Studies suggest link between ‘ultra-processed’ foods, cardiovascular disease and all-cause mortality

Two large European studies published in the BMJ in 2019 reported positive associations between consumption of ‘ultra-processed’ foods and risk of cardiovascular disease (CVD) and death. Both studies classified foods by their degree of processing using the NOVA definitions.

The first study was the NutriNet-Santé study which began in 2009 and included 105,159 French adults (21% men, 79% women; mean age 42.7 years). Subjects completed an average of 5.7 (a minimum of two; 7.6% of the cohort only completed two) validated web-based 24-hour dietary questionnaires in the first two years to measure their intake of 3,300 different food items. Follow-up was for an average of 5.2 years, during which 1,409 first incident CVD events occurred. The mean contribution of ultra-processed foods (as weight; as defined by the NOVA classification system) to the diet was 17.6% in men and 17.3% in women and the main contributors were sugary foods (28%), fruit and vegetable products (18%), beverages (16%), starchy foods including breakfast cereals (12%) and processed meat, fish and eggs (11%).

The authors concluded that an absolute 10% increase in the proportion of ultra-processed foods in the diet (by weight) was associated with significantly higher rates of overall cardiovascular disease, coronary heart disease and cerebrovascular disease (increases of 12%, 13% and 11% respectively). The increased risk was 4% for every 100 g/day increase of ultra-processed food in the diet. In contrast, the researchers found a significant association between unprocessed or minimally processed foods and lower risks of overall CVD (9% lower risk of overall CVD, coronary heart diseases and cerebrovascular diseases). A specific limitation of the study is the relatively short length of follow-up (about 5 years) in relation to progression of CVD.

The authors state that further adjustment for the nutritional quality of the diet (i.e. saturated fatty acids, sodium, sugars, intakes of sugary products, fibre, red and processed meat, salty snacks, beverages, fruit and vegetables, fats and sauces and healthy dietary pattern) as well as other confounders such as BMI, smoking, baseline disease risk markers and medication use did not change the results. The authors suggest therefore that it is not just the nutritional composition of ultra-processed foods driving the relationship, but the presence of additives and/or contaminants formed during processing such as acrylamide, however there is currently no clear evidence to suggest such compounds would increase risk of CVD.

The second study was the Seguimiento Universidad de Navarra (SUN) study which was carried out in Spain between 1999 and 2014 and included 19,899 Spanish university graduates (39% men, 61% women; mean age 38 years) who completed a 136-item semi-quantitative food frequency questionnaire every two years. Average follow up time was 10 years, during which 335 deaths occurred (1.7% of the cohort). One hundred and sixty four of the deaths were due to cancer.

The main types of ultra-processed foods (as defined by the NOVA classification system) consumed by the subjects were processed meats (15%), sugars-sweetened beverages (15%), dairy products (including ice cream, custard and milkshakes; 12%), French fries (11%) and pastries and confectionary (10%). The authors stated that higher consumption of ultra-processed foods (more than 4 servings per day) was associated with a 62% increased risk of all-cause mortality compared with lower consumption (less than 2 servings per day). However, this decreased to 44% when repeated measures of dietary intake were taken into account. The data also suggested a dose-response effect, with each additional daily serving of ultra-processed foods increasing mortality risk by 18%, although the definition of a ‘serving’ for the foods considered was not provided. The associations remained after adjustment for intakes of saturated fatty acids, trans fatty acids, added sugars and sodium.

A specific limitation of this study is the small number of food items listed within the food frequency questionnaire used for dietary analysis. The authors state that it was not designed to assess intakes of ultra-processed foods and therefore does not capture all foods that would be classified as ultra-processed. Furthermore, the small number of observed deaths in the cohort meant that some of the analyses were underpowered and importantly, some associations become non-significant when cases of depression and hypertension at baseline were excluded.

Consumption of ultra-processed foods has been previously associated with mortality and conditions such as obesity and cancer. As both of the present studies, and indeed most recent studies published on ultra-processed foods and health, have been observational in design rather than intervention studies, they cannot demonstrate cause and effect. While the researchers in both cases did adjust their data for many established risk factors it is impossible to rule out all confounding and so it is unknown whether the effects seen in this study are genuinely due to consumption of ultra-processed foods or down to generally poorer diet and lifestyle habits among those consuming higher amounts of ultra-processed foods. Furthermore, neither of the cohorts were representative of the general populations of France and Spain, since they both contained more women and were better educated than average and therefore the results may not be generalisable.

The NOVA classification system used in both these studies does not take into account the nutrient content of foods, only the level of processing. According to the NOVA classification system, ultra-processed foods are defined as those that have been manufactured with five or more ingredients and/or contain additives or particular ingredients. Therefore the ‘ultra-processed’ category would include a wide range of foods including items such as confectionary, sugars-sweetened drinks and crisps that are not considered a necessary part of a healthy diet as they contain high levels for fat, sugars and/or salt; along with foods such as fruit yogurts, wholegrain manufactured breads, high fibre fortified breakfast cereals, packaged soups based on vegetables and beans and tomato-based pasta sauces that are often part of healthy dietary patterns. Conversely, some items that are in the ‘less processed’ categories are those that should be limited in the diet, for example sugar and salt (category 2 – processed culinary ingredients) and foods like salted nuts or fruit in syrup (category 3 – processed foods defined as ‘relatively simple’ products). 

Interestingly, among 2,036 foods in the database used for the dietary analysis in the NutriNet-Santé study, 86% of foods that fall within category ‘E’ of the French Nutri-Score five colour labelling system (indicating poor nutritional quality) were classed as ultra-processed according to NOVA whereas 24% of those in category A (indicating good nutritional quality) were also classed as ultra-processed according to NOVA. While the database does not represent all commercially available foods, this highlights that, while there is a greater proportion of ultra-processed foods in the less healthy categories, the NOVA classification and the Nutri-Score system currently being used nationally in France to help consumers identify healthier foods are not always consistent.

Processing can include a wide variety of methods from pickling and fermenting to heat treatment, which may be used in order to make a food edible, safe to eat or to enhance its taste or appearance. In some cases, processing may make a food less healthy, for example by adding high levels of salt in the case of pickled or salted foods or sugar for foods like canned fruit in syrup. There are also specific concerns about some types of processed foods such as processed meats, which are linked to an increased risk of bowel cancer. However in other cases processing may help to make relatively healthy foods more accessible and affordable, for example canned pulses, frozen vegetables or ready prepared vegetable soups. Therefore, when giving dietary advice it is important to consider all the evidence we have on how different foods affect health.

Current advice in the UK is to use the balance of food groups as shown in the Eatwell Guide as the basis of a healthy, balanced diet and to use front-of-pack traffic light labels seen on packaged foods in order to make healthier choices. It is important to note that all additives approved for use in the EU have been rigorously tested for safety.

For more information on how processed foods can fit into a healthy, balanced diet see our FAQ document.

References

Srour B, Fezeu LK, Kesse-Guyot E et al. (2019) Ultra-processed food intake and risk of cardiovascular disease: prospective cohort study (NutriNet-Santé). BMJ 365: l1451.

Rico-Campà A, Martínez-González MA, Alvarez-Alvarez I et al. (2019) Association between consumption of ultra-processed foods and all cause mortality: SUN prospective cohort study. BMJ 365: l1949.