Two large studies published by The BMJ this week find links between high consumption of ultra-processed foods and increased risks of cardiovascular disease, bowel (colorectal) cancer and death.
The findings add further evidence in support of policies that limit ultra-processed foods and instead promote eating unprocessed or minimally-processed foods to improve public health worldwide.
Ultra-processed foods include packaged baked goods and snacks, fizzy drinks, sugary cereals, and ready-to-eat or heat products, often containing high levels of added sugar, fat, and/or salt, but lacking in vitamins and fibre.
Previous studies have linked ultra-processed foods to higher risks of obesity, high blood pressure, cholesterol, and some cancers, but few studies have assessed the association between ultra-processed food intake and colorectal cancer risk, and findings are mixed due to limitations in study design and sample sizes.
In the first study, researchers examined the association between consumption of ultra-processed foods and risk of colorectal cancer in US adults.
Their findings are based on 46,341 men and 159,907 women from three large studies of US health professionals whose dietary intake was assessed every four years using detailed food frequency questionnaires.
Foods were grouped by degree of processing and rates of colorectal cancer were measured over a period of 24-28 years, taking account of medical and lifestyle factors.
29% increase in colorectal cancer risk
Results show that compared with those in the lowest fifth of ultra-processed food consumption, men in the highest fifth of consumption had a 29% higher risk of developing colorectal cancer, which remained significant after further adjustment for body mass index or dietary quality.
No association was observed between overall ultra-processed food consumption and risk of colorectal cancer among women. However, higher consumption of meat/poultry/seafood based ready-to-eat products and sugar sweetened beverages among men – and ready-to-eat/heat mixed dishes among women – was associated with an increased risk of colorectal cancer.
In the second study, researchers analysed two food classification systems in relation to mortality – the Food Standards Agency Nutrient Profiling System (FSAm-NPS), used to derive the colour-coded Nutri-Score front-of-pack label, and the NOVA scale, which evaluates the degree of food processing.
Their findings are based on 22,895 Italian adults (average age 55 years; 48% men) from the Moli-sani Study, investigating genetic and environmental risk factors for heart diseases and cancer.
Both the quantity and quality of food and beverages consumed were assessed and deaths were measured over a 14 year period (2005 to 2019), taking account of underlying medical conditions.
Results showed that those in the highest quarter of the FSAm-NPS index (least healthy diet) compared with the lowest quarter (healthiest diet) had a 19% higher risk of death from any cause and a 32% higher risk of death from cardiovascular disease.
Risks were similar when the two extreme categories of ultra-processed food intake on the NOVA scale were compared (19% and 27% higher for all-cause and cardiovascular mortality, respectively).
Effects of ultra-processing revealed
A significant proportion of the excess mortality risk associated with a poor diet was explained by a higher degree of food processing. In contrast, ultra-processed food intake remained associated with mortality even after the poor nutritional quality of the diet was accounted for.
Both studies are observational so can’t establish cause, and limitations include the possibility that some of the risks may be due to other unmeasured (confounding) factors.
Nevertheless, the researchers say, both studies used reliable markers of dietary quality and took account of well known risk factors, and the findings back up other research linking highly processed food with poor health.
As such, both research teams say their findings support the public health importance of limiting certain types of ultra-processed foods for better health outcomes in the population. Results from the Italian study also reinforce the opportunity to reformulate dietary guidelines worldwide, by paying more attention to the degree of processing of foods along with nutrient based recommendations.
In a linked editorial, Brazilian researchers argue that nobody sensible wants foods that cause illness.
The overall positive solution, they say, includes making supplies of fresh and minimally processed foods available, attractive, and affordable. And sustaining national initiatives to promote and support freshly prepared meals made with fresh and minimally processed foods, using small amounts of processed culinary ingredients and processed foods.
“Enacted, this will promote public health. It will also nourish families, society, economies, and the environment,” they conclude.