GI Symbol News with Alan Barclay

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Can you count on the carbs?

Alan Barclay

A reader recently asked about the accuracy of the carb count (in grams) on food labels. It’s an excellent question and there isn’t a simple answer. Under most national ‘food laws,’ two ‘carb counting’ methods are allowed.

  • The amount of carbohydrate listed on the food label can be determined by ‘difference’ – the amount of protein, fat and fibre is measured, and whatever is left over is called available carbohydrate.
  • Alternatively, carbs are measured by ‘direct analysis’, where each of the different sugars and starches in a food are measured and the totals are given.

Not surprisingly, carb counts based on difference will be intrinsically less reliable than those from direct analysis. But direct analysis is time consuming and rather costly, so the carb counts you see on food labels in the supermarket are typically calculated by the difference method.


Although measuring seems to be the way to go for accuracy, there’s a fair bit of natural variation in most foods we eat: they are grown in the ground, not produced under strict controls in a laboratory, so the carb count in a food can typically vary from variety to variety, crop to crop, batch to batch …

So, back to the food labels. While it is difficult to give a reliable estimate for carb quantities in packaged foods, variations of up to 20% are not unusual. That means for most of us, there’s little justification for counting carbs to the nearest gram – the values on most food and drink labels simply aren’t that accurate. However, some people (like those with diabetes) clearly need a practical system for estimating the amount of carbohydrate in foods so they can match their insulin or oral hypoglycaemic agents to what they eat. What’s the most practical tool they can use to help them do this reasonably accurately without fuss and a calculator?

Research has proven that carbohydrate exchanges (an average of 15 grams of carbohydrate per typical household serve of food, with an allowance for variation of 12–18 grams per serve) or portions (10 grams of carbs per serve) provide equally satisfactory estimates of the amount of carbohydrate in food to enable most people with diabetes manage blood glucose levels satisfactorily.

Of course, the amount of carbohydrate in a food is only one part of the equation when it comes to good health – the GI is equally important for all of us. Email us for more information:

Dr Alan W Barclay, PhD
CEO, Glycemic Index Ltd
Phone: +61 2 9785 1037
Mob: +61 (0)416 111 046
Fax: +61 2 9785 1037