According to the researchers, processed food contain high levels of bacterial molecules known as ‘pathogen-associated molecular patterns’ (PAMPs) which may increase the risk of conditions such as coronary artery disease and type 2 diabetes.
They also found that PAMPs were undetectable in fresh foods, but abundant in junk food and processed foods like ready-chopped vegetables, onions, pasta sauces and sandwiches, suggesting that they grow during the manufacturing process, when food is chopped and refrigerated.
Lead researcher Dr Clett Erridge, of the University of Leicester, said: 'It has been understood for many years that frequent consumption of highly processed foods, particularly processed meats, is associated with increased risk of developing a range of diseases, including cardiovascular disease, type 2 diabetes and obesity.'
"PAMPs can cause our immune systems to over-react in a manner that might be damaging to health when we eat foods containing these molecules," he said.
During the research, volunteers who ate a diet low in PAMPs for a week had their white blood cell (WBC) reduced by 11 per cent and their 'bad' LDL cholesterol levels reduced by 18 per cent.
Scientists hope this new knowledge will help food manufacturers in removing the molecules from food, making them healthier without changing the taste, texture, cost or ingredients.
The study was published in the journal Nutrition, Metabolism and Cardiovascular Diseases.