Article

Effect of coffee and tea on the glycaemic index of foods: No effect on mean but reduced variability

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Abstract

Coffee and tea may influence glycaemic responses but it is not clear whether they affect the glycaemic index (GI) value of foods. Therefore, to see if coffee and tea affected the mean and SEM of GI values, the GI of fruit leather (FL) and cheese puffs (CP) were determined twice in ten subjects using the FAO/WHO protocol with white bread as the reference food. In one series subjects chose to drink 250 ml of either coffee or tea with all test meals, while in the other series they drank 250 ml water. The tests for both series were conducted as a single experiment with the order of all tests being randomised. Coffee and tea increased the overall mean peak blood glucose increment compared with water by 0.25 (SEM 0.09) mmol/l (P=0.02), but did not significantly affect the incremental area under the glucose response curve. Mean GI values were not affected by coffee or tea but the SEM was reduced by about 30% (FL: 31 (SEM 4) v. 35 (SEM 7) and CP: 76 (SEM 6) v. 75 (SEM 8) for coffee or tea v. water, respectively). The error mean square term from the ANOVA of the GI values was significantly smaller for coffee or tea v. water (F(18, 18) = 2.31; P=0.04). We conclude that drinking coffee or tea with test meals does not affect the mean GI value obtained, but may reduce variability and, hence, improve precision.

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... In another study, the co-ingestion of unsweetened CC (or tea), instead of water, with a standardized test meal resulted in a significantly greater glucose concentration at t 45 min, but with no effect on the incremental AUC for blood glucose ( Young and Wolever, 1998). CC or tea co-ingested with either white bread or cheese puffs (high-GI) also resulted in a significant increase in blood glucose concentration after 30 min as compared to the same meals with water ( Aldughpassi and Wolever, 2009), but this difference was not observed when fruit leather (low-GI) was used as test meal. For all three meals, the incremental AUC for blood glucose concentration did not differ between CC or tea and water. ...
... All of the studies that reported a significant effect of drip-filtered CC or tea on blood glucose concentration (and sometimes, but not always, on the IAUC of glycemic response) used a high-GI meal as the carbohydrate load, either a solid food, or liquid glucose (GI 100), i.e. an oral glucose tolerance test. Also, CC or tea was co-ingested with the meal ( Aldughpassi and Wolever, 2009;Johnston et al., 2003;Moisey et al., 2009;Young and Wolever, 1998). In contrast to these studies, we used a medium-GI meal (mankoucheh), i.e. one producing a lower overall glycemic response in comparison with high-GI foods. ...
... In contrast to these studies, we used a medium-GI meal (mankoucheh), i.e. one producing a lower overall glycemic response in comparison with high-GI foods. The only study that used a low-GI food (fruit leather, GI value around 35) co-ingested with drip-filtered CC or tea found no difference in blood glucose concentrations and corresponding IAUC compared to the same food ingested with water ( Aldughpassi and Wolever, 2009). When the same experiment was conducted with high-GI foods (cheese puffs and white bread), postprandial blood glucose was significantly increased at time 30 min for CC versus water ( Aldughpassi and Wolever, 2009). ...
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Purpose: The aim of this study was to evaluate the individual effect of sumac (S), Turkish coffee (C) and yerba mate tea (Y) on the postprandial glycemic response to Lebanese mankoucheh, a common breakfast item in the Lebanese culture, and to determine the glycemic index (GI) of this food. S, C and Y are typical constituents of Lebanese meals. They may influence the postprandial glycemic response to carbohydrate-rich foods, but this has not been studied to date. Design/methodology/approach: Twelve healthy normoglycemic adults consumed on separate days the following test meals: mankoucheh without S (M) with water (control meal); M prepared with single or double doses of S (S1 and S2) with water; M with 60 or 120 mL of unsweetened C; or M with 100 or 200 mL of unsweetened Y. Meals were prepared according to standardized recipes containing 50 g of available carbohydrates. Capillary blood glucose measures were taken at fast and six times after meal ingestion over a two hour period. The GI of mankoucheh was determined using a standard protocol. Findings: The glycemic responses, evaluated at each time following meal ingestion, did not differ significantly among the seven meals, and neither did the incremental area under the glycemic response curves. The GI of mankoucheh was 61 ± 6, with no significant difference between M, M with S1 and M with S2. Originality/value: This study contributes to better characterize the glycemic properties of S, C, Y and mankoucheh in conditions that closely resemble how these dietary items are used and consumed by some cultural groups.
... GTE at the levels of 0.4% or at high dose (3 capsules equivalent to 3.5 cups) was not associated with a reduced postprandial glucose response (Venables et al., 2008;Coe and Ryan 2016). Another one study showed how tea intake as a beverage had no effect on postprandial glucose response (Louie et al., 2008;Aldughpassi et al., 2008). These studies differed in brewing time (30 seconds to 3 min), and this time might be too short to efficiently extract the (poly)phenols (Sandip et al., 2013). ...
... A higher score indicates a higher degree of acceptability of the breads. The raw data for palatability was translated and presented as a star diagram (British Nutrition Foundation, 2016a; Aldughpassi et al., 2008;Finocchiaro et al., 2012). ...
... Secondly, tea (poly)phenols reached their maximum plasma concentration between 0.8 to 2.3 h after intake of 300 -500 mL green tea (Stalmach et al., 2009;Stalmach et al., 2010). This may have beneficial effects on plasma glucose, as the peak postprandial glucose response occurred at 30 min after an oral glucose tolerance test (Aldughpassi et al., 2008;Louie et al., 2008). However, as discussed in Section 1.8.3 (Table 1-12), only one out of four studies showed that black tea reduced postprandial glucose response. ...
... Coffee has attracted considerable attention in the field of nutritional sciences, where an increasing body of evidence supports a protective role of habitual consumption on risk factors of non-communicable diseases, namely type 2 diabetes [1,2]. There has been much debate, however, over the effect of coffee on glucose and insulin responses, with some studies suggesting no postprandial changes [3][4][5][6], whereas others report significant increases in postprandial glycemic and insulinemic responses [7,8]. Coffee contains numerous bioactive compounds that may influence glucose and insulin homeostasis, including chlorogenic acid [9] and quinides [10], as well as the mineral magnesium [11]. ...
... The effects of caffeinated coffee on glycemic and insulinemic changes following a carbohydrate meal have found conflicting results, with some studies suggesting no postprandial effects [3,5], whereas others find significant glycemic and insulinemic responses to caffeinated coffee [8,26]. Other human studies investigating the acute effect of caffeine administration on glucose and insulin changes following a glucose solution have found similar adverse glycemic and insulinemic responses [12][13][14]. ...
... We allowed subjects to drink water, coffee or tea with the test meals, which might be thought to introduce betweensubject variation and, hence, be a flaw in the study design. However, we do not believe this to be a problem because, compared with drinking water, coffee and tea have no significant effect on AUC (Young and Wolever, 1998) or GI (Aldughpassi and Wolever, 2009) and may actually reduce variation in GI (Aldughpassi and Wolever, 2009). ...
... We allowed subjects to drink water, coffee or tea with the test meals, which might be thought to introduce betweensubject variation and, hence, be a flaw in the study design. However, we do not believe this to be a problem because, compared with drinking water, coffee and tea have no significant effect on AUC (Young and Wolever, 1998) or GI (Aldughpassi and Wolever, 2009) and may actually reduce variation in GI (Aldughpassi and Wolever, 2009). ...
