Common food additives 'linked' to bowel cancer

NHS: "Why processed food may cause bowel cancer: Common additives change gut bacteria which allow tumours to grow," reports the Mail Online. This follows a study in mice investigating whether common food additives (E numbers) called emulsifiers cause inflammation in the gut that in turn triggers bowel cancer. The researchers divided the mice into three groups: two received emulsifiers, either sodium carboxymethycellulose (CMC) or polysorbate 80 (P80), and the third group received water. They also gave the mice toxins to trigger inflammation and cancer.

Overall, they found more and bigger cancerous tumours in mice given the emulsifiers, in addition to some inflammatory changes. It was suggested the reason could be that emulsifiers altered the balance of gut bacteria, creating an environment more favourable to the development of cancer.
But while these findings may be alarming, it's too early to say if they apply to humans. Findings of animal studies aren't directly transferable to humans. The mice were also given far greater doses of emulsifiers than a human would consume, in addition to toxins that cause inflammation and cancer.
It is well known that bowel cancer is linked to high levels of body fat and eating lots of processed meat, but the link with emulsifiers needs further research.
All food additives undergo a safety assessment before they can be used and it's not yet possible to say for certain whether any of these pose a risk of cancer in humans at the levels permitted.
The Food Standards Agency (FSA) has more information about additives and E numbers.

Where did the story come from?

The study was carried out by researchers from Georgia State University in Atlanta and was funded by a National Institutes of Health (NIH) grant.
The study was published in the peer-reviewed medical journal Cancer Research.
It has largely been reported accurately in the media, which for the most part did mention the limitations of the research.
The Sun provided a quote from Professor Sanders from Kings College London who said the mice were fed the E numbers at a level of 1%, described as: "a very high intake of the food additives compared to what might be found in human diets".
He added: "We can't assume this study is applicable to humans, so it shouldn't be cause for concern."
But some headlines oversimplified the research and implied that a definite link between additives and bowel cancer in humans had been found. Moreover, some of the coverage – for example, the story in the Daily Express – didn't mention the study's important limitations.

What kind of research was this?

This was an animal study in mice that aimed to see whether food additives (E numbers) called emulsifiers found in processed food could be responsible for bowel cancer.
Emulsifiers prevent foods from separating and give food body and texture. They're commonly found in food such as ice cream.
The researchers suggested that emulsifiers may cause low grade inflammation in the gut and increase levels of bad gut microbes, resulting in increased levels of cancer.
This kind of research is a valuable first step in understanding the processes by which emulsifiers may lead to inflammation in the gut, and then seeing whether this could be linked with cancer risk.
But this is early, animal based research and we can't be sure whether the findings would be the same in humans. 

What did the research involve?

The researchers split mice into three groups, with each group being given one of the following:

• sodium carboxymethycellulose (CMC) – a soft and lubricating "gum" found in products like ice cream and toothpaste
• polysorbate 80 (P80) – a thickening liquid, also found in things like ice creams and sauces to stop them separating
• water (control group)

The mice received these solutions for 13 weeks during which time they had their bodyweight measured and faeces collected on a weekly basis.
Following the 13 week period, the mice were given an injection of azoxymethane (AOM), a strong cancer-causing substance in rodents, to induce colon cancer. Five days later a dose of dextran sulfate sodium (DSS) used to induce colitis (inflammation of the lining of the colon).
Five days later they were given a dose of dextran sulfate sodium (DSS) used to induce colitis (inflammation of the lining of the colon).
At the end of the experiment, the mice were killed, and colon length, colon weight, spleen weight and body fatness were measured. Any cancerous tumours found were counted and measured.

What were the basic results?

The mice receiving CMC and P80 showed a small but significant increase in their body mass. The emulsifier treatment also impaired blood glucose regulation. This was evident from increased food consumption and poor fasting blood glucose levels.
All mice receiving AOM and DSS lost weight during DSS treatment. When examined after death they had features of inflammation, including increased colon and spleen weights.
The mice in the two groups given emulsifiers were found to have more inflammatory changes compared to mice in the control group. There was also increased tumour development in the mice that consumed emulsifiers in comparison to the control group.
Further exploration suggested that the greater inflammatory changes and cancer development in the emulsifier groups were caused by these substances altering the balance of gut bacteria.

How did the researchers interpret the results?

The researchers conclude: "We found that emulsifier induced alterations in the microbiome were necessary and sufficient to drive alterations in major proliferation and apotosis [cell death] signalling pathways thought to govern tumour development."
"Overall, our findings support the concept that perturbations in host-microbiota interactions that cause low-grade gut inflammation can promote colon carcinogenesis [tumour formation]."

Conclusion

This animal study aimed to investigate whether additives called emulsifiers promote inflammation that in turn triggers cancer.
The findings suggest emulsifiers could lead to greater inflammation and bowel cancer in mice, and this may be caused by them altering the balance of gut bacteria. But there are important limitations to note:

• The mice were fed large doses of the substances not comparable to the levels found in food humans would eat.
• The mice were also given strong drugs both to cause cancer and trigger bowel inflammation. Without these substances, the emulsifiers alone may have had minimal effect.
• Findings of animal studies aren't directly transferable to the effect that may be seen in humans consuming food products containing emulsifiers. Human studies would be needed to confirm these findings. For example, researchers could analyse the effect of directly adding emulsifiers to bowel tissue samples in the laboratory.
• It's difficult to understand the biological processes that may be behind the increased cancer development in mice exposed to emulsifiers. For example, they may be due to increased weight gain or poor glucose control, rather than the substances being the direct cause.

It's too early to apply these findings to humans. While it's well known that bowel cancer is linked to high levels of body fat and higher consumption of processed meats, the link with emulsifiers is one that needs to be researched further.