Warnings over ultra-processed food

Ultra-processed foods have been associated with higher incidence of heart disease and mortality in two large European studies, adding to mounting evidence of their health risks.

The foods in question have been industrially modified and typically contain higher fat, sugar, salt and calories, and lower fibre and nutrients, than fresh or minimally processed food.

They include packaged cakes and breads, sweet and savoury snacks, sugary cereals, fizzy drinks, ready-meals with food additives, instant noodles and soups, and reconstituted meat and fish products.

In the first of the new studies, reported in the journal BMJ, Bernard Srour from the University of Paris and colleagues followed more than 100,000 French adults for up to 10 years as part of an online population-based study.

Participants completed three 24-hour dietary recalls spread randomly over two weeks at the study’s inception and again every six months. They provided demographic and health information and their data were linked to national health insurance records.

Foods were classified according to their degree of processing using an established method, NOVA. Other risk factors such as smoking, physical activity, education and family history of heart disease were factored into analyses.

Results showed that each 10% increase in ultra-processed food intake independently conferred a greater than 10% higher risk of heart disease and cerebrovascular disease – a potential precursor for stroke.

The findings held up in all tested models. Conversely, there was no evidence linking the foods in their non-processed form with heart disease.

The second study, also published in BMJ, was led by Maira Bes-Rastrollo and colleagues from the University of Navarra in Spain. It followed nearly 20,000 university graduates over an average of 10 years.

Dietitians took structured food diaries at the beginning of the study and participants provided health and demographic data every two years. The Spanish researchers also used the NOVA system to classify ultra-processed foods.

Potential confounding variables factored into analyses included age, sex, body mass index, education energy intake, smoking, depression, family history of heart disease, physical activity and alcohol intake.

They found that four daily serves of ultra-processed food were associated with 62% higher risk of death from any cause compared with less than two serves. Each additional serve increased the risk by 18%.

It’s important to note that both studies are observational, so cause and effect is not conclusive because other factors could have influenced the results. However, as a strength, they followed people over extended periods of time and controlled comprehensively for other known risk factors.

The Spanish study also coincides with similar findings reported in two large population cohorts in France and the US.

In the French cohort, each 10% increase in ultra-processed food consumption was associated with 14% higher risk of death. The other study found that Americans with the highest quartile of ultra-processed food intake had 31% higher risk of mortality compared to those with the lowest intake.

Since the 1980s, ultra-processed food consumption has steadily increased globally – first in developed countries and more recently in mid- to lower income countries, displacing intake of fresh or minimally processed foods.

These foods have previously been associated with overweight and obesity, metabolic syndrome, dyslipidaemia in children, gastrointestinal disorders, hypertension and cancer risk.

When Srour and colleagues considered whether their finding was an artefact of eating less nutritious foods they found this did not fully explain the connection. 

In addition to sugar, salt and unhealthy fats, they outline several ingredients and processing by-products that have been associated with adverse health effects, reporting that “the health impact of the cumulative intake across all ingested foods and potential cocktail or interaction effects remain virtually unknown”.

These include about 350 additives, emulsifiers, carrageenan (a thickening agent), non-caloric sweeteners, and products formed from heat treatment such as acrylamide and acrolein. The authors propose that processed food might also be contaminated with compounds from plastic packaging, such as bisphenol A (BPA) which has been linked to several health risks.

While further research is needed to unpack the evidence, both teams point out that it would be unethical to expose people to ultra-processed food in a randomised controlled trial. 

As an alternative, Bes-Rastrollo suggests, “participants could be randomised to change their dietary patterns into a rich, unprocessed food dietary pattern … and evaluate the effects on health”.

Nonetheless, a related editorial by Mark Lawrence and Phillip Baker, both from Deakin University in Australia, declares the research has significant implications for dietary guidelines.

“The dietary advice is relatively straightforward: eat less ultra-processed food and more unprocessed or minimally processed food,” the authors write.

Meanwhile, researchers worldwide liken ultra-processed food to tobacco for its health impacts, calling for tight regulation on food industry practices to address the modern pandemic of chronic, lifestyle-related diseases.

Related reading: Study links processed meat and cancers