Article
Glycaemic responses are influenced by carbohydrate absorption rate, type of monosaccharide absorbed and the presence of fat; the effect of some of these factors may be modulated by metabolic differences between subjects. We hypothesized that glycaemic index (GI) values are affected by the metabolic differences between subjects for foods containing fructose or fat, but not for starchy foods. The GI values of white bread (WB), fruit leather (FL) and chocolate-chip cookies (CCC) (representing starch, fructose and fat, respectively) were determined in subjects (n=77) recruited to represent all 16 possible combinations of age (< or =40, >40 years), sex (male, female), ethnicity (Caucasian, non-Caucasian) and body mass index (BMI) (< or =25, >25 kg/m2) using glucose as the reference. At screening, fasting insulin, lipids, c-reactive protein (CRP), aspartate transaminase (AST) and waist circumference (WC) were measured. There were no significant main effects of age, sex, BMI or ethnicity on GI, but there were several food x subject-factor interactions. Different factors affected each food's area under the curve (AUC) and GI. The AUC after oral glucose was related to ethnicity, age and triglycerides (r 2=0.27); after WB to ethnicity, age, triglycerides, sex and CRP (r 2=0.43); after CCC to age and weight (r 2=0.18); and after FL to age and CRP (r 2=0.12). GI of WB was related to ethnicity (r 2=0.12) and of FL to AST, insulin and WC (r 2=0.23); but there were no significant correlations for CCC. The GI values of foods containing fructose might be influenced by metabolic differences between -subjects, whereas the GI of starchy foods might be affected by ethnicity. However, the proportion of variation explained by subject factors is small.
... Study methodology quality was assessed for each trial comparison based on eleven predetermined criteria outlined in Supplementary Table 2 which was adapted from a previous study [11,16]. This assessment identified protocol components that have been established as significant determinants of the accuracy and precision of PPGR measurements [17][18][19][20][21][22][23][24][25][26][27][28]. The score was used to inform the responses to the signalling questions in the "bias in measurement of the outcome" domain of the RoB 2 tool and to determine the influence of study methodology quality in the relationship between OBG and PPGR. ...
Article
Objectives The efficacy of oat beta-glucan (OBG), a viscous soluble fibre, on postprandial glycemic outcomes may depend on the nature of the control and the dose and molecular weight (MW) utilized. We undertook a systematic review and meta-analysis of acute clinical trials to determine whether these features mediate the glycemic response to OBG. Methods MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched through October 2, 2019. We included acute, single-meal feeding, controlled trials investigating the effect of OBG (concentrate or oat bran) added to a carbohydrate-containing meal compared to a comparable meal (matched control) or a different carbohydrate-containing meal (unmatched control). Two reviewers extracted the data and assessed the risk of bias. The primary outcome was incremental area under the curve (iAUC) for blood glucose. Data were pooled using the generic-inverse variance method with random effects model and expressed as ratio of means with [95% Cis]. Results We included 93 trial comparisons (N = 432). OBG reduced glucose iAUC by 23% (0.77 [0.73 to 0.81]). The effect was not significantly different between matched and unmatched controls (P = 0.17). Dose and MW were significant effect modifiers (P < 0.01). OBG doses per 30 g available carbohydrate of <1.5 g, 1.5 to <2.5 g, 2.5 to <3.5 g, 4.5 to <5.5 g, and >5.5 g OBG led to reductions of 9% (0.91 [0.81 to 1.02]), 14% (0.86 [0.80 to 0.93]), 17% (0.83 [0.76 to 0.90]), 31% (0.69 [0.64 to 0.74)], and 39% (0.61 [0.56 to 0.66]), respectively. Low MW OBG (<300,000 g/mol) had no effect (1.00 [0.94 to 1.07]) but medium MW (300,000 to <1000,000 g/mol) and high MW (>1000,000 g/mol) OBG led to significant reductions of 23% (0.77 [0.69 to 0.87]) and 32% (0.68 [0.63 to 0.73]), respectively. Conclusions Current evidence indicates that the addition of oat beta-glucan to carbohydrate-containing meals reduces the postprandial glycemic response. However, the magnitude of the reduction depends on the dose and the molecular weight of the oat beta-glucan. Funding Sources INQUIS Clinical Research Ltd. (formerly GI Labs), and PepsiCo Global R&D.
... In the current study, the snacks were consumed with tea; however, it is unlikely that consumption of tea have affected the glycemic responses. In previous studies, consumption of tea or coffee did not affect GI of foods though it reduced within-individual variability in blood glucose and thus lowered standard deviation (32). ...
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Background and Objectives: Snacks are important parts of diabetes patients’ diet. The aim of the present study was to evaluate the effects of moderate amounts of dates and raisins, as nutritious snacks, on blood glucose, and to compare these effects with sugar in patients with type 2 diabetes. Materials and Methods: This crossover clinical trial was performed on 15 patients with type 2 diabetes. In each experimental day, fasting blood glucose (FBG) was initially measured, and a breakfast containing 90 g bread was consumed. Two hours later, blood glucose was measured. Then a snack containing 15 g available carbohydrate from dates, raisins, or sugar was given, and postprandial blood glucose was measured at 30, 60, and 120 min. The procedure was performed on 3 days, each day with one of the aforementioned snacks. Comparisons between the different snacks were done with the Friedman’s test. Results: Consumption of dates, raisins, or sugar did not increase blood glucose (alterations in blood glucose at 30 min compared to the time point before snack consumption were -2.23 ± 32.0, -6.33 ± 24.3, and -2.30 ± 16.9 for dates, raisins, and sugar, respectively), and there was no significant difference between the snacks in blood glucose levels at any time point after their consumption, and also in the area under the curve of blood glucose alterations. Conclusions: In moderate quantities, the effects of dates, raisins and sugar on the blood glucose of diabetes patients were similar. However, considering their nutrient content, dates and raisins may be more suitable snacks than sugar for patients with type 2 diabetes. Keywords: Type 2 diabetes, Dates, Raisins, Sugar, Blood glucose
... on the endpoint (e.g., PR, AUC, RGR). We used finger-prick capillary rather than venous blood sampling [9] and allowed subjects to drink coffee or tea with the test meal [10] because these procedures did not affect the mean but decreased within-individual variation of GI. Because methodologic variation may influence the results obtained, it is important to clearly describe the methods used when publishing the results of postprandial testing. ...
Article
The blood glucose responses elicited by foods are often determined using blood samples taken at 15-min intervals. Our objective was to see whether taking blood samples at 10-min intervals affected the results. Overnight-fasted healthy subjects (n=11) were studied on nine different occasions with seven different test meals. Blood samples were obtained at fasting and at 10, 15, 20, 30, 40, 45, 50, 60, 90, and 120 min after starting to eat. Peak rise, incremental area under the curve, and relative glycemic response were calculated using the 10- and 15-min sampling schedules. With 10-min intervals, peak rise was 4% greater than with 15-min intervals (P<0.001), but sampling interval did not significantly affect mean incremental area under the curve or relative glycemic response. The 10-min blood sampling schedule had a slightly greater ability to discriminate between foods and between subjects for peak rise and relative glycemic response. We conclude that the blood sampling schedule used may influence the accuracy and precision of measurements of glycemic response; however, the difference between taking blood samples at 10-min and 15-min intervals is quite small.
