Elsevier

Nutrition Research

Volume 57, September 2018, Pages 67-77
Nutrition Research

Oil tea improves glucose and lipid levels and alters gut microbiota in type 2 diabetic mice

https://doi.org/10.1016/j.nutres.2018.05.004Get rights and content

Abstract

Oil tea has traditionally been used in minority populations in China for treating various ailments in traditional Chinese medicine. Individually, green tea and ginger, which are the main ingredients of oil tea, have demonstrated antidiabetic effects; however, whether oil tea exerts antidiabetic effects remains unknown. In addition, aberrant gut microbiota structure is associated with diabetic status, and research indicates that there may be beneficial effects of tea on gut microbiota. Therefore, we hypothesized that oil tea exerts antidiabetic effects and induces alteration in gut microbiota. To test our hypothesis, we first examined the nutrition composition of oil tea. Then, db/db mice were randomly divided into 3 groups and orally gavaged with saline, metformin, and oil tea for 8 weeks. Fasting blood glucose (FBG), oral glucose tolerance test (OGTT), and lipid levels were tested during the experiment. 16S rRNA genes were sequenced and changes in gut microbiota in response pre/post treatment were examined. Our experiments showed that oil tea contains high concentrations of tea polyphenols (246.35 mg/100 g) and [6]-gingerol (2.98 mg/100 g). It appeared that oil tea treatment significantly suppressed the postprandial blood glucose elevation and lowered the levels of FBG, total cholesterol, triglycerides, and LDL-cholesterol (P < .05). The composition of gut microbiota changed significantly in response to oil tea treatment, Lachnospiraceae were significantly enriched (q < 0.05, LDA score> 3.5). Redundancy analysis identified 155 oil tea-modulating family level phylotypes, where Lachnospiraceae significantly correlated with FBG, total cholesterol, and LDL-cholesterol (P < .05). Our findings demonstrate that oil tea improved glucose and lipid levels and modulated gut microbiota in db/db mice.

Introduction

Diabetes mellitus is a major public health problem in China, with a diabetes prevalence of 10.9% reported in the 2013 nationwide survey [1]. Prevention and treatment of diabetes thus represents a major challenge of modern society in China. Efforts to find “natural” or alternative medicines have increased markedly over the last several years, although the clinical efficacy of these are either mixed or wholly absent. In the province-wide nutrition survey conducted in Guangxi Province, China from 2013–2014, a 1.4% (9/647) prevalence of diabetes was found in an area which has a high oil tea consumption, Gongcheng Yao Autonomous County. This prevalence was much lower than the average frequency of diabetes in Guangxi [2] and in China [1]. This area has a cultural preference for frequent consumption of oil tea, used as both a common beverage and a base for multiple meals during the day, in addition to using it for the treatment and prevention of multiple aliments [3]. Green tea and ginger, as the main ingredients of oil tea and traditional herbal medicine [4], have each been demonstrated to exert antidiabetic effects, including in animal experiments [5], [6], [7], [8], cohort studies [9], [10], and randomized controlled trials [11], [12]. Oil tea, as a complex mixture of green tea, ginger, and oil, may therefore have antidiabetic effects.

Recent studies have shown that the beneficial effects of tea may be associated with gut microbiota [13], [14], [15]. Research shows that aberrant gut microbiota structure is associated with various metabolic disorders, including diabetes, obesity, and metabolic syndrome [16], [17]. It is also well recognized that gut microbiota responds to fluctuations in dietary composition [18] and reciprocally, changes in the microbiome have profound effects on the host. Potentially, by positively modulating the gut microbiota, results may have a beneficial impact on overall health, including diabetes-related outcomes.

In the present study, we investigated the effects of oil tea on type 2 diabetes and its subsequent effect on the composition of gut microbiota. The oil tea was prepared as usually consumed. We hypothesized that oil tea exerts antidiabetic effects and induces alterations in gut microbiota. To investigate this hypothesis, a genetic model of type 2 diabetes, db/db mice was used for oil tea treatment. Levels of fasting and postprandial blood glucose and serum lipid were measured, 16S rRNA genes were sequenced, and the response of gut microbiota to oil tea treatment was examined.

Section snippets

Preparation of oil tea

Oil tea was prepared using a modification of the local manufacturing method of Gongcheng Yao Autonomous County, Guangxi Province, China [19]. Briefly, oil tea contains green tea, ginger, peanut, cooking oil, and salt with the proportion of 9:10:5:2:1. The manufacturing process is as follows. First, soaked green tea leaf was stir-fried and beaten with ginger, peanut, and cooking oil in a hot iron pot for three minutes; second, hot water and salt were added; and third, the mixture was boiled for

Main nutrition composition of oil tea

As shown in Table 2, oil tea contains very high concentrations of tea polyphenols (2463.5 mg/kg) and caffeine (377 mg/kg). Appreciable concentrations of [6]-gingerol (29.8 mg/kg) and manganese (5 mg/kg) were also detected. Meanwhile, less than 1% of the NRV of proteins and carbohydrates were detected, and oil tea had low energy content (33.19KJ/100 g).

Effect of oil tea on FBG

As shown in Fig. 1, lower FBG levels were observed in both the oil tea and MET treatment groups during the 8-week experiment, and a significant

Discussion

In this study, we found for the first time that oil tea, a traditional tea beverage consumed in the minority areas of Guangxi, China, has antidiabetic effects, such as lowering FBG levels and improving glucose tolerance. Oil tea treatment also resulted in significantly reduced TC, LDL, and TG levels and significantly modulated the composition of gut microbiota.

The medicinal properties of green tea and ginger have long been recognized in China, since having been recorded in the “Compendium of

Acknowledgment

This work was supported by the National Natural Science Foundation of China (No.81660540), Guangxi Natural Science Foundation (Grant No. 2015GXNSFCA139010), and Technology Foundation for Selected Overseas Chinese Scholar, Ministry of Personnel of China (No. [2016] 176). The authors declare that they have no conflicts of interest.

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