Twenty non diabetic patients (men and women) on maintenance hemodialysis for more than six months, aged of 30 to 70 years, will be included: 10 obese (BMI ≥ 30) and 10 non obese patients (18.5 <BMI <25) will be compared with 20 healthy volunteers (men and women) aged 30 to 70 years, obese and non obese, according to the same criteria.