There’s a lot more to it than soluble and insoluble indigestible bits.
All the Back Page’s formal learning about nutrition happened in about year 8. They taught us about the five food groups and that some foods had fibre in them and that fibre was A Good Thing.
This knowledge served me well until some point later when I learned the mind-blowing distinction between soluble and insoluble fibre.
Imagine how it has shattered yet again my deep and broad understanding to read this paper from RMIT researchers, which says our fibre classification is basic and we need a new approach.
A bottom-up approach, in fact.
Yes, their words: “a ‘bottom-up’ approach that utilises fundamental aspects to determine overall effects”.
Published in Food Research International, the paper proposes a framework that more accurately captures the structural and functional diversity of fibre types, allowing more accurate prediction of their health benefits.
This could help us close the “fibre gap” between the recommended intake and what we actually eat, the authors write.
The wide variety of dietary fibre types includes non-starch polysaccharides, resistant starches, non-digestible oligosaccharides and synthetic carbohydrates; each is a complex of monosaccharides (glucose, galactose et al.).
It’s probably unsurprising, then, that the water-solubility binary fails to capture all the diversity of health effects – especially since many of these effects don’t correspond with the binary and when all fibre-containing foods have some of both.
Even the term microbiota-accessible carbohydrate, to describe those fibres scarfed by our gut inhabitants, isn’t a completely useful add-on as it varies both by individual human and by population.
The five main structural features the authors want us to think about are backbone structure, water-holding capacity, structural charge, fibre matrix and fermentation rate – much more of a mouthful – each of them with several subcategories.
Pure cellulose, for example, is an insoluble fibre under the ancien regime.
Using the “bottom up” approach (don’t tell me it’s not funny), cellulose has a slow fermentation rate, a linear backbone structure with long chains, neutral charge, rigid fibre matrix and medium water-holding capacity.
These features, apparently, mean it requires specific bacteria for its degradation, is useful in aiding stool bulk, has low binding ability for trapping intestinal molecules, may not adhere to cations and is suitable for aiding stool softening and inducing satiety.
“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,” said lead author and RMIT PhD candidate Christo Opperman, whose team has taken 20 different types of fibres and studied how they interact with gut microbiota.
It’ll take a bit more education, it’s fair to say, before consumers can attribute those purposes to those molecular features – so they’ll be relying on you.
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