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Eating a lot of ultra-processed foods significantly increases the risk of colorectal cancer in men and can lead to heart disease and early death in both men and women, according to two new, large-scale human studies in the United States and Italy, published Wednesday in British Medical Journal The BMJ.
Highly processed foods include prepackaged soups, sauces, frozen pizza, ready-to-eat meals, and convenience foods such as hot dogs, sausages, French fries, sodas, store-bought cookies, cakes, candy, donuts, ice cream, and more.
“Literally hundreds of studies have linked ultra-processed foods to obesity, cancer, cardiovascular disease and overall mortality,” said Marion Nestle, Paulette Goddard Professor Emeritus of Nutrition, Food Studies and Public Health at New York University and author of numerous books on food policy and marketing, including 2015’s “Soda Politics: Taking on Big Soda (and Winning).”
“These two studies continue the pattern: ultra-processed foods are unequivocally associated with an increased risk of chronic disease,” said Nestle, which was not involved in either study.
The US-based study examined the diets of more than 200,000 men and women for up to 28 years and found a link between ultra-processed foods and colorectal cancer – the third most diagnosed cancer in the US – in men but not in women.
Processed and ultra-processed meats, such as ham, bacon, salami, hot dogs, beef jerky and beef, have long been associated with a higher risk of bowel cancer in both men and women, according to the World Health Organization, the American Society for with Cancer and the American Institute for Cancer Research.
However, the new study found that all types of ultra-processed foods play a role to some extent.
“We found that men in the highest quintile of ultra-processed food consumption, compared to those in the lowest quintile, had a 29% higher risk of developing colorectal cancer,” said co-author Fang Fang Zhang, a cancer epidemiologist and Chair of the Department of Nutrition Epidemiology and Data Science at the Friedman School of Food Science and Policy at Tufts University in Boston.
This association remained even after the researchers took into account a person’s body mass index or diet quality.
Why didn’t the new study find the same risk for colorectal cancer in women?
“The reasons for such a gender difference are not yet known, but may include the different roles that obesity, sex hormones and metabolic hormones play in men versus women,” Zhang said.
“Alternatively, women may have chosen ‘healthier’ ultra-processed foods,” said Dr. Robin Mendelsohn, a gastroenterologist at Memorial Sloan-Kettering Cancer Center in New York, who was not involved in the study.
The study found that eating “a higher consumption of ultra-processed dairy foods — such as yogurt — was associated with a lower risk of colorectal cancer in women,” Zhang said. “Some ultra-processed foods are healthier, such as whole grains, which contain little or no added sugar, yogurt and dairy products.”
Women had a higher risk of colorectal cancer if they consumed more ready-to-eat or reheated meals such as pizza, she said. However, men are more likely to have a higher risk of bowel cancer if they eat a lot of meat, poultry or ready-to-eat seafood-based products and sugar-sweetened beverages, Zhang said.
“Americans consume a large percentage of their daily calories from ultra-processed foods — 58 percent for adults and 67 percent for children,” she added. “We need to consider replacing ultra-processed foods with unprocessed or minimally processed foods in our diet to prevent cancer and prevent obesity and cardiovascular disease.”
The second study followed more than 22,000 people over a dozen years in the Molise region of Italy. The study, which began in March 2005, was designed to assess cancer risk factors as well as heart and brain diseases.
An analysis published in The BMJ compared the role of nutrient-poor foods – such as foods high in sugar and saturated or trans fats – versus ultra-processed foods in the development of chronic disease and early death. The researchers found that both types of food independently increased the risk of early death, especially from cardiovascular disease.
However, when the researchers compared the two types of food to see which contributed the most, they found that ultra-processed foods were “paramount in determining mortality risk,” said first author Marialaura Bonaccio, an epidemiologist at the department in Epidemiology and Prevention at IRCCS Neurologico Mediterraneo Neuromed in Pozzili, Italy.
In fact, more than 80 percent of the foods classified by the guidelines followed in the study as nutritionally unhealthy were also highly processed, Bonaccio said in a statement.
“This suggests that the increased mortality risk is not directly (or exclusively) due to the poor nutritional quality of some foods, but rather to the fact that these foods are mostly over-processed,” Bonaccio added.
Why are ultra-processed foods so bad for us? For one thing, they are “ready-to-eat or heat-up industrial formulas that are made with ingredients extracted from foods or synthesized in laboratories, with little or no whole foods,” Zhang told CNN.
These overly processed foods are often high in added sugars and salt, low in dietary fiber, and full of chemical additives, such as artificial colors, flavors, or stabilizers.
“Although some ultra-processed foods may be considered healthier than others, in general we would recommend staying away from ultra-processed foods altogether and focusing on healthy, unprocessed foods — fruits, vegetables, legumes,” Mendelsohn said.
In 2019, the National Institutes of Health (NIH) published the results of a controlled clinical trial comparing a processed and unprocessed diet. The researchers found that those on an ultra-processed diet ate faster – and consumed an additional 500 calories more per day than people who ate unprocessed foods.
“On average, participants gained 0.9 kilograms, or 2 pounds, while on the ultra-processed diet and lost an equivalent amount on the unprocessed diet,” notes the NIH.
“There is clearly something about ultra-processed foods that makes people eat more of them without necessarily wanting to or realizing it,” Nestle said.
“The effects of ultra-processed foods are quite clear. The reasons for the effects are not yet known,” Nestle continued. “It would be nice to know why, but until we do, it’s best to advise eating ultra-processed foods as little as possible.”