Scientists Unveil Secret Language of Dietary Fiber

The humble banana and apple sitting in your fruit bowl might both be packed with fiber, but Australian scientists have discovered that their fiber types are speaking entirely different languages to your body.

This revelation comes from food scientists at RMIT University who have developed a more sophisticated classification system for dietary fiber that moves beyond the traditional soluble versus insoluble categories—a breakthrough that could transform how we approach nutrition for specific health concerns.

“Quite like how different medicines target different conditions, so too do different types of fibres,” said Professor Raj Eri, food scientist at RMIT University and one of the study’s authors. “For example, apples and bananas are both rich in dietary fibre but the fibre in each works very differently.”

The research, published January 31 in Food Research International, introduces a framework that classifies fiber based on five key features: backbone structure, water-holding-capacity, structural charge, fiber matrix and fermentation rate.

This reclassification matters because dietary fiber—found in fruits, vegetables, beans and whole grains—is critical for multiple aspects of health, including digestion, weight management, blood sugar control, heart health, and cancer prevention. Yet according to the researchers, personalized guidance on using different fiber types for specific health benefits has been surprisingly limited.

From Binary to Comprehensive

For decades, nutritionists have categorized dietary fiber into just two groups: soluble (dissolves in water) and insoluble (doesn’t dissolve in water). While this simplification made fiber easy to understand, it failed to capture the complex ways different fibers interact with our bodies.

“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 explained. “This binary classification of soluble and insoluble insufficiently captures the diverse structures and complex mechanisms through which dietary fibres influence human physiology.”

The traditional model suggests that insoluble fibers primarily help with regularity while soluble fibers reduce cholesterol and glucose absorption. But reality is more nuanced—certain insoluble fibers can rapidly ferment and reduce glucose absorption, contradicting their typical classification.

Breaking Down the New System

The team’s new “bottom-up approach” examines fiber at a more fundamental level. Lead author and RMIT PhD candidate Christo Opperman explained that their framework starts with key active features of fiber that align with specific health outcomes.

“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.

The new classification considers characteristics like whether fiber is linear or branched, its electrical charge, how it holds water, and how quickly gut bacteria ferment it—properties that directly influence how fiber functions in the body.

“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,” added Opperman.

The Global Fiber Gap

This reclassification comes at a critical time. Current dietary data shows a concerning “fiber gap” in many populations.

“In the countries surveyed, including Europe and the USA, every single population had a deficiency of fibre,” noted Eri. “Considering fibre is one of the most important nutrients, this is extremely worrying.”

While health authorities recommend consuming 28-42 grams of fiber daily, Americans average only 12-14 grams per day, with Europeans slightly better at 18-24 grams per day.

The researchers suggest their framework could help address this gap by making fiber recommendations more precise and effective, encouraging consumption of specific fibers for targeted health benefits.

From Research to Practical Applications

To demonstrate their model’s practical value, the team has begun mapping the specific interactions between different fiber types and gut microbiota.

“The RMIT team have now taken 20 different types of fibres and studied how they interact specifically with microbiome in the gut,” Opperman explained. “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.”

This research could eventually lead to more personalized nutrition recommendations and improved functional food products tailored to specific health needs.

For the everyday consumer, the implications could be significant. Instead of simply seeking high-fiber foods, we might eventually select foods with specific fiber profiles to address particular health concerns—whether that’s blood sugar management, cholesterol reduction, or digestive health.

The researchers are now planning further investigations into how specific fiber types modulate gut microbiota and how this knowledge can be applied to particular health conditions.

“Our framework is an essential step in addressing this gap,” Eri said, pointing to the future implications of this more nuanced approach to one of our most important but often overlooked nutrients.

As nutritional science continues to evolve, this research suggests that understanding the language of fiber might be key to unlocking its full potential for human health—fiber by fiber, benefit by benefit.