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Aug. 31 (UPI) -- Men eating lots of ultra-processed foods face a 29% higher risk for developing colorectal cancer than men who consume much smaller amounts, a large, long-term analysis suggests. Researchers said they did not find the same association in women, but they are not sure why.
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Ready-to-eat, ready-to-heat processed foods, from breakfast bars to frozen pizza and packaged sweet snacks -- typically high in added sugar, oils and fats, and refined starch -- now account for 57% of total daily calories eaten by American adults, they said.
The scientists found the strongest association between colorectal cancer and ultra-processed foods among men came from meat, poultry or fish-based, ready-to-eat products such as sausages, bacon, ham and fish cakes.
The findings from research led by Tufts University and Harvard University were published Wednesday in the British Medical Journal.
Colorectal cancer is the fourth-most diagnosed cancer in the United States, after lung, breast and prostate cancer, the Centers for Disease Control and Prevention says.
Nationwide, 142,462 new cases of colon and rectum cancer, and 51,896 deaths from the illnesses, were reported in 2019, according to the CDC's latest available data. For every 100,000 people, 36 new cases were reported.
Among the lifestyle factors that may contribute to colorectal cancer, the CDC cites a diet low in fruit and vegetables, a low-fiber, high-fat diet or a diet high in processed meats.
"We started out thinking that colorectal cancer could be the cancer most impacted by diet compared to other cancer types," Lu Wang, the study's lead author and a postdoctoral fellow at Tufts' Friedman School of Nutrition Science and Policy, said in a news release.
Wang, too, said processed meats, most of which fall into the ultra-processed food category, are a strong risk factor for colorectal cancer.
And ultra-processed foods are also high in added sugars and low in fiber, she said, contributing to weight gain and obesity: an established risk factor for colorectal cancer.
Higher consumption of sugar-sweetened beverages, such as soda, fruit-based beverages and sugary milk-based beverages, also is associated with a higher risk of colorectal cancer in men, the analysis found.
The research involved 200,000-plus participants, including roughly 160,000 women and 46,000 men, across three large studies assessing dietary intake, and followed them for more than 25 years.
Over that time period, the researchers documented 1,294 cases of colorectal cancer among men, and 1,922 cases among women.
Each participant completed a questionnaire every four years asking about the frequency of their consumption of roughly 130 foods. Depending on their intake of ultra-processed foods, they were classified into groups ranging from lowest to highest consumption.
And those in the highest consumption category were identified as being the most at risk for developing colorectal cancer.
The investigators found differences in the type of ultra-processed foods eaten by men and women, and noted that not all ultra-processed foods are equally harmful.
Women, for example, were found to eat more ultra-processed dairy foods, such as yogurt, that may counteract the harmful effects of other types of ultra-processed foods.
And, although ultra-processed foods are often associated with poor diet quality, there could be other factors affecting colorectal cancer risk, such as food additives and contaminants, the scientists said.
The researchers said they adjusted for factors including race, family history of cancer, level of physical activity, smoking status, total alcohol and caloric intake, aspirin use and menopausal status.
In a 2021 study, the Tufts researchers found that ultra-processed foods comprised 67% of the total caloric intake of children and adolescents in 2018, up from 61% in 1999.
