A diet low in fibre could lead to high blood pressure, which affects about one in three Australian adults and is one of the most significant risk factors for cardiovascular disease.
Just as a low-fibre diet can cause high blood pressure, a high-fibre diet can help to prevent it. Credit:Getty
A Monash University-led study published in the journal Circulation, found that mice given a diet either high or low in fibre exhibited different blood pressure patterns, possibly due to fibre's effect on gut bacteria.
Those fed the low-fibre diet developed high blood pressure while the others did not. The researchers then looked at the animals’ gut microbiota – the types of bacteria in their gut – and found the microbiome of the mice on a low-fibre diet became “completely different”.
Finally, they transferred gut bacteria from the high and low-fibre mice to germ-free mice, which had born and bred inside an isolator so they did not have their own microbes.
“[Germ-free mice] are a really good tool to try to determine the role of microbes in different types of diseases,” explained lead study author Dr Francine Marques, a National Heart Foundation Future Leader at the Monash University School of Biological Sciences.
They found that the germ-free mice given bacteria from those on a low-fibre diet developed high blood pressure, while the mice given bacteria from those on a high-fibre diet did not.
Fibre is not just protective. Not having fibre is detrimental.
Marques said that their hypothesis is that when our gut microbes digest and ferment, the fibre we eat releases compounds called metabolites.
“These metabolites have several roles in our body but one that is important is activating certain immune cells that are protective against the development of high blood pressure,” she said.
“Independent of eating fibre, even if they have zero fibre, we were able to show that if we add these metabolites to the drinking water of the animals it would prevent the development of high blood pressure.”
This immune response also led to a change in levels of hormones released when we are stressed, which are associated with high blood pressure.
While Marques acknowledges the limitations of animal studies, her team is currently conducting a human trial to validate the findings and they are, she said, “excited” about what their research is showing.
“We showed in a paper a few years ago that the well-known association between fibre intake and blood pressure was dependent on microbes in the gut,” she said. “But what our new study is showing is that fibre is not just protective. Not having fibre is detrimental. It’s actually causing a microbiome that is leading to the development of cardiovascular disease.”
Professor David Kaye, Director of Cardiology at Alfred Hospital and head of the Baker Institute Heart Failure, co-led the study.
“The study is significant,” he said, “because it identifies for the first time, how dietary fibre directly regulates heart and blood vessel health.”
It is recommended that Australian adults eat between 25 and 30 grams of dietary fibre each day, found in wholegrains, fruits, vegetables, nuts, legumes and seeds. Currently, less than 20 per cent of people meet these guidelines.
Marques said they are not yet sure whether the type of fibre we eat makes a difference, however, they have used resistant starch (found in green bananas, beans, peas and lentils, oats, barley and cooked and cooled pasta or rice) for their animal trials.
“The main message is we do need to make sure we’re having fibre in our diet and high levels,” Marques said. “Having more fibre won’t do any harm to anyone and will have a lot of different health benefits, not just for cardiovascular health.”
To be a part of their clinical trial, go to: https://www.marqueslab.com/gut
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