Determining the glycaemic responses of foods: conventional and emerging approaches.

A low-glycaemic diet is crucial for those with diabetes and cardiovascular diseases. Information on the glycaemic index (GI) of different ingredients can help in designing novel food products for such target groups. This is because of the intricate dependency of material source, composition, food structure and processing conditions, among other factors, on the glycaemic responses. Different approaches have been used to predict the GI of foods, and certain discrepancies exist because of factors such as inter-individual variation among human subjects. Besides other aspects, it is important to understand the mechanism of food digestion because an approach to predict GI must essentially mimic the complex processes in the human gastrointestinal tract. The focus of this work is to review the advances in various approaches for predicting the glycaemic responses to foods. This has been carried out by detailing conventional approaches, their merits and limitations, and the need to focus on emerging approaches. Given that no single approach can be generalised to all applications, the review emphasises the scope of deriving insights for improvements in methodologies. Reviewing the conventional and emerging approaches for the determination of GI in foods, this detailed work is intended to serve as a state-of-the-art resource for nutritionists who work on developing low-GI foods.

Increased oral processing and a slower eating rate increase glycaemic, insulin and satiety responses to a mixed meal tolerance test.

PURPOSE: Variations in specific oral processing behaviours may contribute to differences in glucose, insulin and satiety responses to a standardised test meal. This study tested how natural variations in oral processing between slower and faster eaters contribute to differences in post-prandial glucose (PP glucose), insulin response (PP insulin) and post-meal satiety for a standardised test meal. METHODS: Thirty-three participants with higher risk for type 2 diabetes consumed a standardised test-meal while being video recorded to derive specific oral processing behaviours. Plasma glucose, insulin and satiety measures were collected at baseline, during and post meal. Participants were split into slower and faster eaters using median split based on their eating rates and individual bolus properties were analysed at the point of swallow. RESULTS: There were large variations in eating rate (p < 0.001). While there was no significant difference in PP glucose response (p > 0.05), slower eaters showed significantly higher PP insulin between 45 and 60 min (p < 0.001). Slower eaters had longer oro-sensory exposure and increased bolus saliva uptake which was associated with higher PP glucose iAUC. Faster eating rate and larger bolus particle size at swallow correlated with lower PP glucose iAUC. A slower eating rate with greater chews per bite significantly increased insulin iAUC. Faster eaters also consistently rated their hunger and desire to eat higher than slower eaters (p < 0.05). CONCLUSIONS: Natural variations in eating rate and the associated oral processing contributed to differences in PP glucose, PP insulin and satiety responses. Encouraging increased chewing and longer oral-exposure time during consumption, may promote early glucose absorption and greater insulin and satiety responses, and help support euglycaemia. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT04522063.

A comparison between whole grain and pearled oats: acute postprandial glycaemic responses and in vitro carbohydrate digestion in healthy subjects.

PURPOSE: To compare the glycaemic response of whole grain oat kernels and pearled oats cooked under normal pressure or higher pressure and examine whether replacing half of the rice in a given meal with either of the two oat grains could make a difference in acute glycaemic responses. METHODS: In a randomised crossover trial, ten healthy subjects consumed two groups of test meals: (1) oat grain-only, including whole grain oats cooked under normal pressure (WONP) and higher pressure (WOHP) as well as their pearled oat counterparts, PONP and POHP; and (2) mixed meals of aforementioned oat grains and cooked rice (OG + R), including WONP + R, WOHP + R, PONP + R and POHP + R. A postprandial blood glucose test, texture profile analysis and in vitro carbohydrate digestion assay were carried out for each test meal. RESULTS: Compared with the rice reference, oat grain-only meals induced lower glucose levels at all time points, lower peak values and smaller glucose excursions at 120 min (P < 0.05), but OG + Rs did not have the abovementioned effects. The oat grain-only meals had glycaemic indexes (GIs) ranging from 51 to 58, while those of OG + Rs ranged from 59 to 70. WONP + R had a 21% lower iAUC0-60 and a 40% lower iAUC60-120 value than those of rice (P < 0.05). Oat-rice mixed meals had lower iAUC0-60 values compared with that of the rice control (P < 0.05), except for POHP + R. Excellent consistency between the hydrolysis index and the GI was observed (r = 0.969, P < 0.001) in oat grain-only meals. CONCLUSIONS: All oat grain-only meals could be included in the glycaemic management diet, regardless of the oat grain type or cooking treatment. In oat-rice mixed meals, whole grain oats and normal pressure cooking ensured a favourable glycaemic effect.

