The aim of the present study is to find out if a dietary intervention mainly focusing on fructose reduction has a preventive effect on the development and progression of NAFLD and the metabolic syndrome in overweight children.

In the intervention study a total of 100 overweight and 50 normal weight children, aged 5-8 years have to be included. At the beginning, two 24-h dietary recalls are performed to assess nutritional intake and fructose consumption. Anthropometric parameters (body weight and height) are measured to calculate BMI and BMI-SDS of the children. Physical activity during leisure time as well as socio-demographic status and "family background" are assessed using different questionnaires. An ultrasound examination of the liver is performed in all participants for detection of signs of fatty liver. From each child included in the study a fasting blood sample is taken to determine the following blood parameters: ALT, AST, γ-GT, uric acid, blood lipids (TG, HDL, LDL, Total cholesterol), blood alcohol, PAI-1 and endotoxin concentration. A part of the blood sample is used for DNA-analysis. In all children systolic (SBP) and diastolic (DBP) blood pressure are also measured. An oral glucose tolerance test (OGTT) is performed after an overnight fast of 12 h (glucose concentration: 1.75 g/kg body weight, maximum 75g). Simultaneously a glucose hydrogen breath test is performed to assess small intestinal bacterial overgrowth (SIBO). After the check-ups at the beginning of the study, children are divided into two study groups: the intervention group and the control group. Based on the daily fructose intake assessed at the beginning of the study, children participating in the intervention group are advised to reduce their daily fructose intake by 50%. In the first study year, every three months and in the second study year, every six months, nutritional counseling is repeated in small groups in which parents and children are separately trained. If families participating in the control group wish, they receive a dietary counseling based on the references of the "DGE" at the beginning of the study. After the first and the second study year the examinations are repeated in all participants (ultrasound examination only after the second study year).

Inclusion Criteria:

• BMI > 90 percentile for overweight children
• BMI < 90 percentile for normal weight children
• no signs of fatty liver (maximal fatty liver grade one or slightly elevated ALT, AST, γ-GT concentrations)
• children with metabolic disorders (prehypertension, high triglyceride, cholesterol or fasting glucose levels) are included with agreement of the pediatrics

Exclusion Criteria:

• liver disease (e.g. steatohepatitis)
• diabetes type 1 and 2
• renal insufficiency
• chronic disease of the gastrointestinal tract
• taking drugs affecting lipid or glucose metabolism