... Caffeine in coffee and tea may increase the glucose responses (32 -35) and decrease insulin sensitivity (32) . However, in our previous study, coffee modified postprandial glucose and insulin responses only modestly (unpublished results), an observation that is consistent with the study of Aldughpassi & Wolever (36) . Therefore, it is unlikely that the drink served influenced the results. ...
Article
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The beneficial effects of a low-glycaemic index (GI) meal on postprandial glucose and insulin levels have been demonstrated. However, limited data are available on the impact of overweight and glucose tolerance on postprandial responses to different GI meals. Our aim was to study the effects of physiological characteristics on postprandial glucose, insulin and lipid responses and the relative glycaemic response (RGR) of a low-GI (LGI) and a high-GI (HGI) meal. We recruited twenty-four normal-weight and twenty-four overweight subjects, twelve with normal glucose tolerance (NGT) and twelve with impaired glucose tolerance (IGT) in each group. Both test meals were consumed once and the glucose reference twice. Blood glucose and insulin were measured in the fasting state and over a 2 h period after each study meal, and TAG and NEFA were measured in the fasting state and over a 5 h period. The glucose responses of subjects with IGT differed significantly from those of subjects with NGT. The highest insulin responses to both meals were observed in overweight subjects with IGT. Physiological characteristics did not influence TAG or NEFA responses or the RGR of the meals. The LGI meal resulted in lower glucose (P < 0·001) and insulin (P < 0·001) responses, but higher TAG responses (P < 0·001), compared with the HGI meal. The GI of the meals did not affect the NEFA responses. In conclusion, the LGI meal causes lower glucose and insulin responses, but higher TAG responses, than the HGI meal. The RGR of the meals does not differ between normal-weight and overweight subjects with NGT or IGT.
... Only, a few studies have focused upon how caffeine in a coffee drink affects postprandial glucose and insulin responses, and the published findings are inconsistent. Some studies suggest that coffee does not significantly affect 2-h postprandial glucose responses in healthy subjects [3,[10][11][12], whereas some studies report that coffee significantly increases postprandial glycaemia and insulinaemia both in healthy subjects [13] and in subjects with type 2 diabetes [14]. ...
Article
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Strong epidemiological evidence suggests that coffee consumption is associated with lower risk of type 2 diabetes. In postprandial studies, however, caffeine consumption has been associated with impaired glucose regulation. To study the acute effects of coffee and caffeine-containing soft drinks on glycaemic and insulinaemic responses. Twelve healthy volunteers were served each test food once and the reference glucose solution twice, containing 50 g of available carbohydrates, after an overnight fast at 1-week intervals in a random order. Capillary blood samples were drawn at 15-30 min intervals for 2 h after each study meal. The incremental areas under the curve (IAUC), glycaemic index (GI) and insulinaemic index (II), were calculated to estimate the glycaemic and insulinaemic responses. Glucose and insulin responses of coffees with glucose containing 150 or 300 mg of caffeine did not differ from responses of pure glucose solution; the GIs were 104 and 103, and the IIs were 89 and 92, respectively. When a bun or sucrose and milk were consumed together with coffee, lower GI values and insulin responses were observed, reflecting the carbohydrate quality and protein content of the accompaniments. Sucrose-sweetened cola produced a high GI value of 90 and an II of 61. Coffee does not modify glycaemic and insulinaemic responses when ingested with a carbohydrate source. Therefore, there is no need to avoid coffee as a choice of beverage in GI testing.
... Black tea has been shown to decrease plasma glucose and enhance insulin concentrations after consumption in comparison to a control and a caffeine drink [10]. Aldughpassi and Wolever [11] showed that 250 mL of black tea with test meals actually increased overall mean peak BG compared to water though a reduction in the standard error might indicate the ability of tea compounds to improve the precision of the BG response. A study of green tea catechins in insulin resistant induced obese rats suggested that they may impact glucose control through several pathways [12]. ...
Article
Full-text available
Tea (Camellia sinensis) is a widely consumed beverage and recognised for its potential enhancing effect on human health due to its rich polyphenol content. While a number of studies have investigated the quantity and type of polyphenols present in different tea samples, no study has reported the potential effect of digestive enzymes on the availability of tea polyphenols for human absorption or the subsequent impact on glycaemic response. The objectives of the present study were to assess the total polyphenol content of different teas, to assess the bioaccessibility of polyphenols in whole and bagged teas, and to determine the effect of black, white, and green tea infusions on sugar release. All of the teas were a significant source of polyphenols (10–116 mg Gallic acid equivalents/g). There was an overall increase in the release of polyphenols from both the bagged and the whole teas following in vitro digestion. Bagged green tea significantly () reduced rapidly digestible starch from white bread samples compared to control and black and white bagged teas. The present study confirms that tea is a rich source of polyphenols and highlights the potential benefits it may have on modulating glycaemic response in humans.
... In addition, the caffeine present in the sugar-sweetened cola may influence the glycaemic response to carbohydrates. Though some evidence has shown reduced insulin sensitivity (Shi et al. 2016) and increased glycaemia (Moisey et al. 2008) with caffeine ingestion, other studies have found no effects of caffeine on the glycaemic response to food (Aldughpassi and Wolever 2009) or to a glucose drink (H€ at€ onen et al. 2012). Caffeine-free diet cola was selected to minimise influences that might confound the glycaemic effects of the NNS present. ...
Article
Substituting sugar-sweetened for artificially sweetened beverages may reduce energy intakes. This study aims to ascertain the acute glycaemic effects of the NNS aspartame and acesulfame-K in UK diet-cola (DC). Ten healthy participants attended the laboratory fasted on three occasions. Individuals drank (1) 25 g glucose in 125 mL water + 236 mL water, (2) 25 g glucose in 125 mL water with 236 mL DC and (3) 236 mL sucrose-sweetened cola with 125 mL water. Blood (glucose) was measured pre-test and every 15 minutes over a 120-minute period using portable glucometers. The glucose-control and glucose + DC elicited similar blood glucose rises above pre-prandial levels. Sucrose-sweetened cola showed a non-significant lower rise in postprandial glycaemia, exhibiting the lowest glycaemic index (GI) (77.0 ± 9.1). GI of glucose (100.0 ± 15.2) and glucose + DC (104.3 ± 8.5) was similar and a one-way repeated-measures ANOVA showed no significant differences in glycaemic response between test drinks (F(2,29) = 1.68, p > .05). Results demonstrate the glycaemic inactivity of non-nutritive sweeteners.
... 80,81 In contrast, other investigators failed to detect an effect of acute coffee intake on these glucose metabolism markers. 176,177 Although results of the effect of coffee on diabetes are not always clear-cut, and some intervention and epidemiological studies have revealed no effect, most of the more recent studies observed a signicant risk reduction of 30-60%, in the same range as observed with pharmacological approaches. 166 Nevertheless, until the relationship between long-term coffee consumption and type 2 DM is better understood and any mechanism involved identied, it is premature to make claims about coffee preventing type 2 DM. ...
Article
This review provides details on the phytochemicals in green coffee beans and the changes that occur during roasting. Key compounds in the coffee beverage, produced from the ground, roasted beans, are volatile constituents responsible for the unique aroma, the alkaloids caffeine and trigonelline, chlorogenic acids, the diterpenes cafestol and kahweol, and melanoidins, which are Maillard reaction products. The fate of these compounds in the body following consumption of coffee is discussed along with evidence of the mechanisms by which they may impact on health. Finally, epidemiological findings linking coffee consumption to potential health benefits including prevention of several chronic and degenerative diseases, such as cancer, cardiovascular disorders, diabetes, and Parkinson's disease, are evaluated.
