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WEDNESDAY, Feb. 14, 2018 (HealthDay News) -- If you worry about ever getting cancer, you might want to pass on the processed foods at your supermarket.
Breast cancer, in particular, was associated with greater consumption of mass-produced, ultra-processed foods, according to the study.
But nutritional value might not explain the observed heightened cancer risk, the French researchers said.
"Our results suggest that the lower overall nutritional quality of ultra-processed foods is not the only factor involved in this relationship," said lead author Dr. Bernard Srour, of the University of Paris.
Exactly what it is about these foods or their packaging that might increase cancer risk isn't yet known, said Srour, a biostatistician in the unit of nutritional epidemiology.
"Studies are needed to understand the impact of different dimensions of food processing," he said. These should look at nutritional composition and different additives and contaminants, he added.
Marjorie Lynn McCullough, strategic director of nutritional epidemiology at the American Cancer Society, isn't surprised by the new findings.
"This study supports what we have been recommending for a long time," McCullough said. "This includes eating a mostly plant-based diet rich in vegetables and fruits and eliminating red meat, processed foods and sugars."
In several developed countries, ultra-processed foods may make up as much as 50 percent of the daily diet, the researchers noted.
This includes convenience foods, such as mass-produced baked breads and buns, snacks and cookies -- plus those staples of modern-day childhood, chicken nuggets and fish sticks, Srour said.
Also on the list: instant soups, frozen or ready-to-eat meals, commercially made desserts and products processed with preservatives other than salt -- for example, nitrites.
Many of these items also contain hydrogenated oils, modified starches, colorants, emulsifiers, texturizers, sweeteners and other additives.
The new report was published online Feb. 14 in the BMJ.
The specific risks posed by any or all of these additives are difficult to untangle, experts said.
"We are a long way from understanding the full implications of food processing for health and well-being," wrote Martin Lajous, co-author of an editorial accompanying the study. He is a faculty researcher at the Harvard T.H. Chan School of Public Health in Boston.
Similarly, this study cannot prove that highly processed foods cause cancer, only that an association exists between the two, Srour added.
McCullough said the results should be interpreted with caution. "People eating more highly processed foods are eating fewer healthy foods," she said.
A diet rich in processed foods is apt to increase weight, and increased weight is a known risk factor for several types of cancer, said McCullough, who had no role in the study.
For the study, Srour and his colleagues had nearly 105,000 French men and women, average age 43, complete at least two online dietary questionnaires.
The researchers also examined participants' medical records.
To try to isolate the part foods played in cancer risk, the researchers took into account some well-known risk factors, such as age, gender, educational level, family history of cancer, smoking and physical activity levels.
Besides finding that risk for any cancer rose 12 percent with a 10 percent increase in ultra-processed foods, the researchers looked at several specific cancers.
In addition, other testing uncovered no significant association between cancer risk and less processed foods, such as canned vegetables, cheeses and freshly made bread.
Meanwhile, fresh and minimally processed foods were associated with a lower risk for cancer overall and breast cancer specifically, Srour said. Those foods included fruits, vegetables, rice and pasta, eggs, meat, fish and milk.
However, the study results should be confirmed by other large-scale studies in different populations and settings, Srour said.
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SOURCES: Bernard Srour, Pharm.D., M.P.H., biostatistician, unit of nutritional epidemiology, University of Paris, France; Marjorie Lynn McCullough, S.C.D., R.D., strategic director, nutritional epidemiology, American Cancer Society; Feb. 14, 2018, BMJ