Rice: a high or low glycemic index food?1'2 - American Journal of ...

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GLYCEMIC INDEX OF RICE 1035 TABLE 1 The composition and weight ofthe foods Foods Protein (nitrogen X 6.25) Fat Carbohydrate by difference Weight of uncooked 50-g carbohydrate portion Preparation % % % g Calrose white 5.7 0.5 79.9 62.6 Boiled for 14 mm Calrose brown 6.6 2.7 75.6 66.1 Boiled for 35 mm Pelde white 6.4 0.5 79.6 62.8 Boiled for 14 mm Pelde brown 7.2 2.9 75.4 66.3 Boiled for 30 mm Pelde (parboiled)5 7.0 1.0 79.4 63.0 Boiled for 14 mm Doongara white (high amylose) 8.0 0.6 77.5 64.5 Boiled for 14 mm Doongara brown (high amylose) 8.7 2.5 74. 1 67.5 Boiled for 30 mm Sunbrown Quick 8.3 3.0 77.4 64.6 Boiled for 16 mm Waxy rice (0-2% amylose) 7.3 0.8 77.2 64.8 Boiled for 14 mm Rice cakes 8.0 2.7 8 1.5 6 1.3 Puffed product Rice bran 13.7 22.4 47.4 52.8t Pur#{233}ed with boiling water and flavoring Brown rice pasta 8.9 2.6 75.5 66.2 Boiled for 16 mm Wheat pasta 12. 1 0.2 75.9 65.9 Boiled for 20 mm Rolled oats 8.9 9.7 68.8 72.7 Boiled for 10 mm Rolled barley 7.5 2.4 76.9 65.0 Boiled for 10 mm S Sungold: Rice Growers Cooperative Ltd. Leeton, NSW. t Weight of 25-g carbohydrate portion. by using the glucose hexokinase method on a Cobas-Fara centifugal analyzer (Roche Diagnostica, Basle, Switzerland) and insulin by radioimmunoassay with the Bio-RIA ‘25I-Insulin Chromacode Radioimmunoassay kit (Bio-Mega Diagnostica Inc. Hamon, Montreal). The GI and insulin index (II) of each food was calculated as described previously (3) by using a 50-g carbohydrate portion of white bread as the reference food. For rice bran a 25-g carbohydrate portion was consumed and the incremental area under the curve was doubled. The GI was then multiplied by the factor 70/ 100 to express the final result on a scale where glucose = 100. When glucose is used as the reference food the GI of bread is 70 (2). The mean ± SE ofeight subjects was calculated. In some instances, one or two subjects gave a GI or II outside two SDs from the mean of the group. Their results were excluded and the mean of the remaining subjects reported. Comparisons between the foods were made by using two-way analysis of variance and the Bonferroni adjustment of the Student’s t test. Linearregression analysis was used to test for an association between glycemic and insulin responses. The protocol was approved by the Medical Ethical Review Committee of the University of Sydney and all subjects gave written, informed consent. Results The GI and II of the foods tested are shown in Table 2. The GIs of the white rices ranged from 64 ± 9 to 93 ± 1 1 . The rice with a higher amylose content (Doongara, 28% amylose) gave a significantly lower GI and II (P < 0.01) than did the normalamylose rice varieties (Calrose and Pelde, 20% amylose). The waxy rice with 0-2% amylose had a GI similar to that of those containing normal amounts of amylose. The GIs of the brown rices were similar to their white counterparts except for the Pelde variety. Pelde brown rice (GI = 76 ± 1 1) gave a significantly lower GI than did white Pelde (GI = 93 ± 1 1, P < 0.0 1). The parboiled (converted) Pelde rice gave a high GI (87 ± 7). Brown rice pasta and rice cakes gave high GIs (92 ± 8 and 82 ± 1 1, respectively) whereas rice bran gave an extremely low GI ( 19 ± 3). The wheat pasta (GI = 58), rolled oats (GI = 58), and rolled barley (GI = 66) gave results that were similar to those reported by others (3). TABLE 2 The glycemic and insulin indexes ofthe foods5 Foods Glycemic index (glucose = 100) Insulin index (glucose = 100) Calrose white (n = 8) 83 ± 13 67 ± 15 Calrose brown (n = 8) 87 ± 8 51 ± 7 Pelde white (n = 7) 93 ± 1 1 67 ± 1 1 Pelde brown (n = 8) 76 ± 6 55 ± 10 Pelde (parboiled) (n = 8) 87 ± 7 57 ± 6 Doongara white (high amylose) (n = 8) 64 ± 9 40 ± 10 Doongara brown (high amylose) (n = 8) 66 ± 7 39 ± 6 Sunbrown Quick (n = 8) 80 ± 7 54 ± 6 Waxy rice (0-2% amylose) (11 = 7) 88 ± 11 89 ± 19 Rice cakes (n = 6) 82 ± 1 1 73 ± 12 Rice bran (n = 8) 19 ± 3 23 ± 4 Brownricepasta(n=6) 92±8 72±18 Wheat pasta (n = 6) 58 ± 7 52 ± 9 Rolled oats (n = 7) 58 ± 4 54 ± 12 Rolled barley (n = 8) 66 ± 5 64 ± 1 1 S SE. The rice with a higher amylose content (Doongara, 28% amylose) gave a significantly lower glycemic index and insulin index (P < 0.0 1) than did the normal-amylose rice varieties (Calrose and Pelde, 20% amylose). Downloaded from ajcn.nutrition.org by guest on August 9, 2014
