Low-glycemic carbohydrates such as pasta, oatmeal, whole-grains and vegetables take longer to digest and are thought to be more beneficial than high-glycemic carbs like white bread and cereals, which cause blood sugar levels to spike.
Until now Atkins products have been labeled with an approximate net carb value, calculated by subtracting carbohydrates that have little or no effect on blood sugar, such as fiber, glycerine and sugar alcohols, from the total carbs.
Atkins' low-glycemic approach was developed over a three-year period by clinical nutritionalist Dr Thomas Wolever and is said to be a much more accurate way of measuring the impact of carbs on the body.
Wolever conducted clinical trials on individuals to measure human blood-sugar response to certain food by measuring their baseline blood-sugar level, then comparing it with levels after eating. The net Atkins count for each food tested was developed from the average blood-sugar response across all participants who ate it.
Atkins claims its new, patent-pending methodology is a "unique scientific method that substantiates the low glycemic impact of Atkins products to confirm the accuracy of Atkins net carbohydrate labeling claims". But competitors see the new labeling as a shift in gear by the Ronkonkoma, New York-based company in response to waning popularity of the low-carb diet.
US rival NutriSystem says Atkins is following its example, after introduced a weight loss programme based on foods with a lower glycemic index two years ago. Since then, it claims sales have "skyrocketed", whereas Atkins has been criticized as a fad diet producing unsustainable results.
Matt Spolar, vice president of product technology at Atkins Nutritionals, explained reasoning behind the change: "We saw an opportunity to develop a better tool to help consumers have success doing Atkins."
He said that the overall impact on the diet is minimal, however. For most Atkins products the carb count information will remain unchanged. Those few that tested outside the acceptable range using the new system are being relabeled, reformulated or discontinued.
Amongst the products affected are Atkins Endulge Caramel Nut Chew, which is being reformulated after being found to have a net Atkins count of 6g, compared with 2g by the net carbs subtraction method, and Atkins Endulge Chocolate Candy Bar: Chocolate Almond, whch had a net Atkins count of 5g but 2g of net carbs. This product has now been discontinued.
Last week Atkins Nutritionals announced that it was ceasing its operations in the UK, which was the company's biggest European market.
"The reason Atkins failed in the UK is that its foods were engineered for the US market and people found the choice too limiting," said Dave Marshall, managing director of UK low carb food company Xcarb.
"The UK consumer missed the staples of mash, cereals and pasta as well as sweet alternatives such as chocolate and fruit. They also missed the convenience of ready meals and found the cost of living a low carb diet via Atkins rules prohibitive and expensive."
A survey last year that claimed more than 3 million Britons have tried the low-carbohydrate, high-protein diet, but most are thought to have had difficulty in sticking to the regime.