Eating lots of highly processed food such as ready meals is linked to an increased risk of heart disease, bowel 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, disease and ill health. The findings were published in the BMJ.
There is already accumulating evidence that suggests high consumption of ultra-processed foods is associated with a higher risk of several chronic diseases. Few studies have assessed the association between ultra-processed food and bowel cancer risk, though, and previous findings have been mixed due to limitations in study design and sample sizes.
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.
The first study suggests 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 a link to an increased risk of cardiovascular disease and death.
The findings reinforce the importance of reformulating dietary guidelines worldwide, by paying more attention to the degree of processing of foods along with nutrient-based recommendations.
In the first study, researchers examined the association between consumption of ultra-processed foods and risk of colorectal cancer in US adults. Their findings were 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 three decades, taking into account medical and lifestyle factors.
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. The link remained significant even 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 or seafood-based ready-to-eat products and sugar sweetened beverages among men – and ready-to-eat or heat mixed dishes among 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 food and beverages consumed were assessed and deaths were measured over a 14-year period, taking account of underlying medical conditions.
Results showed that those with the least healthy diets compared with those with the healthiest diets had a 19% higher risk of death from any cause and a 32% higher risk of death from heart disease.
Risks were similar when the two highest and lowest categories of ultra-processed food intake were compared (19% and 27% higher for all-cause and cardiovascular mortality, respectively).
A significant proportion of the excess mortality risk associated with a poor diet was explained by a higher degree of food processing. 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 cannot establish cause. Limitations include the possibility that some of the risks may be due to other confounding factors.
Nevertheless, both studies used reliable markers of dietary quality and took account of well known risk factors The findings back up other research linking highly processed food with poor health.