You can estimate calories from fibre by assuming that fibres fermented by bacteria in the gut provide approximately 2 calories per gram of fibre consumed. This is the commonly accepted conversion factor used by the FDA.
Here's a breakdown of how this works:
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Fibre and Fermentation: Dietary fibre is a type of carbohydrate that the human body cannot fully digest. However, bacteria in the colon can ferment some of these fibres.
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Production of Short-Chain Fatty Acids (SCFAs): This fermentation process produces short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate. These SCFAs are absorbed into the bloodstream and can be used as a source of energy.
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Calorie Estimate: While the precise caloric value of different types of fibre varies depending on their fermentability, the FDA uses an average value of 2 calories per gram for labelling purposes.
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Calculation: To estimate the calories from fibre in a serving of food, simply multiply the grams of fibre by 2.
- Example: If a food product contains 5 grams of fibre, you would estimate that it contributes approximately 10 calories (5 grams x 2 calories/gram) from fibre.
Important Considerations:
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Not all fibre is fermented equally: Some fibres are more readily fermented than others, meaning their actual caloric contribution could be higher or lower than the 2 calories/gram estimate.
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Individual Variation: The gut microbiome composition varies from person to person, which can affect the efficiency of fibre fermentation and the subsequent caloric yield.
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Labelling Purposes: This 2 calories/gram value is primarily used for food labelling and provides a reasonable approximation. It's not a precise measure of the energy derived from fibre in every individual.
Therefore, while it is an estimation, multiplying the number of grams of fibre by 2 provides a standard and practical way to approximate the caloric contribution of fibre in food.
