Proximate analysis.

* the compounds in green are determined quantitatively

** Note that carbohydrates calculated by difference also contain some non-carbohydrate components, like organic acids.

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Calculation of carbohydrates by difference combines uncertainties of the other macronutrient measures

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One way to determine carbohydrates is by difference. This approach is based on Weende’s proximate method of analysis where major compounds ( in g/100g) in a food are identified based on the chemical properties of the compounds (see scheme). Thus minor constituents (present in mg or m g per 100 g) are ignored. Originally this approach was developed for the analysis of animal feeds but is also applied to food analysis. The scheme below shows that for carbohydrate calculation, the other major constituents in the food are determined individually, summed and subtracted from the total weight of the food.

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Right. It is reasonable to assume that there are analytical uncertainties in the measurements of protein, ash, fat, and moisture. Because carbohydrates by difference values are based on the measurements of those macronutrients, all analytical uncertainties in the measurements of the other macronutrients are combined in carbohydrates by difference values.

Not right. It is reasonable to assume that there are analytical uncertainties in the measurements of protein, ash, fat, and moisture. Carbohydrate values by difference are based on protein, fat, ash and moisture values. Therefore, any uncertainty in one of these values will effect carbohydrate values calculated by difference.

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