The main objective of this study is to investigate in detail how a high-(prebiotic)fibre diet and a high-PUFA diet affect the gut microbiota composition in a metabolic challenged population, and if the diet-induced modulation of the gut microbiota mediates changes in metabolic risk markers.

Intake of both experimental diets over 4 weeks are expected to induce beneficial changes in the gut microbiota composition and to affect markers for insulin sensitivity, lipid metabolism and inflammation. The investigators hypothesize that the effect of both interventions on the metabolic risk markers will be partly mediated by the diet-induced changes in the gut microbiota composition.

Inclusion Criteria:

• BMI: 25-40 kg/m2
• Non-smoking
• Indices of the Metabolic Syndrome defined by the International Diabetes Federation (IDF 2006):

Central obesity (waist circumference; men: ≥94 cm and women: ≥80 cm) + any one of the following; raised triglyceride level (≥1.7 mmol/L), reduced HDL cholesterol (men: <1.03 mmol/L, women: <1.29 mmol/L), raised BP (systolic ≥130 mm Hg or diastolic ≥85 mm Hg) or raised fasting plasma glucose (≥5.6 mmol/L).

Exclusion Criteria:

• Use of antibiotics
• Weight change >3 kg 2 months prior to study start
• Intensive physical training/ elite athlete
• Medication for dyslipidemia, type 2 diabetes or elevated blood pressure
• Dietary supplements with pro/prebiotics, dietary fibre or fish oil supplement
• Lactation, pregnancy or planning of pregnancy during the study
• Gastro intestinal and liver disorders
• Chronic inflammatory disorders
• Diagnosed psychiatric disorder including treatment required depression
• Surgical treatment of obesity and abdominal surgery