Two recent widely-publicised international studies, which found people who ate the most ‘ultra-processed’ food were more likely to have a heart attack or stroke, or to die sooner, are assessed by the UK’s NHS in its Behind the Headlines section.
The NHS writes:
The term “ultra-processed food” is generally understood to refer to food that’s gone through multiple food manufacturing processes in order to make it cheap or tasty, or both. But there are questions about the studies, including whether the definitions of ultra-processed food used by the researchers are reliable or helpful.
Some experts have questioned why, for example, cheese was not classed as ultra-processed while salami was, even though cheese-making involves numerous processing steps and additives.
It’s also notoriously difficult to prove direct cause and effect from such studies.
For example, people who eat more heavily processed food may have a generally poorer diet and a less healthy lifestyle, and it’s the combination of numerous factors that increases risk.
It’s also unclear whether the study populations (volunteers in France and Spain) are representative of the general population, including that of the UK. We do know, however, that eating plenty of fresh fruit and vegetables, limiting sugar and salt, and eating less fatty food is likely to benefit our health.
The researchers who carried out the studies were from the University of Paris and the University of Montpellier in France, and the University of Navarra in Spain. The studies were funded by the Ministère de la Santé, Santé Publique France, INSERM, Institut de la Recherche Agronomique, Conservatoire National des Arts et Métiers and Université Paris 13.
The report says cohort studies are good at finding patterns and links between 1 factor (in both these studies, the proportion of processed food in the diet) and others (in one study, death from any cause and in the other, cardiovascular disease). But they cannot prove that one factor directly causes the other. Other confounding factors may be involved.
The report says the larger French study looked at the link with cardiovascular disease recruited adult volunteers in France by advertisements, starting in 2007. The volunteers were asked to complete questionnaires about their lifestyle, height and weight, physical activity and health status. They were then asked to complete three non-consecutive 24-hour dietary records. They recorded everything they ate over a 24-hour period at the start of the study and again every six months throughout the study.
Of these, 105,159 volunteers provided sufficient information.
Researchers used the first two years of dietary records to classify people’s average intake of food in four groups: unprocessed or minimally processed (such as fresh, dried, chilled, frozen, pasteurised or fermented foods); processed culinary ingredients (such as salt, vegetable oils, butter, sugar); processed foods (such as canned vegetables with added salt, sugar-coated dried fruit, meat products preserved only by salting, freshly made unpackaged bread); and ultra-processed foods (such as mass-produced packed bread, packaged snacks, sweets and desserts, fizzy drinks, meatballs, chicken nuggets and fish fingers, instant noodles and soups, ready meals)
Researchers calculated how much of their diet consisted of each class of food by weight.
They followed people up each year from recruitment until 2018 to see if they developed cardiovascular disease (stroke or transient ischaemic attack [mini-stroke], heart attack and related conditions).
Where possible, they linked to French health records to confirm this.
The researchers compared what happened to people in the quarter of the group that ate the least amount of ultra-processed food with what happened to those in the quarter who ate the most. They also estimated the change in risk of cardiovascular disease for each additional 10% of the diet given over to ultra-processed food.
The report says the smaller Spanish study into death began in 1999 and was carried out among 19,899 Spanish students aged 20 and above who completed food frequency questionnaires. The researchers at University of Navarra, Spanish National Institute of Health Carlos III, IDISNA, Navarra Institute for Health Research, Harvard TH Chan School of Public Health, and the Federal University of Minas Gerais, Brazil, estimated people’s frequency of consuming food based on the same food groups as used in the French study. They compared the risk of having died from any cause between 1999 and 2014 for people who ate the most and least ultra-processed food. They grouped people into consuming 1 or less, 2, 3 to 4, or more than 4 servings a day.
In both studies researchers adjusted their figures to take account of a wide range of possible confounding risk factors, including: age; gender; smoking; body mass index; family history of disease; educational level; daily calorie intake; and physical activity.
