‘Tip of the iceberg’: What NZ scientists just discovered about fruit, veges and gut health

Kiwi researchers have taken an important leap toward learning how fruit and vegetables may protect against inflammatory bowel diseases that affect millions of people around the world. Photo / 123RF

Kiwi researchers have taken an important leap toward learning how fruit and vegetables may protect against inflammatory bowel diseases that affect millions of people around the world.

Their newly published findings have suggested how compounds derived from fruit and veges can positively influence gut health, in what’s been described as a “tip of the iceberg” for further investigation.

“It’s a significant step towards understanding and potentially developing dietary strategies to manage inflammatory bowel diseases,” said the new study’s lead author, Malaghan Institute senior research fellow Dr Jeffry Tang.

These diseases – known to afflict more than 20,000 people in New Zealand alone – typically involve chronic inflammation of the gastrointestinal tract, with immune cells in the gut often behind them.

A healthy immune system in the gut needs to strike a delicate balance, by being active enough to combat infectious diseases, but not so aggressive that it triggers inflammation in intestinal cells.

This equilibrium is achieved by various immune cells: Some amplify immune responses, while others foster tolerance to the diverse stimuli within the gut.

With inflammatory bowel diseases, this balance is tipped so the immune system overreacts.

“Diets rich in fruit and vegetable are believed to help maintain a healthy intestine and be especially beneficial for people with inflammatory bowel disease,” Tang said.

“What we don’t exactly know is why. Why are fruits and vegetables good for immune balance? This is a black box we have to unpackage.”

With this novel study, Tang and his team have started to answer these questions, building the bridge between nutritional immunology and chemistry.

Previous studies looking at individuals with ulcerative colitis, a type of inflammatory bowel disease, have found that their CD4+ T-cells, a distinct population of immune cells, have an altered expression of a molecule called G Protein-Coupled Receptor 15 (GPR15).

The role of GPR15 was to help CD4+ T-cells migrate from the blood to the gastrointestinal tract, suggesting that modulating its expression could have some therapeutic benefit for inflammatory bowel diseases.

“We found this really interesting because we have been examining another molecule called the aryl hydrocarbon receptor (AhR) which seems to control GPR15 expression,” Tang said.

“While it was known that active compounds from fruits and vegetables can interact with AhR, it was unclear whether this can translate to the regulation of GPR15 expression, particularly in CD4+ T-cells.”

This prompted the team to explore whether the well-documented health benefits of eating fruits and vegetables might be linked to their role in directing beneficial immune cells to the gut through GPR15, while redirecting inflammatory cells away from it.

“We studied specific compounds derived from eating fruits and vegetables, namely polyphenol and glucosinolate metabolites,” Tang said.

“We showed they can indeed modulate AhR activity and GPR15 expression in CD4+ T cells.”

The findings, published in the Journal of Nutritional Biochemistry, suggest that the interaction of dietary compounds with AhR might control the migration of immune cells towards the gut and thereby dampen local inflammation.

“Our study points to specific compounds derived from eating fruit and vegetables that may positively affect immune balance,” Tang said.

“This is only the tip of the iceberg but it’s a step forward in uncovering the intricate ways in which dietary compounds might influence our gut health.”