... Study methodology quality was assessed for each trial comparison based on eleven predetermined criteria outlined in Supplementary Table 2 which was adapted from a previous study [11,16]. This assessment identified protocol components that have been established as significant determinants of the accuracy and precision of PPGR measurements [17][18][19][20][21][22][23][24][25][26][27][28]. The score was used to inform the responses to the signalling questions in the "bias in measurement of the outcome" domain of the RoB 2 tool and to determine the influence of study methodology quality in the relationship between OBG and PPGR. ...
Article
Full-text available
To determine the effect of oat β‑glucan (OBG) on acute glucose and insulin responses and identify significant effect modifiers we searched the MEDLINE, EMBASE, and Cochrane databases through October 27, 2020 for acute, crossover, controlled feeding trials investigating the effect of adding OBG (concentrate or oat-bran) to carbohydrate-containing test-meals compared to comparable or different carbohydrate-matched control-meals in humans regardless of health status. The primary outcome was glucose incremental area-under-the-curve (iAUC). Secondary outcomes were insulin iAUC, and glucose and insulin incremental peak-rise (iPeak). Two reviewers extracted the data and assessed risk-of-bias and certainty-of-evidence (GRADE). Data were pooled using generic inverse-variance with random-effects model and expressed as ratio-of-means with [95% CIs]. We included 103 trial comparisons ( N = 538). OBG reduced glucose iAUC and iPeak by 23% (0.77 [0.74, 0.81]) and 28% (0.72 [0.64, 0.76]) and insulin by 22% (0.78 [0.72, 0.85]) and 24% (0.76 [0.65, 0.88]), respectively. Dose, molecular-weight, and comparator were significant effect modifiers of glucose iAUC and iPeak. Significant linear dose-response relationships were observed for all outcomes. OBG molecular-weight >300 kg/mol significantly reduced glucose iAUC and iPeak, whereas molecular-weight <300 kg/mol did not. Reductions in glucose iAUC (27 vs 20%, p = 0.03) and iPeak (39 vs 25%, p < 0.01) were significantly larger with different vs comparable control-meals. Outcomes were similar in participants with and without diabetes. All outcomes had high certainty-of-evidence. In conclusion, current evidence indicates that adding OBG to carbohydrate-containing meals reduces glycaemic and insulinaemic responses. However, the magnitude of glucose reduction depends on OBG dose, molecular-weight, and the comparator.
... Furthermore, factors known to create bias or increase random error in the results of GI testing are not among the criteria used to judge the quality of clinical trials, namely: the number of subjects, 28 blood sampling schedule, 29 the precision of the glucose analytical method, 4,30 the precision of the measure of fasting glucose, 4,31 the number of reference food tests, 4,32 within subject variation of AUC elicited by the reference food, 4 subject preparation, 4,33 the amount of available carbohydrate fed to subjects, 28 food composition 34 and the nature of the drink consumed with the test meals. 4,35 Our GI methodological quality assessment did not include an assessment of randomization. As GI testing involves multiple treatments taken by each subject over a period of time, formal randomization of the order of treatments may not be desirable or ideal. ...
Article
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Objectives: Low glycaemic index (GI) foods are recommended to improve glycaemic control in diabetes; however, Health Canada considers that GI food labeling would be misleading and unhelpful, in part, because selected studies suggest that GI values are inaccurate due to an effect of ethnicity. Therefore, we conducted a systematic review and meta-analysis to compare the GI of foods when measured in Caucasians versus non-Caucasians. Methods: We searched MEDLINE, EMBASE and Cochrane databases for relevant articles. GI differences were aggregated using the generic inverse variance method (random effects model) and expressed as mean difference (MD) with 95% confidence intervals (95% CI). Study quality was assessed based on how well studies complied with official international GI methodology. Results: Review of 1288 trials revealed eight eligible studies, including 28 comparisons of GI among 585 non-Caucasians and 971 Caucasians. Overall, there was borderline significant evidence of higher GI in non-Caucasians than Caucasians (MD, 3.3 (95% CI, -0.1, 6.8); P=0.06) with significant heterogeneity (I(2), 46%; P=0.005). The GI of eight types of rice was higher in non-Caucasians than Caucasians (MD, 9.5 (95% CI, 3.7, 23.1); P=0.001), but there was no significant difference for the other 20 foods (MD, 1.0 (95% CI, -2.5, 4.6); P=0.57). MD was significantly greater in the four low-quality studies (nine comparisons) than the four high-quality studies (19 comparisons; 7.8 vs 0.7, P=0.047). Conclusions: With the possible exception of rice, existing evidence suggests that GI values do not differ when measured in Caucasians versus non-Caucasians. To confirm these findings high-quality studies using a wide range of foods are required.
... Studies examining the effect of coffee on glucose metabolism have reported controversial results. Whereas some studies, like ours, found similar glucose and insulin responses 2-3 h after consumption of either regular coffee or water (33)(34)(35)(36)(37)(38)(39) , others showed increased 2-h glucose and insulin AUC for regular coffee compared with either water (40) or decaffeinated coffee (13,40,41) . Moreover, two studies reported a lower glucose AUC for decaffeinated coffee compared with regular coffee (42) or water (43) . ...
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Epidemiological studies have found coffee consumption is associated with a lower risk for type 2 diabetes mellitus, but the underlying mechanisms remain unclear. Thus, the aim of this randomised, cross-over single-blind study was to investigate the effects of regular coffee, regular coffee with sugar and decaffeinated coffee consumption on glucose metabolism and incretin hormones. Seventeen healthy men participated in five trials each, during which they consumed coffee (decaffeinated, regular (containing caffeine) or regular with sugar) or water (with or without sugar). After 1 h of each intervention, they received an oral glucose tolerance test with one intravenous dose of [1- ¹³ C]glucose. The Oral Dose Intravenous Label Experiment was applied and glucose and insulin levels were interpreted using a stable isotope two-compartment minimal model. A mixed-model procedure (PROC MIXED), with subject as random effect and time as repeated measure, was used to compare the effects of the beverages on glucose metabolism and incretin parameters (glucose-dependent insulinotropic peptide (GIP)) and glucagon-like peptide-1 (GLP-1)). Insulin sensitivity was higher with decaffeinated coffee than with water ( P <0·05). Regular coffee with sugar did not significantly affect glucose, insulin, C-peptide and incretin hormones, compared with water with sugar. Glucose, insulin, C-peptide, GLP-1 and GIP levels were not statistically different after regular and decaffeinated coffee compared with water. Our findings demonstrated that the consumption of decaffeinated coffee improves insulin sensitivity without changing incretin hormones levels. There was no short-term adverse effect on glucose homoeostasis, after an oral glucose challenge, attributable to the consumption of regular coffee with sugar.
... It was noted that Khalas date meal was significantly better in terms of maintaining glycaemic index (57.7 mg/dL vs. 79.0 mg/dL) because it contains fructose as well as fibres [73]. Therefore, the study concluded that date meal is a beneficial diet for diabetic subjects as compared to conventional Saudi breakfast. ...
