Published on 1 March 2016

A harmful form of bacteria found in processed food like burgers and ready meals has led to a team of researchers calling for food producers to make food healthier.

A team from the University of Leicester have developed a new technique to identify harmful bacterial molecules in certain processed foods that are undetectable in non-processed and fresh foods.

Researchers suggested this could mean that the bacteria was developed during the manufacturing process.

Processed food has been found to contain more harmful bacteria than fresh foods

The study, recently published in the journal Nutrition, Metabolism and Cardiovascular Diseases, identified a particular kind of contaminating molecule known as ‘pathogen-associated molecular patterns’ (PAMPs), released by certain types of bacteria as they grow during some food processing and refrigeration processes.

Researchers believed that this bacteria could increase the risk of developing health conditions such as coronary artery disease and type 2 diabetes.
Dr Clett Erridge, from the University of Leicester’s Department of Cardiovascular Sciences who led the study, 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. Our recent findings have uncovered a potential mechanism by which certain types of processed food increase risk of developing these diseases.
“In essence, we have discovered that contaminating molecules that arise in processed foods from the overgrowth of a specific type of bacteria during refrigeration or food processing can cause our immune systems to over-react in a manner that might be damaging to health when we eat foods containing these molecules.”

As part of the study a group of volunteers were placed on a diet low in PAMPs for one week after which researchers discovered an 11% reduction in white blood cells and an 18% reduction in low-density lipoprotein (or LDL, also referred to as ‘bad’ cholesterol) – which if maintained would be equivalent to reducing the risk of developing coronary artery disease by more than 40%.

Bowl of soup.

In addition, participants in the study also reported weight loss (on average 0.6kg) and waist circumference (average 1.5 cm). Researchers believed that the reduction in waist size and white cell count could help reduce the risk of developing type 2 diabetes by more than 15%.

When the same volunteers ate a diet that was higher in PAMPs, the benefits were reversed, highlighting the negative effect PAMPs appear to have on the health of an individual.
Following their experimental study the researchers believed that their new method of detecting PAMPs could be used by food manufacturers to help identify at what point in their production process the PAMP molecules were developing in foodstuffs, such as which parts of machinery, or which raw materials introduce contamination to their products.

Dr Erridge said: “Crucially, we have found that some processed foods do not contain these molecules, and our results suggest it should be possible to manufacture almost any current foodstuff in a manner that results in a low content of pro-inflammatory PAMP molecules. Our method can also be used to monitor progress in efforts to clean up the production process.
“The present work suggests that removing these molecules from common foods could provide a health benefit to consumers and suggest a potential means of making some of our favourite foods healthier without any appreciable change to taste, texture, cost or ingredients.”

Among processed foods found to frequently contain high levels of PAMPs included foods containing minced meat (like sausages and burgers), ready meals (especially lasagne, bolognese), some cheeses, chocolate and some types of ready-chopped vegetables, such as onions.
Foods containing these as ingredients, including sauces and sandwiches, were also found to have a relatively high risk of PAMP contamination.
Researchers said their findings suggested that when food is absolutely fresh, including any type of meat, fruit or vegetable, it contains undetectable levels of PAMPs. However, once it has been chopped finely, especially if minced, the PAMP content rises rapidly, day on day, even when stored at refrigeration temperature.

Pam Dyson PhD RD, Research Dietitian at Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM) and author of the DRWF leaflet A healthy diet and diabetes, said: “There has been a lot of interest over the past few years about the role that bacteria play in maintaining health, and particular interest in the bacteria of the gut, also known as the microbiome. We all have trillions of bacteria in our small and large intestine, weighing about three pounds in total, and each individual has a unique bacterial profile which depends on a number of factors including genetic inheritance, diet and use of antibiotics. Recent research suggests that gut bacteria are implicated in a series of chronic diseases such as obesity, diabetes, cardiovascular disease and cancer, although how the microbiome influences these diseases is not yet clear. This present study attempts to identify the specific components of the diet that may affect metabolic health.

“The take-home message is that high PAMP foods (processed foods, particularly chilled ready meals containing minced meat or chopped onion) appear to increase the risk of metabolic disease and low PAMP foods (fresh, unprocessed foods) appear to reduce the risk. It is important to remember that this is a small study conducted with healthy volunteers and that larger, long-term studies will be needed to confirm these findings, and to explore the unexplained findings of significant reductions in LDL cholesterol and body weight.

“In the meantime, there can be no harm in avoiding large amounts of processed foods in order to reduce risk. The kind of foods recommended for health – vegetables, fruit, unprocessed and wholegrain carbohydrates, seafood, low fat dairy products and vegetable oils are naturally low in PAMP and can continue to be enjoyed as part of a healthful diet.”

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