Prof Jennie Brand-Miller answers your questions.
I’m confused about carb counts. What’s the difference between total carbs, net carbs and available carbs and does it really matter?
This very sensible question is complicated for several reasons. Let’s start with the labelling regulations of the country you live in. In the United States, for example, the total carbohydrate (in grams) listed on the nutrition facts panel includes fibre, so do the carb counts in diabetes exchange lists. In just about every other part of the world, the total carbohydrate listed in the nutrition information panel excludes fibre (and the same goes for diabetes exchange lists). Why? Unlike starches and sugars, fibre is not broken down during digestion. And that’s where terms like “available” or “net” carbs come in. In the US, net carbs = total carbs minus fibre = available carbs. Many low-carb weight–loss plans, including the New Atkins Diet, also use “net carbs” in their diet plans.
Then there’s how carbs are counted in a food and how accurate that process is. Under most national “food laws,” two “carb counting” methods are allowed.
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. However, 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 different seasons, climatic conditions and subject to different doses of fertiliser, they are 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.
- The amount of carbohydrate listed on the food label can be determined by “difference” – the amount of protein, fat, fibre, ash and water 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.
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 hypoglycemic 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 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.
Total Wellbeing Diet plus low GI carbs online program.
Participants are being sought to take part in a 12-week trial of the new online Total Wellbeing Diet. Professor Manny Noakes, Research Director for CSIRO’s Nutrition and Health Flagship and co-author of the CSIRO Total Wellbeing Diet, said “The trial will help us to assess how we can inspire healthy eating and provide more support to those that need to lose weight – which is a major goal of the Total Wellbeing Diet project,” Professor Noakes said.
- Participants who weigh in each week during the 12-week program will pay nothing; with the introductory price of A$99 being fully refunded.
- To find out more about the trial or register, visit: www.totalwellbeingdiet.com