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NEW YORK (CNN) — Ultra-processed foods are not known for their health qualities. We know this, yet it's hard to resist the doughnuts your kind colleague brought into the office. Now, research published Wednesday in the BMJ may give you at least a longer pause before you pick the pink one with sprinkles.
Researchers discovered that people who eat more ultra-processed foods have a higher risk of cancer. Such foods are the ones with unrecognizable and unpronounceable words on the list of ingredients — anything from the candy that turns your tongue blue to healthier-sounding canned soups packed with artificial flavors, additives or emulsifiers. Most food is processed to some degree, but ultra-processed foods are typically much more calorie-, sodium- and sugar-packed.
Research has long showed that people who live on ultra-processed food tend to be more obese and overweight. They're also more likely to have heart and circulation problems or diabetes, studies have found. Eating a lot of processed meat like hot dogs has also been tied to an increased risk of colorectal cancer.
Researchers saw this new cancer link when they analyzed 24-hour dietary records of nearly 105,000 adults in the NutriNet-Sante cohort, a general population group in France. The individuals recorded what they ate from a list of 3,300 food items that were then categorized by how processed they were, using a system called NOVA.
What the scientists found was that a 10 percent increase in the proportion of ultra-processed foods in the diet was associated with a significant increase of greater than 10 percent in risks for overall cancer and breast cancer.
"Ultra-processed fats and sauces, sugary products and drinks were associated with an increased risk of overall cancer," the study says. "Ultra-processed sugary products were associated with an increased risk of breast cancer."
People who tended to eat more ultra-processed food also tended to smoke more and exercise less than the others, but the authors controlled for these issues and still found the elevated cancer risk.
Boxed macaroni and cheese, potato chips and drive-thru hamburgers are some types of unhealthy processed foods.
Processed food falls on a spectrum from minimally to heavily processed:
- Minimally processed foods — such as bagged spinach, cut vegetables and roasted nuts — often are simply pre-prepped for convenience.
- Foods processed at their peak to lock in nutritional quality and freshness include canned tomatoes, frozen fruit and vegetables, and canned tuna.
- Foods with ingredients added for flavor and texture (sweeteners, spices, oils, colors and preservatives) include jarred pasta sauce, salad dressing, yogurt and cake mixes.
- Ready-to-eat foods — such as crackers, granola and deli meat — are more heavily processed.
- Pre-made meals are the most heavily processed foods, including frozen pizza and microwaveable dinners.
"It was quite surprising, the strength of the results. They were really strongly associated, and we did many sensitive analysis and adjusted the findings for many co-factors, and still, the results here were quite concerning," study co-author Mathilde Touvier said.
"What people eat is an expression of their lifestyle in general and may not be causatively linked to the risk of cancer. So it is necessary to rule out what are called cofounding factors," said Tom Sanders, scientific governor of the British Nutrition Foundation and an emeritus professor at King's College London.
Sanders, who was not involved in the study, said the authors made statistical adjustments to accommodate for some of that, but he cautions that "the approach of categorizing dietary patterns that depend on industrially processed food in relation to disease risk is novel but probably needs refining before it can be translated into practical dietary advice."
The nonprofit trade group Association of Food Industries did not respond to requests for comment.
Marji McCullough, strategic director of nutritional epidemiology at the American Cancer Society, suggests caution about interpreting what is responsible for the cancer risk associatedwith ultra-processed food.
"This study doesn't mean that people should think 'if I eat this cracker, I'm going to get cancer,' " McCullough said. "The overriding message of this study was really to look at an overall diet pattern rather than a specific ingredient, and it supports a lot of what we already know."
For example, she said, people eating more highly processed foods are probably eating fewer healthy foods, which may help prevent cancer. Nutritionists recommend a diet rich in whole grains, whole fruits and vegetables instead of foods that have little nutritional value.
Touvier also noted that it's an observational study, meaning scientists don't know what exactly is causing the increased cancer risk, but her group at the Sorbonne Paris Cité Epidemiology and Statistics Research Center plans to look closer at what the connection may be. "The challenge now is to disentangle the different foods and understand this relationship to see what specifically is having this effect."
Animal studies have shown that some additives are "quite good candidates" for being carcinogenic, Touvier said, "but that would need to be seen if they are also carcinogenic in the human population."
If you are starting to worry about what you've brought for lunch, Touvier cautions not to be "too alarmist" about this research.
However, ultra-processed foods occupy a growing part of the world's diet. A 2016 study found that 60 percent of the calories in the average American diet come from this kind of food. A 2017 study found that they make up 50 percent of the Canadian diet, and they make up more than 50 percent of the UK diet. And more of the developing world is starting to eat this way.
A balanced and diversified diet should be considered one of the most important public health priorities, the authors advise. "Eat real food and try to limit ultra processed items," Touvier said. "At least until we know more."
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