Scientists at RMIT University in Melbourne, Australia, have redefined the way dietary fibres are classified, moving beyond the traditional “soluble” and “insoluble” categories. Their new system, based on five key features, could transform how dietary fibre is used in food formulation and health guidance.

Dietary fibres from fruits, vegetables, beans and whole grains are essential for digestion, heart health, blood sugar control and even disease prevention. However, despite their benefits, many populations still consume too little fibre, and existing classifications fail to capture the complexity of how different fibres function in the body.

A more targeted approach to fibre

Professor Raj Eri, a food scientist at RMIT University, argues that current dietary recommendations are too broad and fail to guide consumers on the best fibre choices for specific health benefits.

Professor Eri explained:

Quite like how different medicines target different conditions, so too do different types of fibres. 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.”

To address this gap, the researchers propose a new fibre classification system based on five key properties: backbone structure, water-holding capacity, structural charge, fibre matrix, and fermentation rate. This approach, detailed in Food Research International, aims to provide a clearer link between fibre structure and its health benefits.

Precision nutrition for better health

Study lead author and RMIT PhD candidate Christo Opperman explained how this new classification could provide more accurate health advice. He said:

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.”

This method allows dieticians, food technologists, and consumers to choose fibres based on their specific health impacts rather than relying on outdated generalisations. The RMIT team has already studied 20 different fibres, mapping how they interact with gut microbiota.

Opperman added:

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.”

Addressing the global fibre deficit

Despite the well-known health benefits of fibre, most people don’t get enough of it.

Professor Eri highlighted that in all the countries surveyed, including Europe and the USA, every population showed a fibre deficiency. While the recommended daily fibre intake is between 28–42 grams, many populations fall short. On average, Americans consume just 12–14 grams per day, while Europeans get 18–24 grams per day.

He stressed that this is particularly concerning, given fibre’s crucial role as one of the most important nutrients.

Moving beyond soluble and insoluble

Traditional classifications divide fibre into soluble (which dissolves in water and supports heart health and blood sugar control) and insoluble (which aids digestion but is not usually fermented in the gut). However, the researchers of the study believe that this binary system is too simplistic.

Professor Eri concluded:

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. Our framework is an essential step in addressing this gap.”

The researchers now plan to investigate how specific fibres in their new classification system interact with gut microbiota and how they can use this knowledge for targeted health applications.