08 May 2025 Beyond insoluble and soluble: A new framework for fibre

Australian researchers are paving the way for more targeted health food products with a proposed reclassification of the traditional soluble vs insoluble dietary fibre model...

Raj Eri, a professor of food science at the Royal Melbourne Institute of Technology (RMIT), believes that the oversimplification of dietary fibre into just soluble or insoluble categories is a major misconception.

To address this, Eri and PhD candidate Christo Opperman have developed a more detailed and accurate fibre classification system beyond these two traditional labels, asserting that this could provide deeper insights into the specific health benefits associated with different fibre types.

Ultimately, they envision the future development of a standardised rating system for dietary fibre, akin to Australia’s Health Star Rating or the Nutri-Score used voluntarily across several European nations.

Such labelling could not only display fibre quantities but also clearly communicate their known health outcomes, such as alleviating constipation, reducing inflammation, or aiding weight management.

However, Eri points out that establishing such claims would require robust scientific evidence, especially fibres’ influence on the gut microbiome.

Five key properties for reclassification

In their study published in Food Research International, Eri and Opperman propose a fibre classification based on five fundamental properties:

• Backbone structure describes the molecular composition of the fibre which impacts its behaviour in the digestive system. Fibres may have linear or branched structures, affecting fermentation, solubility and nutrient interactions.
  
  For example, cellulose, found in plant cell walls, has a linear, digestion-resistant structure, while beta-glucan has a branched, flexible form that can form viscous solutions — important for lowering cholesterol. Sources of beta-glucan include oats, yeast, and mushrooms.
• Water-holding capacity indicates how much water a fibre can absorb and retain, influencing stool bulk and constipation prevention.
• Structural charge refers to the electrical charge of the fibre which can be negative, neutral or positive. Negatively-charged fibres contain functional groups such as carboxyl, phenolic, or sulphate groups, enhancing their ability to bind toxic metals like arsenic and lead and increasing water retention.
• The fibre matrix describes the physical state of the fibre once ingested and how it behaves in the stomach.
• Fermentation rate measures how quickly gut bacteria break down the fibre, producing short-chain fatty acids that support gut and metabolic health.

Enhancing fibre-rich food appeal

Daily fibre intake recommendations vary globally, but generally, adults are encouraged to consume about 25 to 30 grams daily. Unfortunately, most people fall short; for example, the average intake in the UK is around 20 grams.

Eri believes that greater consumer education and understanding of this reclassification framework could improve fibre consumption. He notes that many current fibre products do not emphasise the distinct effects of different fibre types based on their properties.

Increasing awareness about how specific fibres impact the gut microbiome and overall health could empower consumers to make more personalised dietary choices.

Since different fibres interact uniquely with the gut microbiome, Eri sees personalised nutrition as a promising future direction for fibre recommendations. By accurately assessing individual microbiome responses to diet, tailored nutritional strategies could be developed to optimise health benefits.

“In the coming five to ten years, genomic and microbiome analyses are likely to become standard tools, enabling fully customised therapeutic approaches,” he states. This might include modulating microbial diversity through targeted fibres and specific nutritional interventions.”

Aligning functionality with consumer preferences

Combining functionality with consumer taste preferences could significantly boost acceptance and overall fibre intakes, Eri explained.

“Mild processing to enhance taste and texture, in my view, poses no issue – especially if it helps align with consumer expectations,” he said. “Our classification system can be readily applied to processed fibre products.

“In fact, understanding which fibre properties drive specific health benefits offers the food industry a valuable framework for incorporating these attributes while also optimising the overall eating experience.”

Source: ScienceDirect.com, Ingredientsnetwork.com