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Diabetes is a chronic metabolic disorder triggered by disturbances in carbohydrate, protein, and lipid metabolisms, where either reduced secretion or sensitivity of insulin is observed coupled with poor glucose control. Date palm fruits are one of the fruits reported to have good potential in diabetes treatment due to its presence of polyphenols exerting strong antioxidant activities. Other possible mechanisms of action include the polyphenolic compounds, which can inhibit enzymes like α-amylase and α-glucosidase. Flavonoids in dates can stimulate β-cells by increasing the number of islets and β-cells, recovering endocrine pancreatic tissues, reducing β-cell apoptosis, activating insulin receptors following the increase in insulin secretion, in addition to improving diabetes-induced complications. In this review, the in vitro, in vivo, and human study-based evidence of date palm as an anti-diabetic fruit is summarised.
... An early study suggested that CV within of glucose iAUC is highest in type 1 diabetes, intermediate in subjects without diabetes and lowest in subjects with T2D [48]. Also, it has been suggested that CV within is: high with avCHO intakes <20 g [49]; lower with capillary versus venous blood sampling [18,50]; reduced by consuming coffee or tea with the test meal versus water [51]; high when glucose is measured using a method with low analytical precision [52,53]; and not reduced by controlling subject fasting time, providing a standard dinner and prohibiting vigorous exercise the previous day [54]. However, the effect of these procedures on CV within is not always seen [47]. ...
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To determine the minimum amount of oat β-glucan (OBG) required to reduce glycaemic responses (MinDose), we conducted a systematic review and meta-regression analysis of acute, crossover, single-meal feeding trials that examined the effects of adding OBG or oat bran to a carbohydrate-containing test-meal versus a control test-meal containing an equivalent amount of available-carbohydrate (avCHO) from the same or similar source. Medline, Embase, and Cochrane Library were searched up to 18 August 2021. The primary outcome was glucose incremental-area-under-the-curve (iAUC). Secondary outcomes included insulin iAUC, and glucose and insulin incremental peak-rise (iPeak). Two independent reviewers extracted data. Results were expressed as ratio-of-means (RoM) with 95% confidence intervals (CIs). Linear associations were assessed by random effects meta-regression. MinDose was defined as the dose at which the upper 95% CI of the regression line cut the line of no effect (i.e., RoM = 1). Fifty-nine comparisons (n = 340) were included; 57 in healthy subjects without diabetes and two in subjects with diabetes; 24 high-MW (>1000 kg/mol), 22 medium-MW (300–1,000 kg/mol), and 13 low-MW (<300 kg/mol). In healthy subjects without diabetes the associations between OBG dose and glucose iAUC and iPeak were linear (non-linear p value >0.05). MinDoses for glucose iAUC for high-MW, medium-MW and low-MW OBG, respectively, were estimated to be 0.2 g, 2.2 g and 3.2 g per 30 g avCHO; MinDoses for glucose iPeak were less than those for iAUC. Insufficient data were available to assess MinDose for insulin, however, there was no evidence of a disproportionate increase in insulin. More high-quality trials are needed to establish MinDose in individuals with diabetes.
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The consumption of dates with coffee is common among Arabs and may affect postprandial hyperglycemia ex-cursion. The study aimed to determine the effect of coffee on the glycemic index of a common variety of dates (Khalas) tested in healthy and type 2 diabetes mellitus individuals. Study subjects were thirteen healthy volunteers (mean age: 40.2±6.7 years) and ten diabetic participants with a mean HbA1c of 6.6±(0.7%) and a mean age of 40.8±5.7 years. Each subject participated in five days of tests with 50 g of glucose and 50 g equivalent of available carbohydrates from the dates (with/without coffee). Capillary glucose was measured in the healthy subjects at 0, 15, 30, 45, 60, 90 and 120 min, and for the diabetics at 0, 30, 60, 90, 120, 150 and 180 min. Glycemic indices were determined as ratios of the incremental areas under the response curves for the interventions. Statistical analyses were performed using the independent samples and paired t-tests. Mean±SE glycemic indices of the Khalas dates for the healthy individuals were 55.1±7.7 and 52.7±6.2 without and with coffee consumption, respectively. Similar values were observed for those with diabetes (53.0±6.0 and 41.5±5.4). Differences between glycemic indices of Khalas with or without coffee were not significant (p=0.124). There were no significant differences in glycemic index between the diabetic and healthy subjects (p=0.834 and p=0.202 without and with coffee respectively). In conclusion, at least in the short term, coffee does not adversely affect capillary glucose levels following Khalas dates consumption in healthy and diabetic volunteers.
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Glycaemic index (GI) testing provides a useful point of comparison between carbohydrate sources. For this comparison to be meaningful, the methods used to determine GI values need to be rigorous and consistent between testing events. This requirement has led to increasing standardization of the GI methodology, with an international standard developed in joint consultation with FAO/WHO (ISO 26642:2010) currently the most up to date document. The purpose of this review is to compare the international standard to methods of published studies claiming to have performed a GI test. This analysis revealed that the international standard permits a wide range of choices for researchers when designing a GI testing plan, rather than a single standardized protocol. It has also been revealed that the literature contains significant variation, both between studies and from the international standard for critical aspects of GI testing methodology. The primary areas of variation include; what glucose specification is used, which reference food is used, how much reference food is given, what drink is given during testing, the blood sampling site chosen and what assay and equipment is used to measure blood glucose concentration. For each of these aspects we have explored some of the methodological and physiological implications of these variations. These insights suggest that whilst the international standard has assisted with framing the general parameters of GI testing, further stan-dardization to testing procedures is still required to ensure the continued relevance of the GI to clinical nutrition.
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Polyphenols, including flavonoids, phenolic acids, proanthocyanidins and resveratrol, are a large and heterogeneous group of phytochemicals in plant-based foods, such as tea, coffee, wine, cocoa, cereal grains, soy, fruits and berries. Growing evidence indicates that various dietary polyphenols may influence carbohydrate metabolism at many levels. In animal models and a limited number of human studies carried out so far, polyphenols and foods or beverages rich in polyphenols have attenuated postprandial glycemic responses and fasting hyperglycemia, and improved acute insulin secretion and insulin sensitivity. The possible mechanisms include inhibition of carbohydrate digestion and glucose absorption in the intestine, stimulation of insulin secretion from the pancreatic beta-cells, modulation of glucose release from the liver, activation of insulin receptors and glucose uptake in the insulin-sensitive tissues, and modulation of intracellular signalling pathways and gene expression. The positive effects of polyphenols on glucose homeostasis observed in a large number of in vitro and animal models are supported by epidemiological evidence on polyphenol-rich diets. To confirm the implications of polyphenol consumption for prevention of insulin resistance, metabolic syndrome and eventually type 2 diabetes, human trials with well-defined diets, controlled study designs and clinically relevant end-points together with holistic approaches e.g., systems biology profiling technologies are needed.
