In this study, the investigators are interested in investigating how the emulsification state and amount of fat in a meal can modify the kinetics of postprandial lipemia and inflammatory outcomes (including endotoxemia) in obese vs lean subjects.

10 lean and 10 obese volunteers will come 3 times (>3 weeks apart) at the investigation center to receive a standard breakfast containing milk fat (10 g non emulsified, or 40 g non emulsified, or 40 g finely emulsified). 13C triglyceride stable isotopes will allow to follow the metabolic fate of fatty acids and calculate lipid oxidation by breath test. Blood sampling throughout digestion will allow to measure metabolic, lipid and inflammation parameters. Stool will be analysed to determine lipid losses in faeces and to phenotype microbiota.

Inclusion Criteria:

• No smokers
• BMI 18 to 35 kg/m2
• Moderate physical activity
• Safety subject during medical consultation

Exclusion Criteria:

• Medical history which may affect lipid metabolism and gut microflora (renal -cardiovascular -hepatic- endocrine-inflammatory diseases)
• Drug use that could affect lipid metabolism and gut microflora (steroids, antilipemic agent, anorectic, antibiotic)
• Inflammatory or infectious disease in the last three month
• C Reactive Protein > 20
• Prebiotic or probiotic high consumers (several times a day)
• Eating disorder
• Claustrophobic subjects