High consumption of ultra-processed foods increases the risk of colorectal cancer in men and heart disease and early death in both men and women, according to two large studies conducted in the U.S. and Italy published in The BMJ on Aug. 31.
The U.S.-based study compared the rates of colorectal cancer and relative amounts and types of ultra-processed food consumed by over 200,000 men and women over the course of 24 to 28 years.
In contrast, the Italy study compared adults with nutrient-poor diets and those with high ultra-processed food consumptions, and found that highly processed foods were “associated with poor health outcomes independently of their low nutritional composition, but not the other way around.”
What are ultra-processed foods, and why are they so harmful? As defined by the NOVA classification system, ultra-processed foods have “ingredients predominantly found in industrial food manufacturing, such as hydrogenated oils, high-fructose corn syrup, flavoring agents, and emulsifiers.”
A 2019 National Institutes of Health (NIH) study of 20 adult volunteers found that people “eating ultra-processed foods ate more calories and gained more weight than when they ate a minimally processed diet.”
The differences were present even when the number of calories and macronutrients were the same between the ultra-processed and minimally processed meals.
The volunteers adhered to each diet for two weeks in random order for a total of one month. Participants on the ultra-processed diet ate faster, consumed about 500 more calories per day than those on the unprocessed diet, and gained on average two pounds.
However, those on the unprocessed diet lost two pounds instead.
A practical way to identify ultra-processed products is to check the ingredient list for food substances “never or rarely used in kitchens (such as high-fructose corn syrup, hydrogenated or interesterified oils, and hydrolysed proteins), or classes of additives designed to make the final product palatable or more appealing” such as flavor enhancers, colors, sweeteners, and thickeners, according to a research paper published by Cambridge University Press in February of 2019.
Colorectal cancer risk
In the U.S. study combining three groups of subjects for a total of over 200,000 men and women, 3,216 cases of colorectal cancer were reported during the 24 to 28 years of follow-up.
Colorectal cancer is the third most commonly diagnosed malignancy in the U.S. and second leading cause of death from cancer in the world, with an overall five-year survival rate of 64 percent.
While common risk factors are chronic inflammatory diseases, alcoholism, smoking, and advanced age, this new study suggests that ultra-processed foods should also be included. An estimated 57 percent of total daily calories consumed are from ultra-processed foods, which are “industrial ready-to-eat or ready-to-heat formulations,” the study stated.
Ultra-processed diets are often low in beneficial compounds such as fibers, calcium, and Vitamin D, with food additives that may have pro-inflammatory effects. These diets are “usually high in added sugar, oils/fats, and refined starch, altering gut microbiota composition unfavorably and contributing to increased risk of weight gain and obesity, an established risk factor for colorectal cancer,” researchers noted.
After adjusting results for multiple variables, “Men who consumed ultra-processed foods in the highest fifth had a 29% higher risk of developing colorectal cancer than did those in the lowest fifth.”
While the same association was not found in women, subgroup analyses revealed how the “consumption of yogurt and dairy based desserts was negatively associated with the risk of colorectal cancer among 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,” said co-senior author Fang Fang Zhang, a cancer epidemiologist from Tufts University.
“Alternatively, women may have chosen ‘healthier’ ultra-processed foods,” stated gastroenterologist Dr. Robin Mendelsohn.
All cause and cardiovascular mortality
In the Italy study of over 24,000 men and women aged 35-and-older between 2005 and 2010, all cause and cardiovascular mortality rates were highest in adults “with the lowest quality diet, as measured using the FSAm-NPS dietary index (underpinning the Nutri-Score), and the highest ultra-processed food consumption (NOVA classification).”
While the higher risk of death in individuals with poor nutrient intake was largely associated with higher degrees of food processing, the reverse was not true. In other words, the poor nutritional quality of the food alone did not explain the relationship between intake of ultra-processed foods and mortality.
The authors stress the public health implications of the study and the “opportunity to reformulate dietary guidelines worldwide, by paying more attention to the degree of processing of foods along with nutrient based recommendations.”
The American Heart Association has already made strides in this direction with its recommendation to choose “minimally processed foods instead of ultra-processed foods.”