The investigators' project has as for principal objective to understand the impact of trans fatty acids from dairy products and industrial origin on the development of insulin resistance in obese woman. Because of the different isomeric position of the double bound those trans fatty acids may have different metabolic effects.

Women will be included in the study according to their susceptibility to develop a insulin resistance (evaluated starting from the body index of mass IMC superior to 28 kg.m-², of the waist measurement 88 cm). Once included in the study, the volunteers will receive for 4 weeks butter, dairy products and biscuits enriched in stearic, elaidic or vaccenic acid. The volunteers will undergo a measurement of the body composition by biphotonic absorptiometry as well as a complete metabolic assessment (blood and urinary samples, clamp to insulin and biopsies).

Inclusion Criteria:

• female
• waist measurement > 88 cm
• body mass index> 28kg/m2
• Affiliated to National Health Insurance
• Subject giving his/her written informed consent
• Subject willing to comply with the study procedures
• Subject considered as normal after clinical examination and medical questionnaire

Exclusion Criteria:

• Reported food allergies
• Currently participating or having participated in another clinical trial during the last 4 weeks prior to the beginning of this study
• Hepatic or renal impairments
• Positive serologies to HIV or HCV, determined on blood sample
• pregnant or presently attempting to get pregnant or menopause or lactating Blood donation done less than 2 months before the start of the study
• Chronic pathologies: diabetes, hypertriglyceridemia, hypertension, cardiovascular diseases, chronic inflammatory diseases
• Intestine, cardiovascular, kidney and cancer pathologies in the last 5 years
• Previous heavy intestine surgery (except appendicectomy)
• Previous medical and/or surgery judged by the investigator as incompatible with this study
• High variation (> 5%) of body weight during the last 3 months
• Consuming nutritional supplements which could interfered with lipid metabolism (fish oil capsule, vitamins, soja lecithins,…)
• Heavy consumer of alcohol
• Smoker or ex-smoker who stopped smoking less than 1 month before V0 (more than 5 cigarettes/dy).
• Practising intensive physical exercise (> 5 h per week)
• Vegetarian or vegan
• Being under someone's supervision
• Refusal to be registered on the National Volunteers Data file
• Disliking butter, margarine, cheese, biscuits and/or vegetable oil
• Dietary habits unreliable to controlled food intake
• Being in exclusion on the National Volunteers Data file