If you're a woman over 50, the foods in your pantry may deserve a second look. New research suggests that those irresistible packaged snacks, sweetened drinks and heat-and-eat favorites, the ultra-processed foods many of us rely on, are quietly raising our risk of developing precancerous colon polyps.

Women who eat the most ultra-processed foods could face a significantly higher risk of developing the precancerous polyps that sometimes lead to early-onset colorectal cancer, a major new study has found. Though the findings are based on data on women, it's likely they apply to men as well.

Ultra-processed foods not only seem to encourage the formation of precancerous polyps, they tend to lack fiber and essential nutrients such as vitamin D, and they're often packed with additives, salt, sugar and artificial sweeteners.

The study followed over 29,000 female nurses under the age of fifty, using data from the respected Nurses' Health Study II. Every four years, the women completed detailed questionnaires, allowing a team of researchers at Mass General Brigham to estimate their intake of ultra-processed foods. It tracked their diet and colonoscopy results from 1991 to 2015.

The numbers tell a compelling and concerning story. Women who averaged three servings a day of ultra-processed foods had about a 3 percent risk of developing adenomas, the type of polyp that can become cancer. But that risk climbed to five percent among those who consumed 10 or more servings (based on caloric intake) daily. In some analyses there was up to a 45 percent higher risk compared with women who ate the least amount of ultra-processed foods.

Importantly, ultra-processed foods were not linked to another, and slower-growing, type of growth called serrated lesions. Instead, the concern centered specifically on adenomas, the more common pathway toward colorectal cancer.

“Our findings support the importance of reducing the intake of ultra-processed as a strategy to mitigate the rising burden of early-onset colorectal cancer. The increased risk seems to be fairly linear, meaning that the more ultra-processed foods you eat, the more potential that it could lead to colon polyps,” gastroenterologist Andrew Chan, the senior author of the study and chief of the Clinical and Translational Epidemiology Unit at Mass General, explained in a press release.

The good news is that adenomas can be removed before they turn cancerous. And prevention can start early with healthier food choices and regular physical activity.

The study wasn't designed to determine cause and effect, but scientists have several theories about what's behind the relationship. One is that ultra-processed foods may alter the gut microbiome, increase inflammation and weaken the gut lining. These disruptions can pave the way for metabolic conditions like obesity and diabetes which themselves raise cancer risk.

Ultra-processed foods also tend to lack fiber and essential nutrients such as vitamin D, and they're often packed with additives, salt, sugar and artificial sweeteners. In the study, women who consumed more processed snacks and sweetened beverages also had higher rates of adenomas.

Colorectal cancer used to be considered a disease of older adults. But cases are rising sharply among people in their 30's and 40's. Many doctors, including Chan, began noticing younger patients long before statistics caught up. Although diet isn't the only culprit, these findings suggest it may play a meaningful role. That's especially relevant considering that ultra-processed foods now make up more than half of the average American's diet.

The good news is that adenomas can be removed before they turn cancerous. And prevention can start early with healthier food choices and regular physical activity. Screening colonoscopies are recommended beginning at age 45, or earlier for those with symptoms or a family history.

As scientists continue to unravel the causes behind early-onset colorectal cancer, one thing is certain: the foods we eat matter. Consider substituting fresh fruits and vegetables, nuts and seeds, and air-popped popcorn for ultra-processed snack foods. Small shifts now toward fresher, less processed meals will help keep your gut healthier for years to come.

The study is published in JAMA Oncology.