The study investigators hypothesize (1) that the SCFA/acetate metabolism differs between metabolic phenotypes and (2) that using a mixture of fibres that differ in degree of polymerization and branching namely a resistant starch and a human-like milk oligosaccharide enhance the acetate availability in the distal colon and systemic circulation, consequently leading to its metabolic effects.

To study this, the investigators will supplement lean, normoglycaemic vs. overweight/obese, prediabetic men with the fibre mixture the day before the clinical investigation day (CID) and study during the CID its effects on fasting and postprandial substrate and energy metabolism.

Inclusion criteria:

Lean (BMI ≥ 20kg/m2 and ≤ 24.9kg/m2) healthy men aged 30 - 65 years

as well as

overweight/obese (BMI ≥ 25kg/m2 and ≤ 34.9kg/m2) prediabetic men aged between 30 - 65 years

Exclusion criteria:

• Type 2 diabetes mellitus (defined as fasting plasma glucose ≥ 7.1 mmol/L and 2h glucose ≥ 11.1 mmol/L)
• Gastroenterological diseases or abdominal surgery;
• Cardiovascular diseases, cancer, liver or kidney malfunction, disease with a life expectancy shorter than 5 years;
• Abuse of products; alcohol and drugs, excessive nicotine use defined as >20 cigarettes per day;
• Plans to lose weight or following of a hypocaloric diet;
• Regular supplementation of pre- or probiotic products, use of pre- or probiotics 3 months prior to the start of the study;
• Intensive exercise training more than three hours a week;
• Use of any medication that influences glucose or fat metabolism and inflammation (i.e. NSAIDs);
• Regular use of laxation products;
• Use of antibiotics in the last three months (antibiotics use can alter substantially the gut microbiota composition).
• Follow a vegan diet.