Recent news stories have reported that eating ultra-processed food increases the risk of heart attack and stroke, based on results from two new research studies. The use of the degree of processing of foods as an indicator of their healthfulness is a hotly debated topic in nutrition and food science. So, what exactly did these studies find and how do they add to the debate? Here are a few things to keep in mind when reading the headlines.
The study behind the headlines
The media coverage is based upon two studies that were presented at the 2023 European Society of Cardiology Congress on 25-28 August. The full study information is not available as the results are as yet unpublished. Widespread media reports described the results of the studies as follows:
The first study, carried out by researchers from the Fourth Military Medical University in China, was a systematic review of 10 studies investigating the link between ultra-processed food (UPF) consumption and risk of cardiovascular disease. They concluded that high levels of ultra-processed foods in the diet were associated with an increased risk of cardiovascular events such as heart attack and stroke. They noted that each 10% increase in UPF consumption (as a percentage of daily calorie intake) was linked to a 6% increase in heart disease risk.
The second study, carried out by researchers from the University of Sydney in Australia, was an observational study which investigated the link between UPF intake and cardiovascular disease and high blood pressure in Australian women aged 46-55. Over a 15-year follow up, they found that higher UPF consumption was linked to a higher risk of heart disease and high blood pressure.
The term 'ultra-processed food' was introduced by the NOVA classification system, which defines it as "formulations of ingredients, mostly of exclusive industrial use, made by a series of industrial processes, many requiring sophisticated equipment and technology". However, other classification systems do exist, and it is unclear which definition was used by the researchers in these studies.
What to keep in mind when reading the study's conclusions?
- These results were presented at a conference and peer-reviewed publications are not yet available
The news is based on two conference presentations. The study results have yet to be published in full in a peer-reviewed journal. Although peer-review does not automatically guarantee that the publication is reliable, the independent assessment of the article by academic peers can help to identify possible errors or limitations that may have been overlooked while the research was carried out or during the writing of the article. Full details on the methods, such as the characteristics of those participating, are not available to fully judge study robustness and how generalisable the findings are. It is also unclear which definition of ultra-processed food was used in the two studies.
- The methods used to estimate the levels of ultraprocessed food consumption are unlikely to have been designed or validated for this purpose
Observational studies have shown that consumption of foods categorised as ultra-processed has been linked with less healthy diets overall and with certain health outcomes such as increased risk of obesity, cardiovascular disease or type 2 diabetes. However, these studies often collect data on the consumption levels of UPFs using food frequency questionnaires that have not been validated to do this. This can lead to misclassification of foods in the UPF categories and misinterpretations of health associations. As such, data should be considered with caution, until validated data collection methods have been developed for reliable estimation of UPF consumption.
- The definition of ultraprocessed food is not universally agreed upon
The definition and classification of ultra-processed food is not universally agreed upon by food scientists or nutrition and public health agencies. The most commonly used NOVA classification, which was likely used in these studies, has been criticised for being difficult to apply consistently, and of incorporating aspects other than processing in its classification of foods (for example the addition of ingredients like food additives, the use of low-cost ingredients or emphatic branding). There is also an on-going debate about the usefulness of the term "ultra-processed" when it comes to guiding consumers in their dietary choices, compared to existing food or nutrition-based classifications.
What do other authorities say?
- In 2023, the UK Scientific Advisory Committee on Nutrition (SACN) report on processed food and health concluded that systematic reviews have consistently reported that increased consumption of ultraprocessed foods was associated with increased risks of adverse health outcomes. However there are uncertainties around the quality of the available evidence. Studies are almost exclusively observational and confounding factors such as energy intake, body mass index, smoking and socioeconomic status may not be adequately accounted for. They also state that diets high in (ultra-) processed foods are often energy dense, high in saturated fat, salt or free sugars, high in processed meat, and/or low in fruit and vegetables and fibre. However, it is unclear to what extent observed associations between (ultra-) processed foods and adverse health outcomes are explained by established nutritional relationships between nutritional factors and health outcomes.
- In 2023, a report by the Nordic Nutrition Recommendations (NNR) Committee concluded that there is strong evidence for an association between ultraprocessed foods as a group and weight gain and obesity, while evidence from a limited number of studies (primarily observational) suggest that diets high in ultra-processed foods are associated with an increased risk of hypertension, cancer, type 2 diabetes, depression and premature death. They also state that diets high in ultra-processed foods tend to be nutritionally unbalanced and are less likely to adhere to the overall NNR2023 recommendations than minimally processed foods. In their view, the categorization of foods as ultra-processed foods does not add to the already existing food classifications and recommendations in Nordic Nutrition Recommendations 2023 and as a result they have not formulated any specific recommendations on ultra-processed foods.
- Qu Y et al., (2023) Ultra-processed food consumption and cardiovascular events risk. Presentation at the European Society of Cardiology Congress 2023.
- Pant A et al., (2023) Association of ultra-processe foods with cardiovascular disease and hypertension in Australian women. Presentation at the European Society of Cardiology Congress 2023.
- UK Scientific Advisory Committee on Nutrition (2023) SACN statement on processed food and health.
- New Nordic Nutrition Recommendations 2023. Ultra-processed foods section. Accessed 29 August 2023.