People who eat more ultra-processed foods (UPF) are at increased risk of developing type 2 diabetes, but this risk can be lowered by consuming less processed foods instead, finds a new study led by researchers at UCL.
The study, published in The Lancet Regional Health - Europe in collaboration with experts at the University of Cambridge and Imperial College London, investigated the relationship between the degree of food processing and type 2 diabetes risk, including which kinds of UPF were most high-risk.
The team analysed UPF intake and health outcomes for 311,892 individuals from eight European countries over 10.9 years on average, during which time 14,236 people developed type 2 diabetes.
They found that every 10% increase in the amount of ultra-processed foods in a person's diet is linked with a 17% increase in type 2 diabetes risk, but this risk can be lowered by consuming less-processed foods instead.
The highest risk UPF groups were savoury snacks, animal-based products such as processed meats, ready meals, and sugar-sweetened and artificially-sweetened beverages, suggesting that particular attention should be paid to these foods to help tackle ill-health.
The degree of processing in foods is most often assessed using the Nova classification, which divides foods into four groups: unprocessed or minimally processed foods (MPF) such as eggs, milk, and fruit; processed culinary ingredients (PCI) such as salt, butter and oil; processed foods (PF) like tinned fish, beer and cheese; and ultra-processed foods such as ready-to-eat/heat mixed dishes, savoury snacks, sweets and desserts.
The exact causes of the link between UPF and type 2 diabetes are unconfirmed, though several factors are thought to be at play including overconsumption and weight gain. In a previous study, backed up by new analysis in this study, increased body fat accounted for around half the association.
Samuel Dicken, first author of the study from UCL Division of Medicine, said: "We know that ultra-processed foods are associated with a higher risk of certain diseases such as type 2 diabetes. As expected, our findings confirm this link and show that every 10% increase in the diet from UPF increases the risk of developing type 2 diabetes considerably.
"Most studies to date only consider UPF as a whole, but we also suspect that there may be different risks associated with different types of UPF, and the risks of other processing groups have not been well researched. Our analysis goes a step further than previous studies, by looking at all four processing groups in the Nova classification to gauge the impact on type 2 diabetes risk when we substitute UPF with less processed foods, as well as looking at nine UPF subgroups.
"The good news is that replacing UPF with less processed foods was associated with a reduced type 2 diabetes risk."
In the study, researchers from UCL analysed data from the EPIC study, which has investigated the relationship between diet, lifestyle, and environmental factors, and the incidence of chronic diseases in more than half a million Europeans over time.
Additional analysis on the data was performed to separate UPF into nine subgroups1 in order to better understand how level of processing affects type 2 diabetes risk.
Alongside analysing how eating UPF affected a person's risk of developing type 2 diabetes, the researchers performed substitution modelling on the data to see how, theoretically, replacing one Nova food group with another would affect type 2 diabetes risk.
The results showed that substituting 10% of UPF in the diet with 10% of MPF/PCI reduced type 2 diabetes risk by 14%.
Substituting 10% of UPF in the diet with 10% of PF reduced diabetes risk by 18%. The authors say this may be down to the fact that 30-50% of PF intake in this study came from beer and wine, which have been associated with a lower risk of type 2 diabetes in a previous EPIC study. PF also includes salted nuts, artisanal breads, and preserved fruits and vegetables.
Analysis of the nine UPF subgroups showed that savoury snacks, animal-based products, ready meals, and sugar-sweetened and artificially-sweetened beverages were associated with higher incidence of type 2 diabetes.
High proportions of these less healthy foods contributed to overall type 2 diabetes risk. In the top 25% of UPF consumers, where UPF made up 23.5% of their total diet, sweetened beverages alone accounted for nearly 40% of their UPF intake and 9% of their diet overall.
However, UPF breads, biscuits and breakfast cereals, sweets and desserts, and plant-based alternatives were associated with lower incidence of type 2 diabetes.
Professor Rachel Batterham, senior author of the study from UCL Division of Medicine, said: "The UPF subgroup analysis in this study has been revealing and confirms that not all foods categorised as UPF are alike in terms of the health risks associated with them.
"Breads and cereals, for example, are a staple of many people's diets. Based on our results, I think we should treat them differently to savoury snacks or sugary drinks in terms of the dietary advice we provide."
The authors say that, due to the observational nature of the study, it can only measure associations rather than causal effects.
The UCL team are currently conducting a trial to assess the impact of UPF versus MPF diets meeting healthy diet guidance, which will further clarify the results of this study. The results of this trial are expected to be published in 2025.
In 2023, the UK Scientific Advisory Committee on Nutrition (SACN) reviewed the available scientific evidence on UPFs and published a report stating that increased consumption of processed foods, particularly UPFs, was associated with an increased risk of health issues such as obesity, chronic diseases like type 2 diabetes, and depression. The report also highlighted the need for additional research to understand the cause of these associations.
Professor Marc Gunter, an author of the study from Imperial College London and one of the coordinators of the EPIC study, said: "The findings from this study add to the growing body of research that links consumption of UPF with higher risk of certain chronic diseases including obesity, cardiometabolic diseases and some cancers. While such a study cannot determine causal relationships, it does suggest that reducing consumption of some UPF and replacing them with unprocessed, whole foods, might lower risk of type 2 diabetes. Further research to understand mechanisms and potential causal pathways is now needed."
