Pulses are important components of healthy diets, known for their low glycaemic index. However, the outcomes of the trials regarding the impact of pulse consumption on markers of glycaemic control are considerable variable. A systematic review and meta-analysis was conducted to comprehensively review the evidence from intervention studies on the effect of pulse consumption on acute glucose response and long-term glycaemic indices. The meta-analysis revealed significant reduction of -2.90 mmol/L and -1.38 mmol/L in postprandial glucose in adults with and without type 2 diabetes respectively. Long-term pulse consumption significantly attenuated fasting blood glucose in normoglycaemic populations by -0.06 mmol/L; and fasting blood glucose, glycated haemoglobin, and homeostatic model assessment of insulin resistance in type 2 diabetes adults by -0.54 mmol/L, -0.17%, and -0.47 respectively. However, the effect size (ES) varied considerably across the trials with high degree of heterogeneity with no significant effect of pulse type, dose and duration of the trial. In addition, variations in the physical form of the pulses significantly impacted postprandial glycaemic response, although this aspect has so far received little attention. Therefore, an acute postprandial study was designed in order to demonstrate the impact of food processing on postprandial glycaemic and satiety responses. The cross-over trial investigated the effect of three different physical forms of chickpeas i.e. whole chickpeas (ChW), pureed chickpeas (ChPu), and chickpea pasta (ChF) against instant mashed potatoes (Con) as a carbohydrate-matched control group. Baseline and postprandial interstitial glucose responses, captured by continuous glucose monitoring, revealed lower postprandial glycaemic incremental area under the curve (iAUC) for 3 hours after chickpea intake in comparison with the control by 57.7%, 68.8% and 59.4% for ChW, ChPu, and ChF respectively. Postprandial subjective satiety and appetite responses were determined using visual analogue scale (VAS), covering hunger, fullness, and prospective food intake, which indicated significant hunger reduction and fullness increase after intake of all three forms of chickpeas compared to the control.
Further, an in vitro digestion experiment was conducted using the static INFOGEST protocol, involving the food samples that were used in the human study, to compare and correlate carbohydrate digestibility in these samples with the outcomes of the in vivo glycaemic response study. In vitro digestion results revealed limited bioaccessiblity of chickpea carbohydrates compared to potato control irrespective of chickpeas being processed differently. The in vitro digestibility outcomes significantly correlated with the mean postprandial glycaemic responses in vivo.
In conclusion, the systematic analysis of pulse based intervention studies and the in vivo trial revealed that pulse consumption improve the markers of glycaemic control regardless of their physical forms. Pearson correlations indicated strong associations between the outcomes of the degree of carbohydrate digestibility of various pulses in vitro and their postprandial glycaemic index in vivo and hence simulated in vitro digestion techniques could be utilised to prior conducting glycaemic human studies to predict physiological response. Different processing methods have minimal effect on carbohydrate digestibility from pulses and hence do not eliminate their low glycaemic index benefits. Therefore, pulse consumption should be included in dietary guidelines as a distinctive group for regular consumption.