1036 MILLER ET AL The II ofthe rices correlated positively with their GI (r = 0.75, P < 0.05) but were relatively low compared with the GI. That is. the regression equation predicts that a rice with a GI of 80 has an II of 60. Discussion These results indicate that most varieties of rice sold in Australia, whether white, brown, or parboiled, should be classified as high-GI foods. Only one variety with a higher amylose content (Doongara) could be said to be potentially useful in low- G1 diets. The white Doongara rice had a GI and II of 64 and 40, respectively. These values are similar to those ofwheat pasta and porridge, which are recognized as low-GI foods. Rice bran, which is rich in fiber and oil, had an extremely low GI and may be a useful supplement in diabetic diets. The relationship between amylose content and GI ofrice may be exponential rather than linear. The GI of a rice with 20% amylose is already very high: 93 ± 1 1 in the Pelde variety. It is conceivable that this is approaching the maximum that is physiologically possible (the glycemic response to a similar carbohydrate load of glucose is not much higher). Hence, reducing the amylose content to only 0-2% amylose appears to make little difference. However. increasing amylose has a pronounced effect that has been shown by others (7). There are now varieties of rice with 35% amylose that may be predicted to have lower GIs than that ofthe Doongara rice (28% amylose) studied here. The parboiled rice in the present study gave a high GI (87 ± 7), unlike the parboiled rice studied by Jenkins et al (1) (GI = 54, glucose = 100). Parboiling ofrice involves steeping paddy rice in water at 60 #{176}C for > 1 h followed by steaming, drying, and milling. This process does not appear to alter the glycemic response because the GI of this variety of rice (Pelde) was 93 ± 1 1 before and 87 ± 7 after parboiling (P> 0.05). The parboiled rice used by Jenkins et al may have a low GI because the variety used has a high amylose content rather than because ofthe parboiling process per se. This suggestion, however, needs to be corroborated by GI testing and amylose:amylopectin analysis of other parboiled rices. An unexpected observation was the relationship between GI and II: the II was usually lower on the relative scale than was the GI of the foods. For example, the GI of Calrose brown rice is 83 but its II was only 5 1 . We have no explanation for this result unless bread, the reference food, is unique in its capacity to stimulate insulin. The effect may be increasingly observed as glycemic and insulin responses to real foods are measured. Collier et al (8) reported that insulin responses to carbohydrate foods were potentiated by coingestion oflarge amounts offat, ie, insulin responses were higher than the relative glycemic response if fat was added to the food. In the present study, fat content is negligible and insulin secretion is decreased relative to the glycemic response. The higher protein content of wheat pasta and rice bran may explain the higher parity of GI and II for these two foods. Coingestion of protein is known to increase the insulin response to a carbohydrate load (9). Findings such as this indicate that both GI and II should be considered when determining the optimal carbohydrate foods for individuals