With the rapid development of society and economy, children's simple obesity is the rising in the world and has become a chronic disease which is one of the biggest public health challenges in the world. It is a serious threat to the health of children and their adulthood. The overweight and obesity is induced by the genetic and environmental factors. The environmental factors are very important, while the dietary factors are the driving factors of many chronic diseases including obesity. This study focus on the dietary intervention of childhood obesity to build healthy intestinal flora. The interventing food was based on a natural health food - fruit and vegetable fermentation liquid, and combined with other probiotic dietary factors, dietary fiber and oligosaccharides. The implementation of the study will help to reveal the fuction mechanism of intestinal bacteria in the obese children and normal children, and to construct healthy micro environment of intestinal flor. According to the positive effect factors, the study will propose a healthy diet and nutrition intervention model for obese children, which is significant to social health especially to children's health.

To investigate the accuracy of MRI in quantifying liver fat with magnetic resonance spectroscopy (MRS) as a reference. A secondary goal was to assess the prevalence of nonalcoholic fatty liver disease in overweight and obese Chinese children and adolescents.

Before academic examination, letter to parents, informed consent and volunteer questionnaire are released to school children and their guardians. We tell the volunteers and their guardians what about this study and invite them to participate this study. Only the volunteers and guardians signature on the letter to parents and informed consent are able to the research objects.

Experimental procedures:

Two times of medical exams, blood and stool sample collection is required for the whole experiment research. The first time exams and sample collection is carried on during academic examination; the second time is carried on after the intervention.

Recruit of research objects:

According to academic examination and volunteer questionnaires, about 300 healthy children without in taking antibiotics before 3 months are recruited and their BMI should be in the obese range. Then their waist circumference and the ratio of body fat are measured. If the ratio of waist size to weight of them is >0.46 and they have higher percentage of body fat (>20% for boys and under 12 years old girls, >25% for 12 years old girls), the data are collected and input to the database. About 40 healthy children between 15-18 years old are recruited to participate the next intervention research.

General body examination:

In academic examination, the student's basic medical data including height and weight are recorded, and then their BMI are calculated. If his/her BMI are in the obese range, his/her body composition are measured and recorded.

MRI and MRS test:

All patients underwent MRI scanning performed by an experienced technologist using a 3 Tesla MR unit (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany). MRI and MRS were performed with multi-echo Dixon and HISTO sequences, respectively, to calculate hepatic proton density fat fraction (PDFF).

Blood collection, preservation and test:

Blood collection and preservation are proceed in standard of medical examination. When collecting the data of obesity, the tests of blood count, blood glucose, serum lipid and liver function should be processed for obese children. When intervening, more tests including blood count, blood glucose, blood lipids, liver function, hemoglobin, cytokines, insulin, high sensitivity C-reactive protein, leptin and somatomedin C should be processed.

Stool collection, preservation and detection:

50 ml centrifuge tubes are used to collect stool samples. Each tube is marked a unique encoding corresponds to a volunteer. When volunteers collecting stool samples, they transfer the stool samples into sterile centrifuge tube using sterile swabs or toothpicks as soon as possible. The collecting samples should be more than 10g. The centrifuge tubes should be put in low-temperature place , then transfer to refrigerator and stored at -80 ℃ until to DNA extraction and other testing. The tests including short chain fatty acids content (SCFA), pH, water content, immune factors sIgA and Calprotectin are processed.

16S rRNA gene sequencing of bacteria in stools:

DNA extraction:

For each sample, about 0.2g stool is weighted and the total DNA is extracted using fecal genomic DNA extraction Kit (Qiagen, model DP328). And then the concentration and purity of extracted DNA were measured using NanoDrop (Thermo, 2000C) to guarantee each sample meets the sequencing requirement.

Sample sequencing:

PCR amplification of 16S rRNA gene (V3-V4) are performed with universal forward primers 5'-ACTCCTACGGGAGGCAGCAG-3' and reverse primer 5'-GGACTACVSGGGTATCTAAT-3'. The amplification system include sterile water 19.375 ul, buffer 2.5ul, template 1ul, primers 1ul, Pyrobest DNA polymerase 0.125ul. PCR cycling conditions were as follows: 94 ℃ 5min, followed by some cycles including 94℃ denaturing for 30s, 50℃ renaturing for 30s,72℃ extending for 30s, then 72℃ extending for 5min. PCR product electrophoresis are performed to determine the appropriate PCR product with different application cycles. After connecting amplified products to tagged primers and labels, paired-end sequencing are performed with the sequencing platform of Illumina MiSeq, and the read length is about 250bp.

Intervention treatment on childhood obesity with PFE:

After 16S rRNA gene sequencing, about 40 obese volunteers in high school and with similar intestinal flora profiles are selected to participate the intervention treatment research. The intervening food is "Dr. Ephraim" plant fermentation extract (PFE). Without changing the previous diets of research objects, each research object drinks drinking 30mL PFE at morning and evening enzymes respectively, and the intervention last for 8 weeks. Before and after 8-week intervention, stool and blood samples of research objects are collected and analyzed to obtain their physiological and biochemical indexes. The all 16S rRNA gene of fecal samples in each stage are sequenced.

Inclusion Criteria:

• People whose BMI>27 and Age between 15-18;the value of waistline/weight >0.46; the value of body composition >20%.

Exclusion Criteria:

• People treated by antibiotic drugs in 3 months;People with gastrointestinal diseases;People with Type I diabetes, any eating disorders such as bulimia or anorexia nervosa; Prader-Willi patients and obesity is part of clinical syndrome with other disorders.