Australian scientists redefine dietary fiber classification for better health benefits

Australian food scientists have reclassified dietary fibers – beyond just soluble and insoluble – to better guide nutritional decisions and drive targeted health food products.

Dietary fibers 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 fibers.

For example, apples and bananas are both rich in dietary fiber but the fiber in each works very differently.

Our research is helping to understand which type of fibers we should eat to help address certain ailments."

Professor Raj Eri, Food Scientist, RMIT University

A new model for more tailored diets

In a new study published in Food Research International, the RMIT University team propose a more nuanced fiber classification based on five key features: backbone structure, water-holding-capacity, structural charge, fiber matrix and fermentation rate.

Study lead author and RMIT PhD candidate Christo Opperman said by starting with the key active features of fiber, this 'bottom-up approach' more accurately described each fiber's health impacts.

"For example, suppose you want to promote colonic health. In that case, you identify a fiber'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 fibers 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 fiber gap

Eri said there was already strong interest among dieticians, clinicians and food technologists – and of course consumers – on how to better integrate fiber into diets.

"In the countries surveyed, including Europe and the USA, every single population had a deficiency of fiber," Eri said.

"Considering fiber is one of the most important nutrients, this is extremely worrying."

While recommended dietary fiber 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 fibers has them grouped into soluble and insoluble fibers, which is based on whether they dissolve in water.

Insoluble fibers are seldom fermented in the large intestine and help keep us regular.

Soluble fibers are more readily fermented and can reduce cholesterol, glucose absorption and food craving.

But it's not always so straightforward. For example, often insoluble fibers can also rapidly ferment and reduce glucose absorption.

"Despite our evolving understanding of how central different types of fiber are to nurturing a healthy gut biome, our dietary fiber 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 fibers influence human physiology."

"Our framework is an essential step in addressing this gap," he said.

The researchers are now planning to investigate how a specific type of fiber (based on our new classification) modulates the microbiota and how we can utilize such knowledge for specific health applications.