with diabetes. Insulin concentrations are a major determinant of blood cholesterol and triglyceride concentrations and influence the progression ofcoronary heart disease (10). We cannot assume that a food with a high glycemic response will have a high insulin response. It may be possible that many rice varieties, despite having a high GI, can be included in diets that improve carbohydrate and insulin metabolism in individuals with diabetes. Both the Canadian and the French groups have specifically included rice in their long-term GI diet studies (4, 5). In the Canadian studies, parboiled rice with a GI of54 (glucose = 100) was specified and in the French studies a rice with a GI of 56 (measured directly) was used. All subjects received a 50-g carbohydrate portion of white bread as the reference food in this study. However, we then adjusted all the results down by a factor of 70/100 so that glucose would theoretically have the highest score on the scale, ie, 100 [bread has a GI of 70 if glucose is the standard (2)]. We feel strongly that an index where glucose is 100 is easier to understand because, theoretically, nothing is likely to be higher than this. Jenkins et al (1) have made this adjustment in the other direction to many oftheir foods in order to express their early results with a white-bread standard ( 1 ). Their decision to make white bread - 100 has resulted in some confusion. We recommend that GI testing and calculation be carried out as we have done, with the final result expressed on a scale where glucose is 100. This means that any food can be used as the standard as long as its relationship to a 50-g glucose load is known. These results emphasize the need for individual countries to carry out their own GI testing, particularly of raw agricultural products, which are more likely to vary from one geographical location to another than do processed products, such as breakfast cereals. The findings also raise questions about the value of the GI alone without knowledge ofthe insulin response. In Australia, long-term studies are needed of the clinical utility of low-GI diets that specifically incorporate rice. C] References 1. lenkins DIA. Wolever DIA, Jenkins AL. Starchy foods and glycemic index. Diabetes Care 1988:11:149-59. 2. Jenkins DJA, Wolever TMS, Taylor RH. et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am I Clin Nutr 1981:34:362-6. 3. Brand IC. Nicholson PL, Thorburn AW, Truswell AS. Food processing and the glycemic index. Am I Clin Nutr 1985:42:1192-6. 4. Fontvieille AM, Acosta M, Rizkalla SW, et al. A moderate shift from high to low glycemic index foods for 3 weeks improves the metabolic control of Type I (IDDM) diabetic subjects. Diabetes Nutr Metab 1988:1:139-43. 5. Collier GR. Giudici 5, Wolever TMS, et al. Low glycemic index starchy foods improve glucose control and lower serum cholesterol in diabetic children. Diabetes Nutr Metab 1988:1:11-18. 6. Brand IC. Colagiuri S. Crossman 5, Allen A, Roberts DCK, Truswell AS. Low glycemic index foods improve long term glycemic control in NIDDM. Diabetes Care 1991:14:95-101. 7. luliano BO. Goddard MS. Cause of varietal difference in insulin and glucose responses to ingested rice. Plant Foods Hum Nutr 1986:36:35-41. 8. Collier G, McLean A, O’Dea K. Effect ofco-ingestion offat on the metabolic responses to slowly and rapidly absorbed carbohydrates. Diabetologia 1984:26:50-4. 9. Nuttall FQ. Mooradian AD. Gannon MC, Billington C, Krezowski P. Effect ofprotein ingestion on the glucose and insulin response to a standardized oral glucose load. Diabetes Care 1984:5:465-70. 10. Zavaroni I, Bonora E, Pagliara M, et aI. Risk factors for coronary artery disease in healthy persons with hyperinsulinaemia and normal glucose tolerance. N Engl I Med 1989:320:702-6. Downloaded from ajcn.nutrition.org by guest on August 9, 2014
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