Efficacy of different fibres and flour mixes in South-Asian flatbreads for reducing post-prandial glucose responses in healthy adults

Purpose Type 2 diabetes (T2DM) is increasing, particularly in South-East Asia. Intake of high-glycaemic foods has been positively associated with T2DM, and feasible routes to reduce the glycaemic response to carbohydrate-rich staple foods are needed. The research question was whether different fibre and legume flour mixes in flatbreads lower postprandial glucose (PPG) responses. Methods Using a balanced incomplete block design, we tested the inclusion of guar gum (GG), konjac mannan (KM) and chickpea flour (CPF) in 10 combinations (2/4/6 g GG; 2/4 g KM; 15 g CPF, and 10 or 15 g CPF plus 2 or 4 g GG) in 100 g total of a control commercial high-fibre flatbread flour mix (“atta”) on PPG in 38 normal-weight adults. Self-reported appetite was an additional exploratory outcome. An in vitro digestion assay was adapted for flatbreads and assessed for prediction of in vivo PPG. Results Flatbreads with 6 g GG, 4 g KM, and 15 g CPF plus 2 or 4 g GG reduced PPG ≥30 % (p < 0.01), while no other combinations differed significantly from the control. A statistical model with four in vitro parameters (rate of digestion, %RDS, AUC, carbohydrate level) was highly predictive of PPG results (adjusted R 2 = 0.89). Test products were similar to the control for appetite-related measures. Conclusions The results confirm the efficacy of specific additions to flatbread flour mixes for reducing PPG and the value of the in vitro model as a predictive tool with these ingredients and product format. This trial is registered at ClinicalTrials.gov with identifier NCT02671214. Electronic supplementary material The online version of this article (doi:10.1007/s00394-016-1242-9) contains supplementary material, which is available to authorized users.


Supplemental
Fasting glucose (mmol/l) 5.35 0.14 In vitro starch digestion method In vitro starch digestibility was assessed by adaptations of the Englyst method [26,27], with which good correlations have been demonstrated between clinical postprandial glucose (PPG) responses and the in vitro starch digestibility measures of rapidly digestible, slowly digestible and resistant starch (RDS, SDS and RS) for a wide range of products [28]. The method was modified with the methods described by Sopade [29] and Van Kempen [30] to provide a glucose release profile and calculate the rate of digestion (k) using the Chapman-Richards model and the Area under the glucose curve over 120 min (AUC120) using the trapezoidal model.
A detailed description of the experimental conditions of all models is given in Supplemental Table 2. Our model ('URDV') was tested with the same types of food as used by Englyst et al [28], and Supplemental Figure 1 shows comparable results for RDS and SDS. Our model was also tested with reference materials used by Van Kempen et al [30] and Supplemental Table 2 lists the obtained parameters.
The additional inclusion of the simulated oral digestion stage by 30 seconds mixing with α-amylase will increase RDS and k. The chewing and wetting with saliva of the flatbreads is seen as an essential part of starch digestion. Furthermore the pH of the intestinal phase has been increased from 5.2 to 6.5, to reflect realistic human physiology. The amount of glucose, released during intestinal digestion, is expressed as fraction of the total carbohydrates in the chapatti. The carbohydrates content is estimated using the calculation:

Supplemental
In which: Wf = weight of flour mixture cf = carbohydrates content of flour mixture Wdb = weight of dough ball Wd = weight of dough Wc = weight of chapatti Since most of the digestion of chapatti takes place within the first 60 minutes, the initial rate of digestion would provide an additional parameter to discriminate between treatments. Therefore, non-linear regression was applied using the Chapman-Richards model as suggested by Van Kempen, as: In which: A = free glucose present in the sample before enzyme addition B = glucose released by exhaustive digestion K = rate of glucose release corrected for plateau effects C = sigmoidal/shape modifier corrected for plateau effects.
The fitted glucose curve for time (t) is 0 to 120 minutes is used to calculate the AUC120 using the trapezoidal model with the equation: The in vitro starch digestion parameters are listed in Supplemental Table 3.

In vitro prediction of in vivo data
The aim of the statistical analysis was to identify the best model to predict +iAUC over 120 minutes in the in vivo study from the in vitro data. The PPG response in the clinical trial are shown in the Table 3 of the main article text. All parameters that describe the in vitro digestibility (listed in Supplemental Table 4 above) plus 'slope to Cmax' were considered as input for correlation with the in vivo data. Initial correlations and scatter plots for each of these variables with +iAUC showed that a linear model was unlikely to provide good prediction, so a quadratic model was used.