Bacterial Products In Processed Foods May Increase Disease Risk

Love the easiness of pre-chopped vegetables and ready meals? You might want to think twice before buying them as new research points out that eating processed foods may increase your risk for heart disease. 

What's new?

In a paper published in the professional journal Nutrition, Metabolism and Cardiovascular Diseases researchers from the University of Leicester report that people on a diet low in bacterial products known as PAMPs have reduced levels of LDL and lose weight. These PAMPs or ‘Pathogen-Associated Molecular Patterns’ are molecules found in many pathogens (for example cell wall parts of bacteria) that are specifically recognized by the human immune system. When the immune system encounters a PAMP it sends out an alarm warning that the host may be under attack by pathogens. These PAMPs are found in many processed food stuffs such as ready meals, prepackaged sandwiches, cheese, chocolates, prepackaged chopped vegetables and minced meat stored at refrigerator temperatures. Bacteria introduced during processing grow and produce PAMPs during the refrigeration process. In contrast PAMPs are undetectable in fresh foods such as intact steaks and vegetables. For example, previous research has found that the level of bacteria in onions increase about 30-fold immediately after factory slicing and after a short period of refrigeration bacterial levels can reach approximately 100 million per gram. 

Minced meat is high in PAMPs

Does avoiding PAMPs improve health?

The researchers recruited 11 healthy male volunteers, who prior to this study had a diet high in PAMPs, and asked them to avoid foods high in PAMPs for a week and observed a reduction in LDL cholesterol of 18%. Furthermore, the volunteers had a 12% reduction in their white cell count (indicating less exposure to bacteria or bacterial-products), a reduction of body weight of 0.7 kg and a reduced waist circumference of on average 1.6 cm. Later the researchers switched the volunteers for 4 days to a high PAMP diet (containing about 1500 kCal) and this resulted in an increase in LDL cholesterol, white blood cell count (+14%) and an increase in waist circumference of 1.2 cm. No changes in CRP and insulin sensitivity were found. It should be pointed out that the intake of saturated fat was about 75% higher in the high PAMP diet compared to the low PAMP one. This together with likely differences in the amount of food additives between the two diets make the interpretation of these data difficult. Therefore the researchers set up a second experiment. It should be pointed out however that the higher content of saturated fat in the high PAMP diet was unlikely to explain the higher LDL levels in people consuming this diet as previous dietary studies have found only small effects of saturated fat on LDL over prolonged periods of time. 

Are whole vegetables superior?

In the second experiment 13 healthy male volunteers were provided with an onion-based breakfast. The study was blinded on the participant’s side. The low PAMP meal contained 200 grams of freshly chopped onions while the high PAMP diet consisted of 200 grams of ready-chopped onions, stored at refrigeration temperature and consumed on the ‘best before date’. The onions were coated in batter and deep fried. The high PAMP diet contained about an approximately 35-fold higher amount of PAMPs than the low PAMP diet. The white blood cell count was significantly reduced 24 hours after the consumption of the low PAMP diet. After a two week washout period the same volunteers were switched to the high PAMP onion breakfast followed by a low PAMP diet for the rest of the day. At the end of the day the white blood cell count was increased. 

Don't we have lots of bacteria in us already?

Given the large bacterial content of the human gut, recent estimates point out that the number of gut bacteria are equal to the number of human cells (http://dx.doi.org/10.1101/036103), it is surprising that bacterial products from the food would have any influence. But analysis of the amount of PAMPs in fecal matter find only low levels. Presumably few bacterial species present in the gut produce soluble PAMPs.  

In conclusion we can say that diets high in bacterial-products may have negative health effects. However, more research will be needed to confirm these results and to further explore the the ways in which dietary PAMPs may influence multiple biological processes in the body.  

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