The objective of this study is to investigate whether intake of a diet with a high content of butyrate (from dairy fat) can affect blood FIAF concentration compared to a control diet. Further to examine whether high intake of inulin (a prebiotic) can increase the proportion of butyrate-producing bacteria in the gut and thereby affect blood FIAF concentration. In addition, the correlation between FIAF blood concentrations and resting energy expenditure, blood lipid profile and gut microbiota composition will be investigated.

Furthermore, this study will investigate whether the source of FIAF can be determined. To this end, adipose tissue biopsies will be analyzed and an in vitro experiment with fecal water samples will be carried out.

The study is a crossover randomized controlled trials with 3 arms. Each arm has a duration of 3 weeks. 20 overweight/obese subjects will be enrolled into the study and randomized to the order of interventions. Before and after each intervention period, blood samples will be collected and the participants will have their resting metabolic rate measured. At the end of each intervention period, the participants will collect feces for 5 consecutive days. In addition, adipose tissue biopsies will be taken after each intervention period.

Inclusion Criteria:

• Healthy males
• Age: 23-45
• BMI: 25-32 kg/m2
• Body fat percentage (BFP) > 25

Exclusion Criteria:

• Chronic diseases (known diabetes, cardiovascular disease (CVD), Intestinal Bowel Disease and other chronic diseases likely to affect the results of the present study)
• Milk allergy/lactose intolerance
• Intolerance towards inulin
• Fasting glucose ≥7.0 mmol/l or non-fasting glucose ≥ 11 mmol/l*
• Use of antibiotics 2 months before commencement of study
• Use of dietary supplements incl. multivitamins during run-in and the entire study period
• Smoking
• Elite athletes (>10 hours of strenuous physical activity per week)
• Use of prescription medicine which could affect the results of the present study, including systemic glucocorticoids
• Use of lipid-lowering agents or medication with contraindications for a high fat diet
• Blood pressure > 140/90 mmHg
• Blood donation <1 month before study commencement and during study period
• Simultaneous participation in other clinical studies
• Inability, physically or mentally, to comply with the procedures required by the study protocol, as evaluated by the study staff