Ultraprocessed foods linked to cancer and early death, studies find

Overly processed foods are often high in added sugars and salt, low in dietary fibre, and full of chemical additives, such as artificial colours, flavours or stabilizers. (Makistock/Adobe Stock/CNN)

Eating a lot of ultraprocessed foods significantly increases men's risk of colorectal cancer and can lead to heart disease and early death in both men and women, according to two new, large-scale studies of people in the United States and Italy published Wednesday in British medical journal The BMJ.

Ultraprocessed foods include prepackaged soups, sauces, frozen pizza, ready-to-eat meals and pleasure foods such as hot dogs, sausages, french fries, sodas, store-bought cookies, cakes, candies, doughnuts, ice cream and many more.

"Literally hundreds of studies link ultra-processed foods to obesity, cancer, cardiovascular disease, and overall mortality," said Marion Nestle, the Paulette Goddard professor emerita of nutrition, food studies and public health at New York University and author of numerous books on food politics and marketing, including 2015's "Soda Politics: Taking on Big Soda (and Winning)."

"These two studies continue the consistency: Ultraprocessed foods are unambiguously associated with an increased risk for chronic disease," said Nestle, who was not involved in either study.

A LINK TO CANCER

The U.S.-based study examined the diets of over 200,000 men and women for up to 28 years and found a link between ultraprocessed foods and colorectal cancer -- the third most diagnosed cancer in the U.S. -- in men, but not women.

Processed and ultraprocessed meats, such as ham, bacon, salami, hotdogs, beef jerkey and corned beef, have long been associated with a higher risk of bowel cancer in both men and women, according to the World Health Organization, American Cancer Society and the American Institute for Cancer Research.

The new study, however, found that all types of ultraprocessed foods played a role to some degree.

"We found that men in the highest quintile of ultraprocessed food consumption, compared those in the lowest quintile, had a 29% higher risk of developing colorectal cancer," said co-senior author Fang Fang Zhang, a cancer epidemiologist and chair of the division of nutrition epidemiology and data science at the Friedman School of Nutrition Science and Policy at Tufts University in Boston.

That association remained even after researchers took into account a person's body mass index or dietary quality.

Why didn't the new study find the same risk for colorectal cancer in women?

"Reasons for such a sex difference are still unknown, but may involve the different roles that obesity, sex hormones, and metabolic hormones play in men versus women," Zhang said.

"Alternatively, women may have chosen 'healthier' ultraprocessed foods," said Dr. Robin Mendelsohn, a gastroenterologist at Memorial Sloan-Kettering Cancer Center in New York City, who was not involved in the study.

The study did find that eating a "higher consumption of ultraprocessed dairy foods -- such as yogurt -- was associated with a lower risk of colorectal cancer in women," Zhang said. "Some ultraprocessed foods are healthier, such as whole-grain foods that contain little or no added sugars, and yogurt and dairy foods."

Women did have a higher risk for colorectal cancer if they consumed more ready-to-eat-or-heat dishes such as pizza, she said. However, men were more likely to have a higher risk of bowel cancer if they ate a lot of meat, poultry, or seafood-based ready-to-eat products and sugar-sweetened beverages, Zhang said.

"Americans consume a large percentage of their daily calories from ultraprocessed foods -- 58% in adults and 67% in children," she added. "We should consider substituting the ultraprocessed foods with unprocessed or minimally processed foods in our diet for cancer prevention and prevention of obesity and cardiovascular diseases."

A LINK TO EARLY DEATH

The second study followed more than 22,000 people for a dozen years in the Molise region of Italy. The study, which began in March 2005, was designed to assess risk factors for cancer as well as heart and brain disease.

Analysis published in The BMJ compared the role of nutrient-poor foods -- such as foods high in sugar and saturated or trans-fats -- versus ultraprocessed foods in the development of chronic disease and early death. Researchers found that both types of foods independently increased the risk of an early death, especially from cardiovascular diseases.

However, when researchers compared the two types of food to see which contributed the most, they discovered that ultra-processed foods were "paramount to define the risk of mortality," said first author Marialaura Bonaccio, an epidemiologist at the department of epidemiology and prevention at the IRCCS Neurologico Mediterraneo Neuromed of Pozzilli, Italy.

In fact, over 80% of the foods classified by the guidelines followed in the study as nutritionally unhealthy were also ultraprocessed, said Bonaccio in a statement.

"This suggests that the increased risk of mortality is not due directly (or exclusively) to the poor nutritional quality of some products, but rather to the fact that these foods are mostly ultraprocessed," Bonaccio added.

NOT REAL FOODS

Why are ultraprocessed foods so bad for us? For one, they are "ready-to-eat-or-heat industrial formulations 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.

"While some ultraprocessed foods may be considered healthier than others, in general, we would recommend staying away from ultra-processed foods completely and focus on healthy unprocessed foods -- fruits, vegetables, legumes," Mendelsohn said.

In 2019, the National Institute of Health (NIH) published the results of a controlled clinical trial comparing a processed and unprocessed diet. Researchers found those on the ultraprocessed diet ate at a faster rate -- and ate an additional 500 calories more per day than people who were eating unprocessed foods.

"On average, participants gained 0.9 kilograms, or 2 pounds while they were on the ultraprocessed diet and lost an equivalent amount on the unprocessed diet," the NIH noted.

"There is clearly something about ultraprocessed foods that makes people eat more of them without necessarily wanting to or realizing." said Nestle.

"The effects of ultraprocessed 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 find out, it's best to advise eating ultraprocessed foods in as small amounts as possible."