Two distinct patterns of molecules in the blood linked to an ultra-processed diet and a minimally processed diet have been identified in a new study by UCL and Imperial College London researchers. The finding builds on research into how the extent of food processing may itself create harmful health outcomes over time. 

The study, published in the journal BMC Medicine, involved data from more than 6,000 adults in the UK who had blood tests and filled in questionnaires about their diet and whose health was then tracked for up 20 years.

The researchers looked at patterns of metabolites – tiny molecules the body makes as it processes food and carries out other chemical reactions. They measured 233 metabolites in the blood and used machine learning to identify the metabolites most strongly linked to each diet.

They found that molecules linked to the ultra-processed diet included more unhealthy fats and lower levels of healthy fats such as omega-3 fatty acids, while a minimally processed diet had the opposite pattern.

The team also found that this biological signature accounted for up to half (43% to 51%) of the link between diet and a person’s risk of developing heart disease and type 2 diabetes. This link to disease remained even after accounting for the higher levels of sugar, fat and salt present in the ultra-processed diets studied.

Lead author Dr Eunice Wang, who carried out the work while a PhD student at UCL Epidemiology & Public Health, said: “We know there is a link between ultra-processed food and disease, but there is uncertainty over what is driving this connection – whether it is due to higher levels of sugar, salt and saturated fat, as well as dense calorie content, or whether the risks also come from food processing. Our findings hint that processing itself may play a role, although more research is needed to support this.”

“We know there is a link between ultra-processed food and disease, but there is uncertainty over what is driving this connection …. Our findings hint that processing itself may play a role, although more research is needed to support this”

The UK’s Scientific Advisory Committee on Nutrition (SACN), the independent committee that advises the government, is currently weighing evidence on the health impact of ultra-processed foods.

Senior author Professor Clare Llewellyn (UCL Behavioural Science and Health) said: “Current UK dietary guidance does not consider processing itself as a risk but recommends a reduced intake of foods high in ingredients such as sugar, salt and saturated fat.

“This study, which is the first to compare metabolic signatures of ultra processed and minimally processed diets, adds to the evidence needed to inform future policy discussions about whether the degree of processing should be considered alongside nutritional profile, when assessing the 

Among study limitations, the researchers noted that, as it was an observational study, it could not determine cause and effect. Study strengths included longer follow-up of participants compared to other, similar studies.