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Epidemiological studies indicate an inverse association of coffee consumption with risk of type 2 diabetes mellitus. However, studies to determine the clinical effects of coffee consumption on the glucose metabolism biomarkers remain uncertain. The aim of this systematic review was to evaluate the effects of coffee consumption on glucose metabolism. A search of electronic databases (PubMed and Web of Science) was performed identifying studies published until September 2017. Eight clinical trials (n = 247 subjects) were identified for analyses. Participants and studies characteristics, main findings, and study quality (Jadad Score) were reported. Short-term (1–3 h) and long-term (2–16 weeks) studies were summarized separately. Short-term studies showed that consumption of caffeinated coffee may increase the area under the curve for glucose response, while for long-term studies, caffeinated coffee may improve the glycaemic metabolism by reducing the glucose curve and increasing the insulin response. The findings suggest that consumption of caffeinated coffee may lead to unfavourable acute effects; however, an improvement on glucose metabolism was found on long-term follow-up. © 2018 Center for Food and Biomolecules, National Taiwan University
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The glycaemic index (GI) concept was originally introduced to classify different sources of carbohydrate (CHO)-rich foods, usually having an energy content of >80 % from CHO, to their effect on post-meal glycaemia. It was assumed to apply to foods that primarily deliver available CHO, causing hyperglycaemia. Low-GI foods were classified as being digested and absorbed slowly and high-GI foods as being rapidly digested and absorbed, resulting in different glycaemic responses. Low-GI foods were found to induce benefits on certain risk factors for CVD and diabetes. Accordingly it has been proposed that GI classification of foods and drinks could be useful to help consumers make 'healthy food choices' within specific food groups. Classification of foods according to their impact on blood glucose responses requires a standardised way of measuring such responses. The present review discusses the most relevant methodological considerations and highlights specific recommendations regarding number of subjects, sex, subject status, inclusion and exclusion criteria, pre-test conditions, CHO test dose, blood sampling procedures, sampling times, test randomisation and calculation of glycaemic response area under the curve. All together, these technical recommendations will help to implement or reinforce measurement of GI in laboratories and help to ensure quality of results. Since there is current international interest in alternative ways of expressing glycaemic responses to foods, some of these methods are discussed.
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The phenomenon of accelerated gastric emptying has been previously reported in two conditions that are considered to be part of the insulin-resistance syndrome: namely, noninsulin-dependent diabetes (NIDDM) and increased body mass index (BMI). No previous studies have assessed the rate of gastric emptying in patients with essential hypertension, another disease considered to be part of the insulin-resistance syndrome. Scintigraphic gastric emptying studies were performed on nine hypertensive subjects and on nine sex-, age-, ethnicity and BMI-matched controls. Subjects with hypertension had significantly more rapid gastric half-emptying times (gastric T50) (40.0 +/- 6.9 min versus 56.6 +/- 3.7 min, p = 0.02) than controls. There was an inverse relationship between average glucose during the first 30 min and 60 min of the oral glucose tolerance test with the gastric half-emptying time (Spearman rank correlation coefficient rs = -0.64, p = 0.0045 and rs = -0.48, p = 0.0428, respectively). The occurrence of accelerated gastric emptying in hypertensive subjects, in addition to that previously reported in subjects with NIDDM or increased BMI, suggests the possibility that accelerated gastric emptying may be a common finding in insulin resistant states.
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The effects of volume and posture on gastric emptying and intragastric distribution of a solid meal and appetite were evaluated. Eight normal volunteers were studied on four occasions, on each of which a meal comprising ground beef mixed with tomato sauce of either 650 g ("large") or 217 g ("small") was eaten. Two studies were performed while the subject was lying in the left lateral decubitus position, and two studies were performed while the subject was sitting so that in each subject data were available for both meals and in both postures. Hunger and fullness were evaluated using a visual analog questionnaire. In both postures and after both meals, gastric emptying approximated a linear pattern after an initial lag phase. The lag phase was shorter for the large meal when compared with the small meal [sitting: large 13 +/- 5 vs. small 29 +/- 7 min; left lateral: large 16 +/- 3 vs. small 24 +/- 3 min, F(1, 7) = 46.3, P < 0.0005]. In both postures the contents of the total [F(1,7) = 1794.5, P < 0.0001], proximal [F(1,7) = 203.7, P < 0.0001], and distal [F(1,7) = 231.5, P < 0.0001] stomach were greater after the large meal when compared with the small meal. Although the 50% emptying time was greater with the large than the small meal [F(1,7) = 40.8, P < 0.001], the postlag emptying rate (g/min) was more rapid with the large meal [sitting: large 1.7 +/- 0.2 vs. small 1.1 +/- 0. 1 g/min; left lateral: large 1.8 +/- 0.1 vs. small 1.3 +/- 0.04 g/min, F(1,7) = 44.7, P < 0.0005]. There was a significant interaction between meal volume and posture for retention in the distal stomach [F(1,7) = 7.14, P < 0.05]. Contrasts were used to evaluate the effects of volume and posture between the four studies and demonstrated an effect of posture for the large [F(1,21) = 18.7, P < 0.005] but not the small [F(1,21) = 0.30, P = 0.60] meal so that the retention was greater in the sitting when compared with the left lateral position. The magnitude of the postprandial increase in fullness [F(1,7) = 7.8, P < 0.05] and reduction in hunger [F(1,7) = 5.9, P < 0.05] was greater with the large meal. We conclude that meal volume has a major effect on gastric emptying; in contrast posture has only a minor impact on intragastric meal distribution, which is observed only after a large meal, and no effect on gastric emptying.
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The purpose of this investigation was to examine the effect of caffeine (an adenosine receptor antagonist) on whole-body insulin-mediated glucose disposal in resting humans. We hypothesized that glucose disposal would be lower after the administration of caffeine compared with placebo. Healthy, lean, sedentary (n = 9) men underwent two trial sessions, one after caffeine administration (5 mg/kg body wt) and one after placebo administration (dextrose) in a double-blind randomized design. Glucose disposal was assessed using a hyperinsulinemic-euglycemic clamp. Before the clamp, there were no differences in circulating levels of methylxanthines, catecholamines, or glucose. Euglycemia was maintained throughout the clamp with no difference in plasma glucose concentrations between trials. The insulin concentrations were also similar in the caffeine and placebo trials. After caffeine administration, glucose disposal was 6.38 +/- 0.76 mg/kg body wt compared with 8.42 +/- 0.63 mg/kg body wt after the placebo trial. This represents a significant (P < 0.05) decrease (24%) in glucose disposal after caffeine ingestion. In addition, carbohydrate storage was 35% lower (P < 0.05) in the caffeine trial than in the placebo trial. Furthermore, even when the difference in glucose disposal was normalized between the trials, there was a 23% difference in the amount of carbohydrate stored after caffeine administration compared with placebo administration. Caffeine ingestion also resulted in higher plasma epinephrine levels than placebo ingestion (P < 0.05). These data support our hypothesis that caffeine ingestion decreases glucose disposal and suggests that adenosine plays a role in regulating glucose disposal in resting humans.
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The caffeine-induced impairment of insulin action is commonly attributed to adenosine receptor (AR) antagonism in skeletal muscle. However, epinephrine, a potent inhibitor of insulin actions, is increased after caffeine ingestion. We tested the hypothesis that the insulin antagonistic effects of caffeine are mediated by epinephrine, and not by AR antagonism, in seven healthy men. On four separate occasions, they received 1) dextrose (placebo, PL), 2) 5 mg/kg caffeine (CAF), 3) 80 mg of propranolol (PR), and 4) 5 mg/kg caffeine + 80 mg of propranolol (CAF + PR) before an oral glucose tolerance test (OGTT). Blood glucose was similar among trials before and during the OGTT. Plasma epinephrine was elevated (P < 0.05) in CAF and CAF + PR. Areas under the insulin and C-peptide curves were 42 and 39% greater (P < 0.05), respectively, in CAF than in PL, PR, and CAF + PR. In the presence of propranolol (CAF + PR), these responses were similar to PL and PR. These data suggest that the insulin antagonistic effects of caffeine in vivo are mediated by elevated epinephrine rather than by peripheral AR antagonism.
