High-fibre diet positively influences blood values

When PhD candidate Paul Gill began his biomedical science course at Monash University he had no idea his studies would immerse him in one of the most dynamic fields of contemporary science: the gut microbiome.

Paul’s first paper, recently published in The European Journal of Nutrition, highlighted the potential of dietary fibre therapy to manipulate the production of short chain fatty acids (SCFA) and blood plasma concentrations. SCFAs are a group of organic acids produced in the gut from the bacterial fermentation of fibre in fruit, vegetables and certain grains. They are important for gut health but then absorbed into the bloodstream.

The study, co-led by the Department of Gastroenterology’s Professor Peter Gibson and Dr Jane Muir, was designed to find out whether the scientists could use diet to change SCFAs in the blood, and whether this change could also have a meaningful effect on the human immune system.

Based on work Paul conducted during his Honours year in 2015, it aimed to replicate in humans, studies in animal models led by Professor Charles Mackay at Monash Clayton which found that SCFAs offered protection from inflammatory diseases such as allergies, asthma and from type 1 diabetes.

Designed as a pilot to a larger investigation, the study asked 10 participants to adhere to a carefully controlled high-fibre diet over five days then measured SCFA levels in the blood and compared them after the same participants followed a low-fibre diet over five days.

“We found a big increase in the circulating SCFAs acetate and propionate in the blood after the high-fibre diet as compared to the low-fibre diet,” Paul said. “That was a reproducible result from what we were finding in animal models so we were pretty happy with that,” he said. “It’s really good evidence to show that what you eat can alter your gut bacteria and come out in your blood.”

The multi-disciplinary investigation was an eye-opener for Paul.

The meals were cooked at Monash University’s Nutrition and Dietetics at Notting Hill by research chef Ms Trish Veitch, frozen, then delivered by Paul to the participants. Analytical chemist Dr Bruce May from the CSIRO in Adelaide taught Paul how to undertake the SCFA analysis. Co-supervisor immunologist Professor Menno van Zelm and Associate Professor Rosemary Ffrench, assisted him with the flow cytometry analysis.

“I came into the study with knowledge of immunology and had done a bit of work in animal models. When I had the opportunity to potentially look at it in humans I thought ‘wow, that’s really exciting’,” he said. “Coming from immunology to gastroenterology in human research running a dietary intervention study there was a lot of logistics you need to be aware of – even delivering the food to people, you don’t expect to be doing that. It was a hectic year.

“It gave me an incredible level of confidence to know I could do these sorts of things.”

Dr Muir said that this was exciting work by Paul.

“It highlights the importance of different disciplines working together. Here we have nutrition science, gastroenterology and immunology all working to understand how dietary factors may influence and modulate the immune cells in humans,” she said.

The study did not find evidence, however, of changes in the immune system, tested by measuring levels of immune T-regulatory cells and a panel of cytokines, possibly because the five-day dietary intervention was too short, it said.

Paul is now analysing data from a larger version of the pilot study with 20 participants conducted over a three-week period which investigated a wider panel of immune cells.

“Once the results of that study are out we should have a good idea of how powerful this dietary approach is to change immune cells in the blood of humans,” he said.

Gill PA, van Zelm MC, Ffrench RA, Muir JG, Gibson PR. Successful elevation of circulating acetate and propionate by dietary modulation does not alter T-regulatory cell or cytokine profiles in healthy humans: a pilot study. Eur J Nutr. 2019 Oct 24. doi: 10.1007/s00394-019-02113-2. [Epub ahead of print]