Scientists look at what puts the 'junk' into junk foods

"Scientists say they have cracked what makes processed foods… harmful,"  the Daily Mail reports. A small study suggests that processed foods that are high in "PAMPs" – pathogen-associated molecular patterns – may trigger inflammation inside the body.

PAMPs are molecules that are associated with infectious bacteria, so in the same way as an infection, they can trigger an immune response in the way of inflammation. And some experts suspect that prolonged inflammation can increase the risk of chronic diseases such as high blood pressure and type 2 diabetes.

This new study attempted to assess the relative benefits of a high-PAMP diet compared to a low-PAMP diet on a number of biomarkers associated with immune response.

The study, involving 24 healthy men over 11 days, tentatively suggested that PAMPs did act to trigger some biomarkers linked to an immune response – although the results weren't consistent.

Due to the size and shortness of the study its immediate implications are unclear.

There are also other limitations to consider. For example, the study didn't measure new cases of diabetes or cardiovascular disease, or any disease.

The assumption that the signs of raised inflammation seen in those given a high-PAMP diet are big enough to cause disease in the future is currently unproven.

The results of this study are intriguing, but represent points of interest for further study, not established facts or guidance.

Processed foods often have a high salt, sugar and fat content, so it is not a good idea to let them become a staple of your diet.

Where did the story come from?

The study was carried out by researchers from the University of Leicester (England) and was funded by University of Leicester Campbell Immunology Fund and the Higher Committee for Education Development in Iraq.

The study was published in the peer-reviewed medical journal Nutrition, Metabolism & Cardiovascular Diseases.

The Daily Mail's headline "Scientists say they have cracked what makes processed foods like burgers and ready meals harmful", seems to imply that the reason processed foods are unhealthy is some sort of mystery.

This downplays the many existing reasons why foods like burgers and ready meals are bad for your health; they are called "junk food" after all. Many ready meals contain lots of added sugar and salt to make them taste better, and can be high in fat. The fat and sugar can contribute to weight gain, which in turn increases your risk of many diseases.

A high-salt diet can raise your blood pressure, which elevates your risk of heart attacks and strokes. 

The added issue is that you might not be aware of the high levels of fat, salt and sugar in the foods, as not everyone pays attention to food labels.

This means you might be consuming levels likely to be harmful to health in the long run and not even know.

What kind of research was this?

This small study looked at the effects of dietary PAMPs on indicators of inflammation in a small group of healthy adult men over the course of just over a week.

Small and short studies like this do not set out to provide solid answers, or provide weighty proof. Instead they attempt to scratch the surface of a new research area, present new theories and kick up questions that bigger and better studies might be able to answer. As such, the results represent points of interest for further study, rather than established facts.

What did the research involve?

The research had two main parts.

The first part fed 11 healthy adult men (average age 38) two high-PAMP meals a day for four consecutive days while testing their blood before and after for signs of immune response changes. For the seven days before all men received diet advice to eat lower PAMP. This was because most men regularly consumed high-PAMP diets outside of the study so the researcher wanted to get everyone to a lower starting point. The rationale is that the impact of PAMP levels going from high to very high might be harder to detect than if it went from low to high. The men filled in food diaries to see if they were taking the advice.

The second part fed a group of 13 different healthy men (average age 28) onion bhajis made from freshly chopped onion and monitored the impact on blood inflammation measures for 24 hours. Two weeks of normal eating passed before the same men were asked to eat a nutritionally identical meal made from pre-chopped onions – high in PAMPs.

Any changes in weight circumference, blood cholesterol and blood fats were also measured.

What were the basic results?

The study team found that PAMPs were high in many processed foods such as lasagne and spaghetti bolognese ready meals, as well as baked pies, pasties and rolls.

Encouraging men to follow a low-PAMP diet for seven days appeared to reduce some signs of inflammation (their white blood cell count reduced by 12%), lowered their cholesterol (-0.69 mmol/l), and they managed to lose weight (-0.7kg), including averaging 1.6cm less around the waist. Their insulin sensitivity – as risk factor for diabetes – was unaffected. The four-day high-PAMP diet largely reversed these effects, expect the weight loss, which didn't fully return to starting levels. For example, the white blood cell count went back up by 14% and men put back around 1.2cm around their waists.

The study of nutritionally identical foods, differing only in their PAMP levels, showed high-PAMP foods made little difference to inflammatory markers 24 hours after eating. There were, however, signs the low-PAMP foods lowered inflammatory markers, for example, there were fewer white blood cells.

How did the researchers interpret the results?

The study team concluded that: "A low-PAMP diet is associated with reduced levels of several cardiometabolic risk factors, while a high-PAMP diet reverses these effects. These findings suggest a novel potential mechanistic explanation for the observed association between processed food consumption and risk of cardiometabolic diseases."

Conclusion

This small study tentatively suggests that processed foods high in PAMPs act to trigger an immune response in people that ultimately may raise the risks of type 2 diabetes and cardiovascular disease later in life.

At present these conclusions are very shaky. The study was small (just 24 healthy men took part) and short term (11 days), so gives us only the first loose threads of evidence about what's going on, rather than a more solid, clear picture.

For example, the study didn't measure new cases of diabetes or cardiovascular disease, or any disease. The link to disease rests on the assumption that the raised levels of inflammation seen in those given a high-PAMP diet will be big enough to cause disease in the future. This could be right or wrong, and needs testing to see if it holds true.

The first part of the study was also not controlled for other foods, which probably biased the results. The second part was much more controlled, and found very little immune impact after a high-PAMP meal – at least over 24 hours. More changes happened in the low-PAMP scenario.

The weight change might also be a red herring. It's not surprising that men who ate lots of junk food before the study lost a bit of weight after a week following advice to eat healthier (less than 1% of their body weights overall). But we certainly can't pin this weight change on the PAMPs, there were far too many other variables involved.

The results of this study are intriguing and represent points of interest for further study, not established facts.

Hopefully a larger study will follow to look further at this issue.