Sugar alcohols such as xylitol and erythritol are increasingly popular as sugar substitutes in the food industry and are also recommended to diabetic patients. Both substances are already in use in the food industry and are freely available. Since the 1970s, beneficial effects on oral health could be demonstrated as oral bacteria were influenced positively. Animal studies showed an increase in gut Clostridium perfringens after xylitol intake; certainly a non-desirable effect. However, studies on effects of erythritol and xylitol on the human gut microbiota are lacking so far. In this trial, investigators aim to examine whether gut microbiota and glucose tolerance can be influenced by polyol intake in a non-diabetic but obese cohort.

Inclusion Criteria:

• Obese volunteers (BMI > 30kg/m2)
• Aged 18- max. 55 years
• Otherwise healthy.

Exclusion Criteria:

• Known cardiovascular disease
• Diabetes mellitus
• Arterial Hypertension with medication
• Dyslipidaemia with medication
• Known chronic hepatic disease (NASH, hepatitis).
• Known renal disease: kidney failure
• Pregnancy
• Intake of proton pump inhibitors (PPIs) on a regular basis
• Intake of antibiotics within the last 3 months before inclusion
• Intake of pro or prebiotics
• Chronical diseases of the gastrointestinal tract, history of gastrointestinal surgery with major changes to the gastrointestinal tract
• Substance abuse, alcohol abuse.
• Inability to follow procedures due to psychological disorders, dementia or insufficient knowledge of project language (German).