Abstract:
Background: Low Glycaemic Index (GI) diet has shown benefits on type 2-diabetes management. In New Zealand, different varieties of kumara are a staple CHO source, yet GI values are controversial. Aim: To determine the GI of 2 varieties of kumara by testing 2-hr blood glucose response when hot, cooled and with skin compared with hot standard potato, using 50g glucose reference standard. Methods: Adhering to international methods, 10 healthy adults completed a 6-arm randomised, crossover comprising red kumara/hot(rk/hot), red kumara/hot with skin(rk+s/hot), golden kumara/hot(gk/hot), red kumara/cooled(rk/cool), standard potato/hot(p/hot), and glucose control(gc). Fixed weight of test foods were given, containing 50g of available CHO (calculated). Capillary fingerprick glucose was measured at fasting baseline, 15, 30, 45, 60, 90 and 120min. GI was calculated as % of incremental area under the gc curve (iAUCglucose). Statistical analysis included one-way-ANOVA and Tukey’s posthoc for pair-wise multiple comparisons (PRISM, v7.0). Results: Participants (2 men, 8 women, 60% Caucasian, 40% Asian) mean (SD) age was 26.9(6.3)years, BMI 22.9(2.1)kg/m2, fasting blood glucose 4.7(0.35)mmol/L. All kumara test foods assessed were classified as high GI(>70). Data between individuals was highly variable and 20(40%) of 50 test foods generated a glucose curve greater than corresponding gc. GI of the 5 test foods[mean(SEM)] were significantly different: rk/hot, 99(20); rk+s/hot 87(11.5); rk/cool 79(12.4); gk/hot 87(13.1); p/hot 68(14.2);(main effect, ANOVA, P=0.0230). GI of kumara varied by variety and also cooking method, although differences were small. All tended to be greater than p/hot, significant only for rk/hot(Tukeys, P<0.05). There was no difference between rk +/- skin(P>0.05), or rk/hot and gk/hot(P>0.05). Conclusion: All kumara had higher GI than potato with no variety providing low GI option; cooled had lower GI than hot. GI was based on calculated 50g bolus of available CHO, with possible false high values; available CHO (measured) may be required for validation.