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Accumulating evidence suggests that certain dietary polyphenols have biological effects in the small intestine that alter the pattern of glucose uptake. Their effects, however, on glucose tolerance in humans are unknown. The objective was to investigate whether chlorogenic acids in coffee modulate glucose uptake and gastrointestinal hormone and insulin secretion in humans. In a 3-way, randomized, crossover study, 9 healthy fasted volunteers consumed 25 g glucose in either 400 mL water (control) or 400 mL caffeinated or decaffeinated coffee (equivalent to 2.5 mmol chlorogenic acid/L). Blood samples were taken frequently over the following 3 h. Glucose and insulin concentrations tended to be higher in the first 30 min after caffeinated coffee consumption than after consumption of decaffeinated coffee or the control (P < 0.05 for total and incremental area under the curve for glucose and insulin). Glucose-dependent insulinotropic polypeptide secretion decreased throughout the experimental period (P < 0.005), and glucagon-like peptide 1 secretion increased 0-120 min postprandially (P < 0.01) after decaffeinated coffee consumption compared with the control. Glucose and insulin profiles were consistent with the known metabolic effects of caffeine. However, the gastrointestinal hormone profiles were consistent with delayed intestinal glucose absorption. Differences in plasma glucose, insulin, and gastrointestinal hormone profiles further confirm the potent biological action of caffeine and suggest that chlorogenic acid might have an antagonistic effect on glucose transport. Therefore, a novel function of some dietary phenols in humans may be to attenuate intestinal glucose absorption rates and shift the site of glucose absorption to more distal parts of the intestine.
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Although acute alkaloid caffeine (CAF) ingestion results in an impaired glucose tolerance, chronic coffee (RCOF) ingestion decreases the risk of developing type 2 diabetes. This study examines the hypothesis that CAF ingestion impairs glucose tolerance to a greater extent than RCOF and that the ingestion of decaffeinated coffee (DECAF) results in a positive effect. Eleven healthy males underwent 4 double-blinded randomized trials. Each trial included the ingestion of either: 1) CAF in capsule form (4.45 mg/kg body weight), 2) RCOF (4.45 mg/kg body weight caffeine), 3) dextrose (placebo, PL) in capsule form, or 4) DECAF (equal in volume to the RCOF trial), followed 1-h later by a 2-h oral glucose tolerance test. Blood samples were collected at baseline (-30), 0 (time of treatment ingestion), 60 (initiation of oral glucose tolerance test), 75, 90, 120, 150, and 180 min. Area under the curve for glucose and insulin were higher (P < or = 0.05) following CAF than both PL and DECAF and, although a similar trend (P = 0.07) was observed following RCOF compared with DECAF, the effect was less pronounced. Interestingly, DECAF resulted in a 50% lower glucose response (P < or = 0.05) than PL, suggesting that the effects of PL and DECAF on glucose tolerance are not the same. These findings suggest that the effects of CAF and RCOF are not identical and may provide a partial explanation as to why acute CAF ingestion impairs glucose tolerance while chronic RCOF ingestion protects against type 2 diabetes.
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To determine the effects of black tea on postprandial plasma glucose and insulin concentrations in healthy humans in response to an oral glucose load. A four-way randomised, crossover trial was designed in which 16 healthy fasted subjects would consume 75g of glucose in either 250ml of water (control), 250ml of water plus 0.052g of caffeine (positive control) or 250 ml of water plus 1.0g or 3.0g of instant black tea. Blood samples were collected at fasting and at 30min intervals for 150min from commencement of drink ingestion. Glucose and insulin concentrations were measured using standard methodology. The tea was chemically characterised using colorimetric and HPLC methods. Chemical analysis showed that the tea was rich in polyphenolic compounds (total, 350mg/g). Results from only 3 treatment arms are reported because the 3.0g tea drink caused gastrointestinal symptoms. Plasma glucose concentrations <60min in response to the drinks were similar, but were significantly reduced at 120min (P<0.01), following ingestion of the 1.0g tea drink, relative to the control and caffeine drinks. Tea consumption resulted in elevated insulin concentrations compared with the control and caffeine drinks at 90min (P<0.01) and compared with caffeine drink alone at 150min (P<0.01). The 1.0g tea drink reduced the late phase plasma glucose response in healthy humans with a corresponding increase in insulin. This may indicate that the attenuation in postprandial glycemia was achieved as a result of an elevated insulin response following stimulation of pancreatic beta-cells. This effect may be attributable to the presence of phenolic compounds in the tea.
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Inconsistent findings from observational studies have prolonged the controversy over the effects of dietary glycemic index (GI) and glycemic load (GL) on the risk of certain chronic diseases. The objective was to evaluate the association between GI, GL, and chronic disease risk with the use of meta-analysis techniques. A systematic review of published reports identified a total of 37 prospective cohort studies of GI and GL and chronic disease risk. Studies were stratified further according to the validity of the tools used to assess dietary intake. Rate ratios (RRs) were estimated in a Cox proportional hazards model and combined by using a random-effects model. From 4 to 20 y of follow-up across studies, a total of 40 129 incident cases were identified. For the comparison between the highest and lowest quantiles of GI and GL, significant positive associations were found in fully adjusted models of validated studies for type 2 diabetes (GI RR = 1.40, 95% CI: 1.23, 1.59; GL RR = 1.27, 95% CI: 1.12, 1.45), coronary heart disease (GI RR = 1.25, 95% CI: 1.00, 1.56), gallbladder disease (GI RR = 1.26, 95% CI: 1.13, 1.40; GL RR = 1.41, 95% CI: 1.25, 1.60), breast cancer (GI RR = 1.08, 95% CI: 1.02, 1.16), and all diseases combined (GI RR = 1.14, 95% CI: 1.09, 1.19; GL RR = 1.09, 95% CI: 1.04, 1.15). Low-GI and/or low-GL diets are independently associated with a reduced risk of certain chronic diseases. In diabetes and heart disease, the protection is comparable with that seen for whole grain and high fiber intakes. The findings support the hypothesis that higher postprandial glycemia is a universal mechanism for disease progression.
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The glycaemic index (GI) is a measure of the ability of a food to raise blood sugar. Written by one of the co-inventors of the term, this is a clear and balanced review of current knowledge on this controversial concept. The book explores all the key issues of the definition of the GI, how to measure the GI of a food, how to apply GI information to meals and diets, the reasons why foods have different GI values and the impact of altering a diet GI on health and disease. The book highlights the benefits and the problems surrounding the GI concept, whilst encouraging readers to think critically about the issues involved.
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To study the effect of volume and type of beverage consumed with a meal on blood glucose (BG) responses, 12 normal subjects ate a standard test meal, Diabetes Screening Product (DSP), with 50, 250, 500, 750 or 1000ml water, or 250ml coffee or tea on separate days after overnight fasts. Water volumes were tested twice, making 12 tests done by each subject in a randomized block design. Finger-prick blood was taken before and 15, 30, 45, 60, 90 and 120min after starting to eat. The mean and variation of BG responses were compared by 2-way ANOVA. Mean BG 15min after DSP plus 500ml water was 0.6mmol/L greater than after DSP plus 50ml water (p<0.05). At 30min, BG was 0.5–0.7mmol/L greater after 500 and 750ml water than 50, 250, and 1000ml (p<0.005). At 90min, BG was 0.3mmol/L greater after 50 and 250ml water than after 500 and 750ml (p<0.005). At 120min, BG was 0.5mmol/L greater after 50ml than 500 and 750ml (p<0.001). Coffee and tea resulted in greater 45min BG than the same volume of water (p<0.005), while BG 60min after coffee was greater than after both tea and water (p<0.05). Volume and type of beverage did not significantly affect the incremental area under the curve or the variability of BG. We conclude that, in normal subjects, the volume and type of beverage consumed with a test meal influences the pattern of blood glucose response but has no effect on the incremental area under the glycaemic response curve. Since the volume, but not the type of beverage, affected the blood glucose concentration 2h after eating, a standardized meal volume should be used when testing an individual's carbohydrate tolerance status.
