Does broccoli aid gut problems?

"Eating broccoli and plantain could reduce bouts of Crohn’s disease,” reported The Daily Telegraph . It said researchers have found that certain types of soluble fibre from these plants can help to prevent bacteria from sticking to the gut's walls, thereby limiting the progress of the disease.

This study looked at whether fibres from various edible plants affected the transport of E. coli bacteria across specialised cells found in the lining of the bowel. The researchers also looked at whether substances called emulsifiers (commonly found in processed foods) altered the transfer of bacteria across these cells.

They found that fibres from broccoli and plantain reduced the transmission of bacteria across cells by between 45% and 82%, while leek and apple fibres had no effect. One emulsifier, called polysorbate 80, seemed to increase the transmission of bacteria across these cells.

This preliminary laboratory study has not shown that eating broccoli or plantain reduces attacks of Crohn’s and the findings have no immediate implications for the prevention or treatment of the disease. Nevertheless, these early findings are of scientific interest and may lead the way to clinical trials investigating whether certain plant foods and dietary modifications could have an effect on disease activity in people with Crohn’s.

Where did the story come from?

The study was carried out by researchers from the University of Liverpool, Linkoping university, Sweden, the University of Aberdeen and Provexis Plc (a company that makes medical dietary supplements and products and that provided the plant preparations used in the study). It was funded by the Wellcome Trust, the National Institute for Health Research, the National Association for Colitis and Crohn’s Disease, the Medical Research Council and the Swedish Research Council. It was published in the peer-reviewed medical journal Gut .

Both the BBC and The Daily Telegraph correctly reported that this was a laboratory study. However their headlines (“Broccoli boosts healthy gut” – BBC) did not clarify the fact that this research used extracts of the vegetable in a laboratory-based setting rather than testing broccoli consumption in people.

What kind of research was this?

Crohn’s disease is a chronic (long-term) condition where there is inflammation of the lining of the digestive system. Inflammation can occur anywhere in the digestive system, from the mouth to the anus (back passage). Common signs and symptoms include pain and diarrhoea (often with blood and mucus) while other effects on the body include weight loss, skin problems and arthritis.

Genetic factors are known to play a role in the development of the disease, but environmental factors may also contribute, such as diet and bacteria present in the gut. This laboratory research aimed to look at whether the uptake of bacteria by gut cells from people with Crohn’s was affected by certain plant soluble fibres from foods as well as substances found in processed foods.

There is a high prevalence of Crohn’s disease in developed countries where the typical diet is low in fibre and high in processed food. The researchers also point out that parts of the world, such as Africa, India and Central America, where plantains are a dietary staple, have low rates of inflammatory bowel disease as well as colon cancer. Therefore diet could be having an impact on Crohn’s disease.

There is a theory that the immune system in an individual with Crohn’s could "overreact" to certain food substances and microorganisms that may be present in the gut. In the lining of the gut there are specialised cells called "membranous" or "microfold" cells (M-cells). These are involved in the transport of proteins and micro-organisms through the bowel wall to the underlying lymph tissue and lymphoid follicles (Peyer’s patches), which are part of the immune system.

Previous studies in people with Crohn’s have noted that they have greater amounts of E. coli bacteria in their gut tissue, and that these E. coli often have special characteristics which make them more able to stick to, invade and live in gut wall cells. These are called adherent invasive E. coli (AIEC) strains. It is possible that bacteria such as E. coli could cause a heightened immune response in people with Crohn’s and be involved in the development of the disease. It is also thought possible that dietary factors could be involved – either by substances in the diet directly causing an immune response, or by affecting the transport of gut bacteria through these M-cells. That M-cells and the underlying Peyer’s patches may have some role in the development of Crohn’s disease is further supported by the fact that the early inflammatory lesions of Crohn’s have been found to lie over these cells.

This laboratory study set out to investigate whether certain soluble plant fibres from foods, as well as substances found in processed foods, have any effect on the transmission of the bacteria across these cells.

What did the research involve?

The laboratory research used strains of E. coli that had been isolated from six people with Crohn’s, as well as five control samples from people without Crohn’s. The plant-based sources of dietary fibre they tested were prepared from broccoli, leek, apple and plantain (a member of the banana family usually cooked as a vegetable). They also included two common food emulsifiers used in processed foods.

The researchers took human colon cells and grew them in the laboratory in conditions which encouraged them to develop into M-cells. They tested these cells to make sure that they could successfully transport bacteria, to show that they had developed into M-cells.

They then carried out a number of tests on the M-cells and the "parent" colon cells that they had been grown from. The cells were grown as a layer a single cell thick in special containers in such a way that the cell layers had solutions above and below them that did not mix. The researchers then applied bacteria to the upper surface of this layer and incubated it for up to four hours. After this time they tested to see how much bacteria had been transported across the cells to reach the solution underneath the cell layer. They then tested the effects of the different preparations on the transmission of E. coli across the cell layers. They applied the soluble fibre or other food substance onto the cells before applying the bacteria and measured whether this affected the transport of E. coli across the cell layer. They also tested the effect of the same substances on E. coli transport across normal tissue samples taken from the intestines of people without Crohn’s. They then analysed all the data, using validated statistical methods.

What were the basic results?

As the researchers expected, more E. coli was transported across the layers of specialised M-cells than across the layers of the "parent" human colon cells. The difference in transport across M-cells and the parent colon cells was greater when they used AIEC stains of E. coli from people with Crohn’s disease than when they used E. coli from people without Crohn’s disease.

They also found that:

• Both the preparations of plantain and broccoli markedly reduced the transport of E. coli across these specialised M-cells (range 45.3-82.6%).
• Apple and leek preparations had no significant effect on E. coli transport across the M-cells.
• One of the emulsifiers called polysorbate-80, increased E. coli transport across the cells, particularly the non-specialised colon cells.
• The plantain extract also reduced E. coli transport across the normal human intestine tissue samples, and polysorbate-80 increased transport across this tissue.

How did the researchers interpret the results?

The researchers say that transport of E coli across M-cells is reduced by soluble plant fibres such as plantain and broccoli, but increased by the emulsifier polysorbate 80. They suggest that fibre supplementation might protect against Crohn’s disease relapse by preventing bacterial invasion of intestinal mucosa, and that the effect of the food emulsifier could explain why Crohn’s rates are higher in developed countries where processed foods are common.

Conclusion

This carefully conducted laboratory study indicates that soluble fibres from certain plant foods can reduce the transport of E coli strains associated with Crohn’s, and their transfer across specialised cells of the bowel lining. It also shows that one emulsifier used in food processing has the opposite effect, by increasing transport.

This is early research aimed at furthering our understanding of how dietary and environmental factors might have a role in the development of Crohn’s. However, the findings have no current implications for the prevention or treatment of the disease, and it cannot be concluded from this study alone that any of these substances affect the development of Crohn’s. The study has not shown that eating broccoli or plantain reduces disease activity in Crohn’s. Even if there was an effect, it is unclear how much broccoli or plantain might be effective, or whether effective supplements of these substances could be developed.

These early findings are nevertheless of interest and may lead the way into later clinical trials investigating whether certain plant foods and dietary modifications could have an effect on disease activity in people with Crohn’s.