Food for Thought

Don’t sweat the small stuff when counting carbs

Pediatric dietitian Carmel Smart

Most people with type 1 diabetes on conventional insulin regimens (twice daily injections) need to eat similar amounts of carbohydrate-containing foods, at regular times over the day. For those on intensive insulin regimens, while it is still important to maintain a regular eating pattern, the days of matching foods to a rigid insulin regime are long gone.

One way or another, most people with type 1 diabetes still count carbs, especially those on multiple daily injections and pumps. They typically count their carbs in 1 gram increments, 10g portions or 15g exchanges to adjust their mealtime insulin dose to carbohydrate intake. The question then arises as to how precise their carb counts need to be, as many clinicians believe that counting in gram increments is necessary to achieve optimal glycemic control, particularly for people on insulin pump therapy.

According to pediatric dietitian Carmel Smart and researchers from the University of Newcastle and John Hunter Children’s Hospital, there’s no need to sweat the small stuff as there’s room for 10 grams error either way. In a study published in Diabetic Medicine, they found that with children using intensive insulin therapy, a single mealtime insulin dose calculated for 60g carbohydrate maintained postprandial blood glucose levels for meals containing between 50–70g carbs. The authors concluded a single mealtime insulin dose will cover a range of carbohydrate amounts without deterioration in postprandial control.

Which is just as well, as the latest study from this team in Diabetic Medicine reports that although children with type 1 diabetes and their caregivers (usually Mum) can estimate the carbohydrate content of meals with reasonable accuracy, large meals tended to be underestimated and snacks overestimated. ‘Very little is actually known about the ability of children to count carbs and whether one particular method (grams, portions or exchanges) for assessing carbs is better in this age group than others,’ writes Smart. ‘So we thought we would find out what they really know.’

The researchers asked 102 children and teenagers (aged 8–18 years) on intensive insulin therapy and 110 caregivers to independently estimate the carb content of 17 standardized meals using whichever method of method they had been taught (gram increments, 10g portions or 15g exchanges). ‘We found that teaching children and their caregivers carb counting in gram increments did not improve accuracy compared with carb portions or exchanges. The longer children had been carb counting the greater the mean percentage error. Core foods in non-standard quantities were most frequently inaccurately estimated, while individually labelled foods were most often accurately estimated,’ they write.

Of course, as GI News readers know, it’s not just the quantity of carbs that counts, it’s the quality. Smart’s study published in Diabetes Care reported that substituting healthy low GI foods for high GI choices helps reduce post-meal hyperglycemia and is good for the whole family. ‘In addition, young people with diabetes should try to always inject before they eat as this assists blood glucose control,’ says Smart.

Reality check on carb amounts in food. ‘Don’t get too carried away thinking that by counting every gram of carbohydrate you eat and every 0.05 of a unit of insulin you take your blood glucose levels will be perfect,’ writes Dr Alan Barclay in The Diabetes and Pre-diabetes Handbook. ‘It just doesn’t happen like this. It’s a fact of life that even the most processed of foods never contain exactly the same amount of carbohydrate in a serve as the label says.’

How does this happen? Well, what’s printed on the label is actually an average amount of carbohydrate per serving or per 100g for that food. There are small and completely natural variations in the amount of carbohydrate in food depending on where it is grown and the actual crop variety (different wheats and rices, for example, can have a different carb quantity and quality). Manufacturing and processing techniques produce small variations, too. This, along with the small differences you introduce each time you prepare yourself a ‘serve’ all adds up. So you can see how easily a 10–20% variation in the carbohydrate content of a food from what is printed on a food label can happen.

It’s not illegal either: food regulators such as Food Standards Australia and New Zealand recognise the natural variability of foods and allow for this with a 20-45% variation acceptable under the labelling regulations. This further highlights the impracticalities of ‘precisely’ counting carbs in 1 gram increments.

And for low carbers, there is international agreement that carbohydrate should not be restricted in children and adolescents with type 1 diabetes as it may have seriously harmful effects on their growth and development.

For more information contact: carmel.smart@hnehealth.nsw.gov.au