Eating a lot of highly processed foods, such as ready meals, has been linked to an increased risk of heart disease, colon cancer and premature death, according to two large studies.
The research offers more reasons to limit intake of ultra-processed foods and instead consume more unprocessed or minimally processed foods to reduce the risk of death, illness and ill health. The findings were published in the BMJ.
There is already mounting evidence to suggest that high consumption of ultra-processed foods is associated with a higher risk of several chronic diseases. However, few studies have assessed the association between ultra-processed foods and colon cancer risk, and previous findings have been mixed due to limitations in study design and sample size.
Ultra-processed foods include packaged bakery products and snacks, carbonated beverages, sugary grains, and ready-to-eat or hot foods, often with lots of added sugars, fats and/or salt, but without vitamins and fiber.
The first study suggests that high consumption of ultra-processed foods in men and some subgroups of ultra-processed foods in men and women is associated with an increased risk of colorectal cancer. The second study found an association with an increased risk of cardiovascular disease and death.
The findings reinforce the importance of reformulating dietary guidelines worldwide, by paying greater attention to the degree of food processing along with nutrient-based recommendations.
In the first study, researchers examined the association between consumption of ultra-processed foods and colorectal cancer risk in American adults. Their findings were based on 46,341 men and 159,907 women from three large surveys of U.S. health professionals whose dietary intake was assessed every four years using detailed food frequency questionnaires.
Foods were grouped by degree of processing and colorectal cancer cases were measured over a three-decade period, taking into account medical and lifestyle factors.
The results show that men in the highest fifth of consumption, compared with those in the lowest fifth of ultra-processed food consumption, had a 29% higher risk of developing colorectal cancer. The link remained significant even after further adjustment for body mass index or nutritional quality.
No association was found between overall consumption of ultra-processed foods and colorectal cancer risk in women. However, higher consumption of ready-to-eat meat, poultry or seafood and sugar-sweetened beverages in men – and ready-to-eat or hot mixed dishes in women – was associated with an increased risk of colorectal cancer.
The second study was based on 22,895 Italian adults. Both the quantity and quality of foods and drinks consumed were assessed and mortality was measured over a 14-year period, taking into account underlying medical conditions.
The results showed that compared to those on the healthiest diets, those on the least healthy diet had a 19% higher risk of death from any cause and a 32% higher risk of death from heart disease.
The risks were similar when the two highest and lowest categories of ultra-processed food intake were compared (19% and 27% higher for all-cause mortality and cardiovascular mortality, respectively).
A significant portion of the additional mortality risk associated with poor nutrition was explained by higher levels of food processing. Ultra-processed food intake remained associated with mortality even after taking into account the poor nutritional quality of the diet.
Both studies are observational and thus cannot determine a cause. Limitations include the possibility that some of the risks are due to other confounding factors.
Nevertheless, both studies used reliable food grade markers and took into account known risk factors. The findings support other research linking highly processed foods to poor health.