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Frequently Asked Questions

Fibre

Dear Professor Wahlqvist,

I would like to gain some information on fibre. I understand that there are two main forms of fibre: soluble fibre (which slows the rate of digestion in the stomach), and insoluble fibre (which increases the speed of transit through the digestive tract). I also understand that both forms of fibre are carbohydrates which the body cannot fully digest.

Is it true to say that dietary fibre does not provide the body with energy? Hence, when counting carbohydrate grams from a particular food source, should an athlete like myself, who carefully controls the macronutrient intake of each meal, subtract the total fibre content from the total carbohydrate content, in order to arrive at the carbohydrate content of the particular food, which will be utilised as energy?

To illustrate an example of my question:-

If a tin of baked beans contains 15g of fibre and 56g of carbohydrate, would the usable (as energy) total amount of carbohydrate be 41g (i.e. 56-15)?

Sir, I would appreciate any information that you can provide me with.

Answer

For current policy on calculation of the energy (cal) value of carbohydrate in food, it is best to refer to the ANZFA website. With the most contemporary methods for food analysis, digestible carbohydrate is assessed seperately to dietary fibre since they each have methods for their own analysis.

Dietary fibre may or may not be fermentable in the large intestine - if it is, it has an energy (cal) value of about 3cal/gm as it is turned into short chain fatty acids by the gut bacteria and these are absorbed into the circulation where they contribute to the body fuel supply; if dietary fibre is not fermented in the large intestine, it has no energy (cal) value.

You can find more information about this is my book Food and Nutrition which you can purchase in the HEC bookstore, or in Food Facts (of which I am a co-author), which is free if you subscribe to the club.

Wishing you good health,
Prof. Mark Wahlqvist AO

Last Updated: October 29, 2001