Acute effects of non-homogenised and homogenised vegetables added to rice-based meals on postprandial glycaemic responses and in vitro carbohydrate digestion.

The addition of vegetable to carbohydrate-based meals was shown to contribute to glycaemic management. The aim of this study was to investigate the impact of homogenisation on vegetables added to rice meals in terms of acute glycaemic responses (GR). In a randomised crossover trial, sixteen healthy volunteers completed thirteen test sessions, which included two sessions for glucose control, two for rice and nine for different vegetable-rice mixed meals: cooked pak choi and cooked rice (CP+R); cooked cauliflower and cooked rice (CC+R); cooked eggplant and cooked rice (CE+R); and their homogenised counterparts, both raw or cooked. Postprandial GR tests, in vitro carbohydrate digestion and chemical analyses were carried out for each test meal. Compared with pure rice, CE+R, CP+R and CC+R meals achieved significantly lower glycaemic indexes (GI) of 67, 71 and 73, whereas their homogenised counterparts failed to show significant difference with rice. The hydrolysis indexes (HI) of CE+R, CP+R and CC+R were 69·6, 83·8 and 80·6 % of the HI of the rice control. CE had the greatest effect on lowering the GI, the incremental area under the blood glucose curve from 0 to 120 min, the peak glucose value, the maximum amplitude of glucose excursion in 0-120 min (MAGE0 -120), the HI and rapid available starch. Both in vitro and in vivo tests demonstrated that incorporating non-homogenised cooked vegetables into a rice meal could slow the carbohydrate digestion and improve postprandial GR. Texture properties of vegetable may play an important role in underlying glycaemic control mechanisms.

Efficacy of fibre additions to flatbread flour mixes for reducing post-meal glucose and insulin responses in healthy Indian subjects.

The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide, including in developing countries, particularly in South Asia. Intakes of foods generating a high postprandial glucose (PPG) response have been positively associated with T2DM. As part of efforts to identify effective and feasible strategies to reduce the glycaemic impact of carbohydrate-rich staples, we previously found that addition of guar gum (GG) and chickpea flour (CPF) to wheat flour could significantly reduce the PPG response to flatbread products. On the basis of the results of an exploratory study with Caucasian subjects, we have now tested the effect of additions of specific combinations of CPF with low doses of GG to a flatbread flour mix for their impacts on PPG and postprandial insulin (PPI) responses in a South-Asian population. In a randomised, placebo-controlled full-cross-over design, fifty-six healthy Indian adults consumed flatbreads made with a commercial flatbread mix (100 % wheat flour) with no further additions (control) or incorporating 15 % CPF in combination with 2, 3 or 4 % GG. The flatbreads with CPF and 3 or 4 % GG significantly reduced PPG (both ≥15 % reduction in positive incremental AUC, P<0·01) and PPI (both ≥28 % reduction in total AUC, P<0·0001) compared with flatbreads made from control flour. These results confirm the efficacy and feasibility of the addition of CPF with GG to flatbread flour mixes to achieve significant reductions in both PPG and PPI in Indian subjects.

Decreasing the RAG:SAG ratio of granola cereal predictably reduces postprandial glucose and insulin responses: a report of four randomised trials in healthy adults.

