Australian food scientists have reclassified dietary fibres - beyond just soluble and insoluble - to better guide nutritional decisions and drive targeted health food products.
Dietary fibres in fruit, vegetables, beans and whole grains are some of the most important food components for human health. They help digestion, weight management, blood sugar control, heart health, cancer prevention and more.
But RMIT University food scientist Professor Raj Eri said consumer advice on how best to use them for these various benefits is sorely lacking.
"Quite like how different medicines target different conditions, so too do different types of fibres," he said.
"For example, apples and bananas are both rich in dietary fibre but the fibre in each works very differently.
"Our research is helping to understand which type of fibres we should eat to help address certain ailments."
RMIT food scientist Professor Raj Eri with PhD candidate Christo Opperman.
A new model for more tailored diets
In a new study published in Food Research International, the RMIT University team propose a more nuanced fibre classification based on five key features: backbone structure, water-holding-capacity, structural charge, fibre matrix and fermentation rate.
Study lead author and RMIT PhD candidate Christo Opperman said by starting with the key active features of fibre, this 'bottom-up approach' more accurately described each fibre's health impacts.
"For example, suppose you want to promote colonic health. In that case, you identify a fibre's properties as defined by the bottom-up approach, which align with your desired outcome - in this case fermentation rate," Opperman said.
"Applying this framework can assure consumers, dieticians, clinicians and food technologists that they are receiving their desired health effect, which previously was a vague guessing game."
Opperman said the RMIT team have now taken 20 different types of fibres and studied how they interact specifically with microbiome in the gut.
"Until now, these types of specific interactions have been understudied, but with this framework as a beginning, we are on the verge of a much more helpful and detailed understanding," he said.
A global fibre gap
Eri said there was already strong interest among dieticians, clinicians and food technologists - and of course consumers - on how to better integrate fibre into diets.
"In the countries surveyed, including Europe and the USA, every single population had a deficiency of fibre," Eri said.
"Considering fibre is one of the most important nutrients, this is extremely worrying."
While recommended dietary fibre intake is 28-42 grams per day, Americans on average get only 12-14 grams per day and Europeans 18-24 grams per day.
Beyond soluble and insoluble
The current classification of dietary fibres has them grouped into soluble and insoluble fibres, which is based on whether they dissolve in water.
Insoluble fibres are seldom fermented in the large intestine and help keep us regular.
Soluble fibres are more readily fermented and can reduce cholesterol, glucose absorption and food craving.
But it's not always so straightforward. For example, often insoluble fibres can also rapidly ferment and reduce glucose absorption.
"Despite our evolving understanding of how central different types of fibre are to nurturing a healthy gut biome, our dietary fibre classifications remain simplistic between broad categories of soluble and insoluble types," Eri said.
"This binary classification of soluble and insoluble insufficiently captures the diverse structures and complex mechanisms through which dietary fibres influence human physiology."
"Our framework is an essential step in addressing this gap," he said.
Using their new classification, the researchers plan to explore how a specific type of fibre affects gut bacteria and how this information can be applied to improve health.
'Beyond soluble and insoluble: A comprehensive framework for classifying dietary fibre's health effects' is published in Food Research International (DOI: 10.1016/j.foodres.2025.115843)
