Glycaemic Index of Eight Types of Commercial Rice in Malaysia

This experimental study was carried out to investigate the effect of eight types of commercial rice in Malaysia on blood glucose response and to determine their glycaemic index (GI) values. Ten healthy Malay volunteers (7 males, 3 females, BMI=23.6kgm-2, age=25.1years) participated in this study. The eight types of rice tested were three high fibre rice (HFR A, HFR B & HFR C), three white rice (WR D, WR E and WR F) and two fragrant rice (FR G and FR H). The subjects were required to go through the study protocol on eleven separate occasions (eight tests for the test rice samples and three repeated tests for the reference food) after an overnight fasting. Capillary blood samples were taken immediately before (0min) and 15, 30, 45, 60, 90 and 120min after consumption of the test foods. The blood glucose response was obtained by calculating the incremental area under the curve (iAUC). The GI was determined according to the standardised methodology. This study showed that out of eight types of rice tested, three (HFR B, WR E and WR F) could be categorised as having intermediate GI while the remaining five were considered high GI foods (HFR A, HFR C, WR D, FR G and FR H). The GI of HFR B (60 ± 5.8) and WR E (61 ± 5.8) were significantly lower than the reference food (glucose; GI=100) (p<0.05). No significant difference of GI value was seen between the reference food and the rest of the test rice (p>0.05). The GI value of the rice tested in descending order were HFR C, 87 ± 9.0 followed by HFR A (81 ± 6.7), FR G (80 ± 5.5), FR H (79 ± 7.6), WR D (72 ± 8.5), WR F (69 ± 8.3), WR E (61 ± 5.8) and HFR B (60 ± 5.8). There was no relationship between the dietary fibre content of the rice with the iAUC (r= -0.05, p=0.63) and GI values (r= -0.08, p=0.46). This shows that the GI values of the test rice were independent of the dietary fibre content of the rice. Other factors that may influence the GI value of rice include amylose content, gelatinisation process and botanical sources. The results of this study will provide useful information for dietitians and nutritionists in selecting the appropriate type of rice for the daily diet of diabetics. wide range of glycaemic index (GI) values from studies around the world (FosterPowell, Holt & Brand-Miller, 2002). The GI of white rice ranges from as low as 54 to as high as 121 (Brand-Miller, Pang & Bramall, 1992). This is likely due to the inherent botanical differences of rice from different countries (Foster-Powell, Holt & BrandMiller, 2002). Brand-Miller, Pang & Bramall (1992) emphasised the need for individual countries to carry out their own GI testing, particularly with raw agricultural products like rice, which are more likely to vary from one geographical location to another. This variation makes it difficult to classify rice as a high or low GI food, and advice to patients, notably diabetics, may be incorrect. The GI has been recommended to help guide food choices (FAO/WHO, 1998) because low GI foods have been shown to improve blood glucose control in diabetics (Brand-Miller et al., 2003b), reduce serum lipids (Opperman et al., 2004), increase insulin sensitivity (Frost et al., 1998) and improve B-cell functions (Wolever & Mehling, 2002). In addition, a low-GI diet has been associated with reduced risk of developing diabetes and cardiovascular diseases in some epidemiological studies (Salmeron et al., 1997a,b; Liu et al., 2000). Aside from the GI properties, a high fibre diet has been shown to be beneficial in controlling blood glucose and lipid profile (Jenkins et al., 2002). In breads, however, the significance of the quantity and quality of dietary fibre in the regulation of postprandial blood glucose is controversial (Juntunen et al., 2003). Despite their different dietary fibre contents, white and whole meal breads showed similar blood glucose responses both in healthy volunteers (Juntunen et al., 2002) and in diabetics (Jarvi et al., 1999). The objectives of this study are to determine the blood glucose response after consuming eight types of commercial rice in Malaysia and the GI value of each type of rice in healthy Malay respondents. This study also tests the hypothesis that high dietary fibre content of rice reduces the blood glucose response and demonstrates a low GI value. MATERIALS AND METHODS