Low carbohydrate does not mean low glycaemic index!

Nutrition Discussion ForumLow carbohydrate does not mean low glycaemic index!*Dumesnil et al. (2001) reported the results of a study from Laval University, Que ´bec, in which overweight men were fed under metabolic ward conditions for 6 d on each of three different test diets.They concluded that: '. . .a lowglycaemic index-low-fat -high-protein diet can produce a marked decrease in ad libitum energy intake without increasing hunger or decreasing satiety while having rapid and marked effects on metabolic risk variables'.However, the authors have provided no evidence that the effects they observed were in any way due to the use of low-glycaemic-index (GI) foods.The conclusions related to GI are unjustified because the paper fails to demonstrate that the GI of their low-GI -lowfat -high-protein diet is less than that of the control (American Heart Association; Krauss et al. 1996) diet.The GI of neither experimental diet is given.An appendix is provided giving sample menus from each dietary regimen and showing the GI values of the foods in each diet.However, the information is imprecise: there are no weights of foods given, in some cases the specific food is not indicated.Three foods, wholewheat bread, unsweetened jam and fresh fruits, provide most of the carbohydrate in the low-GI diet.The GI values of bread and jam are indicated as being: 'Undetermined, but probably , 51'.The GI of 'fresh fruits' is listed as being 36-53.We have tested commercial varieties of wholewheat bread available in Canada, and wholewheat bread baked in our laboratory, on several occasions.The lowest value ever obtained was 65 (Wolever et al. 1994a), although the value obtained was usually closer to 71 (Jenkins et al. 1983a(Jenkins et al. ,b, 1986(Jenkins et al. , 1988;;Wolever et al. 1986 Wolever et al. , 1994a)).Thus wholewheat bread is not a low-GI food.The published GI values of certain popular tropical fruits, readily available in Canada, are higher than the maximum value of 53 given by the authors; e.g.ripe banana (all yellow skin, GI 54), over-ripe banana (few brown spots on skin, GI 64) (Wolever et al. 1988), pineapple (GI 66) and watermelon (GI 72) (Foster-Powell & Brand Miller, 1995).Since the fruits used are not indicated, it is not possible to verify that the GI values cited are correct.To the best of my knowledge, there is no published GI value for jam, although Jenkins (DJA Jenkins and C Kendal, personal communication) found the GI of strawberry jam to be 84.The carbohydrates in regular jam consist of the sugars in the fruit, plus the sucrose or other carbohydrate added to sweeten and thicken the jam.Fruits contain varying proportions of sucrose, fructose and glucose with some, such as pear, peach and apricot, *All glycaemic index values quoted in this article are given on the glucose standard, i.e. the glycaemic index of glucose ¼ 100.