Investigating the relationship between lentil carbohydrate fractions and in vivo postprandial blood glucose response by use of the natural variation in starch fractions among 20 lentil varieties
Ramdath, D.D., Liu, Q., Donner, E., Hawke, A., Kalinga, D., Winberg, J., Wolever, T.M.S. (2017). Investigating the relationship between lentil carbohydrate fractions and in vivo postprandial blood glucose response by use of the natural variation in starch fractions among 20 lentil varieties. Food and Function, [online] 8(10), 3783-3791. http://dx.doi.org/10.1039/c7fo00972k
Plain language summary
Consumption of lentil results in blood sugar levels that are lower than other starchy foods, but the mechanism by which this effect is brought about is not fully understood. It is likely that the relative abundance of various starch fractions in lentil may be a contributing factor. In this study we use the fact that there is natural variation in starch fractions among different lentil varieties to investigate the relationship between starch components and blood sugar response after human volunteers consume different lentil varieties. We measured starch components using established laboratory methods; this allowed starch fractions to be characterized as rapidly digestible (RDS), slowly digestible (SDS) and resistant starch (RS) based on the amount of sugar released over a 120 minutes period. From this method the in vitro area under the starch hydrolysis curve (SHAUC) was calculated. For human testing 8 lentil varieties, representing a linear range of SDS, were consumed and blood sugar response was measured. The in vitro results showed that the rate of starch conversion to sugar was directly related to the amount of RDS and inversely related to the amount of RS in the 20 lentil varieties. In the human study we found that all 8 lentils had low glycemic index values (10 to 23). We also found that the in vitro SHAUC was predictive of the blood sugar response of human volunteers. These results confirm that lentils produce low blood sugar response in healthy human volunteers, but this is not reliably predicted by the individual starch fraction. However, in vitro SHAUC and a combination of RDS and RS may be predictive of the blood sugar response of lentils.
Consumption of pulses is associated with many health benefits by mechanisms that are not fully understood. This study sought to identify the starch component(s) in cooked lentils responsible for lowering postprandial glycemic response (PPGR). Rapidly digestible (RDS), slowly digestible (SDS) and resistant starch (RS) content of 20 varieties of cooked lentil were determined by in vitro methods and 8 varieties, representing a linear range of SDS, were chosen for a human trial with 10 participants to determine PPGR and glycemic index (GI). Among the 20 lentil varieties, RS accounted for 35% of the variation of in vitro area under the starch hydrolysis curve (SHAUC) (r = -0.587; p < 0.01), but RDS (r = 0.401; p = 0.080) and SDS (r = -0.022; p = 0.927) were not significantly related to SHAUC. Multiple linear regression of in vitro data resulted in an equation [SHAUCest = 30.9RDS - 63.6RS + 9680] that accounted for 70% of the variance in SHAUC, with SDS excluded due to collinearity. In the human trial all 8 lentils had low GI values (10 to 23). Neither GI nor area under the glucose response curve (AUC) was significantly related to RDS, SDS or RS (minimum p = 0.24). However, SHAUC and SHAUCest, respectively, were related to both GI (r = 0.704, p = 0.051; r = 0.773, p = 0.024) and AUC (r = 0.765, p = 0.027; r = 0.822, p = 0.012). These results confirm that lentils have low GI values, which is not reliably predicted by their RDS, SDS and RS contents when considered individually. However, in vitro SHAUC and a combination of RDS and RS may be predictive of the PPGR of lentils.