Article
Oral glucose tolerance tests were performed on 23 normal subjects and then repeated one week later. On one occasion, the test meal consisted of glucose dissolved in water and flavored with lemon juice; on the other occasion, 5 Gm. of instant coffee were also added to the meal. The order of administration of the respective meals was randomized. Serial blood samples were obtained and analyzed for blood glucose concentration, serum free fatty acid levels and the serum immunoreactive insulin values. Paired comparisons of the data were made and the following results were obtained: (1) The subjects ingesting coffee plus glucose had significantly lower blood glucose levels 30 and 60 minutes postprandium than those consuming the glucose solution without coffee. (2) Three hours after ingestion of the test meal, the free fatty acid levels of the subjects receiving coffee with glucose were significantly higher than those receiving glucose without coffee. (3) No statistically significant differences between the two groups were found at any time period for the serum immunoreactive insulin levels. It is possible that coffee ingestion reduced the peak postprandial blood glucose levels by mobilizing a hormone from the gastrointestinal tract such as secretin, pancreozymin, or the newly discovered substance with glucagon-like immunoreactivity described by Unger et al37.
Article
The gastric acid response to a 200-ml cup of tea was measured by in situ titration in 36 patients with duodenal ulcer (DU) and 56 without duodenal ulcer (controls). Tea resulted in an acid secretory response which was almost equal to that after a maximal dose (0.04 mg/kg) of histamine. The effect of tea was mainly due to its local chemical action on gastric mucosa. Tea without milk and sugar resulted in an acid response higher than that evoked by a maximal dose of histamine. The concentration of tea brew that had the greatest effect on gastric acid secretion was 15 g/200 ml, which was three times as much as that in a palatable cup of tea. Tea is a potent stimulant of gastric acid, and this can be reduced by adding milk and sugar.
Article
Intraindividual variation in the results of repeated oral glucose tolerance tests in normal subjects is well recognized but incompletely explained. The present studies show that such variation can be produced by ingestion of the glucose solution during different phases of the normal fasting activity cycle of the upper gut. Such variation is not seen when glucose is administered intraduodenally during the same phases of activity. Gastric emptying shows similar variation with the activity cycle; larger volumes of solution were emptied from the stomach during activity than quiescence, thus presenting greater quantities of glucose solution to the small intestine for absorption. Metoclopramide and hyoscine butylbromide, drugs known to influence the rate of gastric emptying, reduced the variation in the glucose tolerance test. The data suggest na possible use of the glucose tolerance test for the assessment of gastric emptying.
Article
The relationships between gastric emptying and intragastric distribution of glucose and oral glucose tolerance were evaluated in 16 healthy volunteers. While sitting in front of a gamma camera the subjects drank 350 ml water containing 75 g glucose and 20 MBq 99mTc-sulphur colloid. Venous blood samples for measurement of plasma glucose, insulin and gastric inhibitory polypeptide were obtained at--2, 2,5,10,15,30,45,60,75,90,105,120 and 150 min. Gastric emptying approximated a linear pattern after a short lag phase (3.3 +/- 0.8 min). The 50% emptying time was inversely related to the proximal stomach 50% emptying time (r = -0.55, p < 0.05) and directly related to the retention in the distal stomach at 120 min (r = 0.72, p < 0.01). Peak plasma glucose was related to the amount emptied at 5 min (r = 0.58, p < 0.05) and the area under the blood glucose curve between 0 and 30 min was related to the amount emptied at 30 min (r = 0.58, p < 0.05). In contrast, plasma glucose at 120 min was inversely related to gastric emptying (r = -0.56, p < 0.05) and plasma insulin at 30 min (r = -0.53, p < 0.05). Plasma insulin at 120 min was inversely related (r = -0.65, p < 0.01) to gastric emptying. The increase in plasma gastric inhibitory polypeptide at 5 min was related directly to gastric emptying (r = 0.53, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The effect of coffee on gastric emptying was addressed in a scintigraphic liquid-phase gastric emptying study in patients with non-ulcer dyspepsia. Ninety-three subjects (56 males, 37 females; mean age 40 years, range 17-77 years) diagnosed as having non-ulcer dyspepsia were enrolled in the study. The baseline study was to drink 500 ml of 5% glucose water and the coffee study was to drink 500 ml of 5% glucose water containing 4 g of regular instant coffee. The two studies were performed on separate days. Fifteen of the 93 subjects were chosen at random to undergo repeated coffee studies for evaluation of reproducibility. Overall the 93 subjects showed accelerated gastric emptying, as measured by half emptying time (T1/2) with coffee compared with baseline (35.7 +/- 10.5 vs 45.0 +/- 23.1 min, P < 0.001). However, 68 (73.2%) subjects showed accelerated emptying (-14.8 +/- 19.5 min), while 25 (26.8%) subjects showed delayed emptying (5.9 +/- 4.5 min) after ingestion of coffee. There was no significant difference in the change in gastric emptying with coffee in duplicate measurements from the 15 subjects who had two coffee studies (P = 0.082). We conclude that coffee accelerates liquid-phase gastric emptying in the majority of patients with non-ulcer dyspepsia.
Article
To determine the effect of variety and cooking method on glycemic response and glycemic index of common North American potatoes. Study 1: subjects consumed 200 g Russet or white potatoes that were either (a) precooked, refrigerated, and reheated (precooked) or (b) cooked and consumed immediately (day-cooked). Incremental area under the curve was determined. Study 2: subjects consumed 50 g carbohydrate portions of white bread or potatoes (six different varieties and two different cooking methods). Glycemic index values were calculated. In both studies meals were consumed after a 10- to 12-hour overnight fast and finger-prick capillary-blood glucose was measured before and at intervals for 2 hours after consumption. The study groups were as follows: Study 1 comprised four men and six women, aged 20 to 44 and Study 2 comprised 11 men and one woman, aged 18 to 50. Repeated measures analysis of variance with Newman-Kuels to protect for multiple comparisons (criterion of significance two-tailed P <.05). Study 1: Precooked Russet potatoes elicited lower area under the curve than day-cooked (P <.05), while precooking had no effect on boiled white potatoes. Study 2: The glycemic index values of potatoes varied significantly, depending on the variety and cooking method used (P =.003) ranging from intermediate (boiled red potatoes consumed cold: 56) to moderately high (roasted California white potatoes: 72; baked US Russet potatoes: 77) to high (instant mashed potatoes: 88; boiled red potatoes: 89). The glycemic index of potatoes is influenced by variety and method of cooking and US Russet potatoes have only a moderately high glycemic index. Individuals who wish to minimize dietary glycemic index can be advised to precook potatoes and consume them cold or reheated.
The glycemic index in the management of obesity
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Wolever TMS (2008) The glycemic index in the management of obesity. Endocrinology Rounds, vol. 8, issue 2. http://www. endocrinologyrounds.ca/crus/endo_02_08_eng.pdf
Glycaemic index methodology
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