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      Does green tea affect postprandial glucose, insulin and satiety in healthy subjects: a randomized controlled trial

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          Abstract

          Background

          Results of epidemiological studies have suggested that consumption of green tea could lower the risk of type 2 diabetes. Intervention studies show that green tea may decrease blood glucose levels, and also increase satiety. This study was conducted to examine the postprandial effects of green tea on glucose levels, glycemic index, insulin levels and satiety in healthy individuals after the consumption of a meal including green tea.

          Methods

          The study was conducted on 14 healthy volunteers, with a crossover design. Participants were randomized to either 300 ml of green tea or water. This was consumed together with a breakfast consisting of white bread and sliced turkey. Blood samples were drawn at 0, 15, 30, 45, 60, 90, and 120 minutes. Participants completed several different satiety score scales at the same times.

          Results

          Plasma glucose levels were higher 120 min after ingestion of the meal with green tea than after the ingestion of the meal with water. No significant differences were found in serum insulin levels, or the area under the curve for glucose or insulin. Subjects reported significantly higher satiety, having a less strong desire to eat their favorite food and finding it less pleasant to eat another mouthful of the same food after drinking green tea compared to water.

          Conclusions

          Green tea showed no glucose or insulin-lowering effect. However, increased satiety and fullness were reported by the participants after the consumption of green tea.

          Trial registration number

          NCT01086189

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          Most cited references19

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          Tea catechins and polyphenols: health effects, metabolism, and antioxidant functions.

          Increasing interest in the health benefits of tea has led to the inclusion of tea extracts in dietary supplements and functional foods. However, epidemiologic evidence regarding the effects of tea consumption on cancer and cardiovascular disease risk is conflicting. While tea contains a number of bioactive chemicals, it is particularly rich in catechins, of which epigallocatechin gallate (EGCG) is the most abundant. Catechins and their derivatives are thought to contribute to the beneficial effects ascribed to tea. Tea catechins and polyphenols are effective scavengers of reactive oxygen species in vitro and may also function indirectly as antioxidants through their effects on transcription factors and enzyme activities. The fact that catechins are rapidly and extensively metabolized emphasizes the importance of demonstrating their antioxidant activity in vivo. In humans, modest transient increases in plasma antioxidant capacity have been demonstrated following the consumption of tea and green tea catechins. The effects of tea and green tea catechins on biomarkers of oxidative stress, especially oxidative DNA damage, appear very promising in animal models, but data on biomarkers of in vivo oxidative stress in humans are limited. Larger human studies examining the effects of tea and tea catechin intake on biomarkers of oxidative damage to lipids, proteins, and DNA are needed.
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            Low-glycemic index diets in the management of diabetes: a meta-analysis of randomized controlled trials.

            The use of diets with low glycemic index (GI) in the management of diabetes is controversial, with contrasting recommendations around the world. We performed a meta-analysis of randomized controlled trials to determine whether low-GI diets, compared with conventional or high-GI diets, improved overall glycemic control in individuals with diabetes, as assessed by reduced HbA(1c) or fructosamine levels. Literature searches identified 14 studies, comprising 356 subjects, that met strict inclusion criteria. All were randomized crossover or parallel experimental design of 12 days' to 12 months' duration (mean 10 weeks) with modification of at least two meals per day. Only 10 studies documented differences in postprandial glycemia on the two types of diet. Low-GI diets reduced HbA(1c) by 0.43% points (CI 0.72-0.13) over and above that produced by high-GI diets. Taking both HbA(1c) and fructosamine data together and adjusting for baseline differences, glycated proteins were reduced 7.4% (8.8-6.0) more on the low-GI diet than on the high-GI diet. This result was stable and changed little if the data were unadjusted for baseline levels or excluded studies of short duration. Systematically taking out each study from the meta-analysis did not change the CIs. Choosing low-GI foods in place of conventional or high-GI foods has a small but clinically useful effect on medium-term glycemic control in patients with diabetes. The incremental benefit is similar to that offered by pharmacological agents that also target postprandial hyperglycemia.
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              Epigallocatechin gallate, a constituent of green tea, represses hepatic glucose production.

              Herbs have been used for medicinal purposes, including the treatment of diabetes, for centuries. Plants containing flavonoids are used to treat diabetes in Indian medicine and the green tea flavonoid, epigallocatechin gallate (EGCG), is reported to have glucose-lowering effects in animals. We show here that the regulation of hepatic glucose production is decreased by EGCG. Furthermore, like insulin, EGCG increases tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 (IRS-1), and it reduces phosphoenolpyruvate carboxykinase gene expression in a phosphoinositide 3-kinase-dependent manner. EGCG also mimics insulin by increasing phosphoinositide 3-kinase, mitogen-activated protein kinase, and p70(s6k) activity. EGCG differs from insulin, however, in that it affects several insulin-activated kinases with slower kinetics. Furthermore, EGCG regulates genes that encode gluconeogenic enzymes and protein-tyrosine phosphorylation by modulating the redox state of the cell. These results demonstrate that changes in the redox state may have beneficial effects for the treatment of diabetes and suggest a potential role for EGCG, or derivatives, as an antidiabetic agent.
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                Author and article information

                Journal
                Nutr J
                Nutrition Journal
                BioMed Central
                1475-2891
                2010
                30 November 2010
                : 9
                : 63
                Affiliations
                [1 ]Lund University, Skåne University Hospital, Lund University, Malmö, Sweden
                [2 ]Center for Emergency (JW, JH), Lund University, Skåne University Hospital, Lund University, Malmö, Sweden
                [3 ]Department of Cardiothoracic Surgery, Lund University, Skåne University Hospital, Lund University, Lund, Sweden
                Article
                1475-2891-9-63
                10.1186/1475-2891-9-63
                3002911
                21118565
                02313419-72eb-4c1b-93bc-501ef34c03a3
                Copyright ©2010 Josic et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 1 August 2010
                : 30 November 2010
                Categories
                Research

                Nutrition & Dietetics
                Nutrition & Dietetics

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