The French study looking at cardiovascular disease reported that 1,409 people out of 105,159 (1.3%) developed cardiovascular disease over an average of 5.2 years of follow-up. Ultra-processed food made up 17% to 18% of diet by weight on average.
The researchers found: people who ate most ultra-processed food had a 25% increased risk of getting cardiovascular disease, compared with those who ate the least (hazard ratio [HR] 1.25, 95% confidence interval [CI] 1.05 to 1.47); the rate of cardiovascular disease among people who ate the most ultra-processed food was 277 events per 100,000 people a year, while the rate among those who ate the least was 242 per 100,000 people a year; and each 10% increase in the proportion of the diet made up by ultra-processed food increased the chances of getting cardiovascular disease by 12% (HR 1.12, 95% CI 1.05 to 1.20)
In the Spanish study, 335 of 19,899 people (1.7%) died over an average of 10.4 years of follow-up.
The researchers found: people who ate the most ultra-processed food had a 62% increased risk of death, compared with those who ate the least (HR 1.62, 95% CI 1.13 to 2.33); and each additional serving of ultra-processed foods increased the chances of having died by 18% (HR 1.18, 95% CI 1.05 to 1.33).
Interpreting the results, French researchers said: “These results need to be confirmed in other populations, and causality remains to be established.” But they said it was “important to inform consumers about these associations and to implement actions targeting product reformulation (improving nutritional quality and reducing the use of unnecessary additives), taxation and communication to limit the proportion of ultra-processed foods in the diet.”
The Spanish researchers said: “Discouraging the consumption of ultra-processed foods; targeting products, taxation, and marketing restrictions on ultra-processed products; and promotion of fresh or minimally processed foods, should be considered part of important health policy to improve global public health.”
The report says it has been known for many years that eating a healthy, balanced diet reduces the risk of cardiovascular disease, as well as other diseases such as cancer. So, in a way, the results of these 2 studies should not come as a surprise.
Most healthy diets include plenty of fresh fruit and vegetables, and less sugar, salt and saturated fats. The studies, as expected, found people who ate lots of heavily processed food had a generally less healthy lifestyle. The researchers tried to take such factors into account.
The report says what counts as ultra-processed food has been questioned by other researchers, who have asked if it really represents a specific category with clear boundaries. Some researchers would argue it’s possible to eat a healthy diet that includes a high proportion of highly processed food, if you choose products carefully.
The researchers say they adjusted their models to look at this and found that nutritional quality of the food did not affect the outcome. It was the processing that made the difference. They suggest that a range of factors, including the processing itself, additives or even packaging, could make highly processed food less healthy than the equivalent food made by hand.
Both studies are observational so can’t establish causality, and there’s a possibility that some of the observed risks may be due to unmeasured confounding factors. Nevertheless, both studies took account of well-known lifestyle risk factors and markers of dietary quality, and the findings back up other research linking highly processed food with poor health.
As such, both research teams say policies that limit the proportion of ultra-processed foods in the diet and promote consumption of unprocessed or minimally processed foods are needed to improve global public health.
This view is supported by Australian researchers in a linked editorial, who say the dietary advice is relatively straightforward: eat less ultra-processed food and more unprocessed or minimally processed food. They say future research should explore associations between ultra-processed food and health harms in different populations around the world, and examine how harm occurs (for example by changing the gut microbiome in ways that could disturb energy balance).
In the meantime, policy makers “should shift their priorities away from food reformulation – which risks positioning ultra-processed food as a solution to dietary problems – towards a greater emphasis on promoting the availability, affordability, and accessibility of unprocessed or minimally processed foods,” they conclude.
Objective: To assess the prospective associations between consumption of ultra-processed foods and risk of cardiovascular diseases.
Design: Population based cohort study.
Setting: NutriNet-Santé cohort, France 2009-18.
Participants: 105 159 participants aged at least 18 years. Dietary intakes were collected using repeated 24 hour dietary records (5.7 for each participant on average), designed to register participants’ usual consumption of 3300 food items. These foods were categorised using the NOVA classification according to degree of processing.
