Ultra-processed food: linked to ill health, but why?

Diets high in ultra-processed food are linked to a higher risk of conditions such as obesity, type 2 diabetes and heart disease, the NHS says. It is not known if that is down to the processing or to the calories, fat, salt and sugar these foods contain.

The NHS lists sweetened drinks, crisps, packaged cakes and biscuits, ice cream, sweets and chocolate, some ready meals and packaged meat pastries like pies and pasties as examples. There is no single, universally agreed definition, the Food Standards Agency says.

The research includes a 2024 review in the BMJ of earlier meta-analyses, which counted 45 pooled results covering almost 10 million participants. Another is a 2019 study by the US National Institutes of Health, in which 20 adults spent two weeks on each of two diets, one ultra-processed and one unprocessed. A third is an April 2025 update from the Scientific Advisory Committee on Nutrition (SACN). What they found:

• The BMJ review found links between ultra-processed food and 32 of the health measures it checked, including death from heart and blood vessel disease, type 2 diabetes and anxiety. It rated the evidence behind 41 of its 45 pooled results as low or very low quality.
• SACN said most newer reviews associated eating more ultra-processed food with higher risks of outcomes such as obesity, type 2 diabetes, heart and blood vessel disease, cancer and mental health conditions.
• SACN said analyses suggest foods based on meat and animal products, and sweetened drinks, tend to be linked with higher risk, while vegetarian alternatives were not. Results for bread and cereals, savoury snacks, dairy products and several other groups were mixed.
• In the US study, the adults ate about 508 calories a day more on the ultra-processed diet. They gained 0.9kg on it and lost 0.9kg on the unprocessed diet.
• SACN identified one small randomised trial, of nine people, in which participants gained more weight (1.1kg) on an ultra-processed diet than on a diet without such foods.

SACN said the evidence is almost exclusively observational, and even after adjustments some confounding – factors related to both ultra-processed food consumption and the health outcomes – is likely to remain.

SACN has said more research is needed before it can draw any firm conclusions about whether these foods cause poor health, the Food Standards Agency says.

Some ultra-processed foods can be included in a healthy diet, the NHS says, such as wholemeal sliced bread, wholegrain or higher fibre breakfast cereals or baked beans. It says most people would probably benefit from eating less of those high in saturated fat, salt or sugar. Anyone worried about their weight can ask a GP or a dietitian for advice, the NHS says.