adenoma. This type of polyp is strongly linked to early-onset colorectal cancer.
In contrast, women who ate only about three servings a day had the lowest risk. Interestingly, the study found no link between ultra-processed food intake and another type of polyp called serrated lesions, which tend to grow more slowly and are less connected to early-onset cases.
One strength of this study is that the researchers also looked at other known risk factors for colon cancer, such as body weight, diabetes, and fiber intake. Even after considering these factors, the connection between ultra-processed food and adenomas remained strong.
Dr. Andrew Chan, the lead researcher, said that cutting down on ultra-processed foods might be a helpful way to reduce the risk of early-onset colorectal cancer. But he also noted that diet alone doesn’t explain the whole picture. Some young people with colon cancer eat very healthy diets, so scientists are still trying to understand what other factors might be at play.
The team is now working to identify which types of ultra-processed foods might be more dangerous than others and looking for other possible causes behind the rise in colon cancer among young adults. Their goal is to better understand and stop this worrying trend.
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The study is published in JAMA Oncology.
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