Main outcome measures: Associations between intake of ultra-processed food and overall risk of cardiovascular, coronary heart, and cerebrovascular diseases assessed by multivariable Cox proportional hazard models adjusted for known risk factors.
Results: During a median follow-up of 5.2 years, intake of ultra-processed food was associated with a higher risk of overall cardiovascular disease (1409 cases; hazard ratio for an absolute increment of 10 in the percentage of ultra-processed foods in the diet 1.12 (95% confidence interval 1.05 to 1.20); P<0.001, 518 208 person years, incidence rates in high consumers of ultra-processed foods (fourth quarter) 277 per 100 000 person years, and in low consumers (first quarter) 242 per 100 000 person years), coronary heart disease risk (665 cases; hazard ratio 1.13 (1.02 to 1.24); P=0.02, 520 319 person years, incidence rates 124 and 109 per 100 000 person years, in the high and low consumers, respectively), and cerebrovascular disease risk (829 cases; hazard ratio 1.11 (1.01 to 1.21); P=0.02, 520 023 person years, incidence rates 163 and 144 per 100 000 person years, in high and low consumers, respectively). These results remained statistically significant after adjustment for several markers of the nutritional quality of the diet (saturated fatty acids, sodium and sugar intakes, dietary fibre, or a healthy dietary pattern derived by principal component analysis) and after a large range of sensitivity analyses.
Conclusions: In this large observational prospective study, higher consumption of ultra-processed foods was associated with higher risks of cardiovascular, coronary heart, and cerebrovascular diseases. These results need to be confirmed in other populations and settings, and causality remains to be established. Various factors in processing, such as nutritional composition of the final product, additives, contact materials, and neoformed contaminants might play a role in these associations, and further studies are needed to understand better the relative contributions. Meanwhile, public health authorities in several countries have recently started to promote unprocessed or minimally processed foods and to recommend limiting the consumption of ultra-processed foods.
Bernard Srour, Léopold K Fezeu, Emmanuelle Kesse-Guyot, Benjamin Allès, Caroline Méjean, Roland M Andrianasolo, Eloi Chazelas, Mélanie Deschasaux, Serge Hercberg,
Pilar Galan, Carlos A Monteiro, Chantal Julia, Mathilde Touvier
Objective: To evaluate the association between consumption of ultra-processed foods and all cause mortality.
Design: Prospective cohort study.
Setting: Seguimiento Universidad de Navarra (SUN) cohort of university graduates, Spain 1999-2018.
Participants: 19 899 participants (12 113 women and 7786 men) aged 20-91 years followed-up every two years between December 1999 and February 2014 for food and drink consumption, classified according to the degree of processing by the NOVA classification, and evaluated through a validated 136 item food frequency questionnaire.
Main outcome measure: Association between consumption of energy adjusted ultra-processed foods categorised into quarters (low, low-medium, medium-high, and high consumption) and all cause mortality, using multivariable Cox proportional hazard models.
Results: 335 deaths occurred during 200 432 persons years of follow-up. Participants in the highest quarter (high consumption) of ultra-processed foods consumption had a higher hazard for all cause mortality compared with those in the lowest quarter (multivariable adjusted hazard ratio 1.62, 95% confidence interval 1.13 to 2.33) with a significant dose-response relation (P for linear trend=0.005). For each additional serving of ultra-processed foods, all cause mortality relatively increased by 18% (adjusted hazard ratio 1.18, 95% confidence interval 1.05 to 1.33).
Conclusions: A higher consumption of ultra-processed foods (>4 servings daily) was independently associated with a 62% relatively increased hazard for all cause mortality. For each additional serving of ultra-processed food, all cause mortality increased by 18%.
Anaïs Rico-Campà, Miguel A Martínez-González, Ismael Alvarez-Alvarez, Raquel de Deus Mendonça, Carmen de la Fuente-Arrillaga, Clara Gómez-Donoso, Maira Bes-Rastrollo
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