Dietary starch contains rapidly (RAG) and slowly available glucose (SAG). To establish the relationships between the RAG:SAG ratio and postprandial glucose, insulin and hunger, we measured postprandial responses elicited by test meals varying in the RAG:SAG ratio in n 160 healthy adults, each of whom participated in one of four randomised cross-over studies (n 40 each): a pilot trial comparing six chews (RAG:SAG ratio 2·4-42·7) and three studies comparing a test granola (TG1-3, RAG:SAG ratio 4·5-5·2) with a control granola (CG1-3, RAG:SAG ratio 54·8-69·3). Within studies, test meals were matched for fat, protein and available carbohydrate. Blood glucose, serum insulin and subjective hunger were measured for 3 h. Data were subjected to repeated-measures analysis of variance (ANOVA). The relationships between the RAG:SAG ratio and postprandial end points were determined by regression analysis. In the pilot trial, 0-2 h glucose incremental areas under the curve (iAUC0-2; primary end point) varied across the six chews (P = 0·014) with each 50 % reduction in the RAG:SAG ratio reducing relative glucose response by 4·0 %. TGs1-3 elicited significantly lower glucose iAUC0-2 than CGs1-3 by 17, 18 and 17 %, respectively (similar to the 15 % reduction predicted by the pilot trial). The combined means ± sem (n 120) for TC and CG were glucose iAUC0-2, 98 ± 4 v. 118 ± 4 mmol × min/l (P < 0·001), and insulin iAUC0-2, 153 ± 9 v. 184 ± 11 nmol × h/l (P < 0·001), respectively. Neither postprandial hunger nor glucose or hunger increments 2 h after eating differed significantly between TG and CG. We concluded that TGs with RAG:SAG ratios <5·5 predictably reduced glycaemic and insulinaemic responses compared with CGs with RAG:SAG ratios >54. However, compared with CG, TG did not reduce postprandial hunger or delay the return of glucose or hunger to baseline.

Beta-glucans from oats and/or barley in a ready-to-eat cereal manufactured via pressure cooking and reduction of blood-glucose rise after consumption: evaluation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006.

Following an application from Nestlé S.A. submitted for authorisation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of Belgium, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to beta-glucans from oats and/or barley in a ready-to-eat cereal manufactured via pressure cooking and reduction of blood glucose rise after consumption. The scope of the application was proposed to fall under a health claim based on newly developed scientific evidence. The food proposed is 'beta-glucans from oats and/or barley incorporated into ready-to-eat breakfast cereals manufactured via pressure cooking'. The applicant proposed that at least 1.3 g of beta-glucans/25 g of available carbohydrates in ready-to-eat breakfast cereals manufactured via pressure cooking should be consumed. Beta-glucans from oats, barley or any combination thereof incorporated into ready-to-eat cereals manufactured by pressure cooking, are sufficiently characterised. The claimed effect proposed is 'reduction of the blood glucose rise after the meal'. The reduction of post-prandial glycaemic responses (as long as post-prandial insulinaemic responses are not disproportionally increased) may be a beneficial physiological effect. One human intervention study showed an effect of beta-glucans from oats and/or barley, incorporated into breakfast cereals manufactured via pressure cooking at a level of at least 1.2 g/25 g available carbohydrates, on decreasing post-prandial glycaemic responses without disproportionally increasing insulinaemic responses. Dose-response relationships were not tested, and no evidence has been provided that beta-glucans incorporated into cereals processed using pressure cooking would exert a higher effect on post-prandial glucose responses than beta-glucans added to other carbohydrate containing foods. Whereas the effect of beta-glucans in reducing post-prandial blood glucose responses is well established, the evidence provided is insufficient to establish such an effect at doses of 1.3 g beta-glucans per 25 g of available carbohydrate incorporated into ready-to-eat breakfast cereals manufactured via pressure cooking (i.e. either batch cooking or extrusion).

Postprandial Glycaemic Responses of Dried Fruit-Containing Meals in Healthy Adults: Results from a Randomised Trial.

The aim of this study was to explore the glycaemic response (GR) patterns of four dried fruits (DF) and the mixed meals containing dried fruits, rice and almonds. Dried apples (DApp), dried jujubes (DJ), raisins (Ra) and dried apricots (DApr) were tested in eleven healthy subjects in random order. Test meals included the following 3 groups: (1) dried fruits containing 50 g available carbohydrates; (2) mixed meals consisting of DF and rice (DF + R), each contributing 25 g available carbohydrates; (3) Group (2) supplemented with 30 g almonds (DF + R + A). The postprandial GR and other characteristics in 240 min were investigated. The GI values of 4 DFs were 43 for DApp, 55 for DJ, 56 for both Ra and DApr. The DApp displayed the smallest amplitude of glycaemic excursion within 240 min (MAGE0⁻240). Compared with rice, the DApp + R meal elicited a significantly reduced GR and a smaller MAGE0⁻240 (GI 81 vs. 65). With the addition of almonds, the GIs and MAGE0⁻240 decreased significantly in all DF + A + R combinations except DApp + R + A. The ratio of total fructose/glucose contents of test meals were negatively correlated to GIs. Dried fruits and nuts may have the potential to mitigate the postprandial GR when jointly introduced into glycaemic management diets.