Inclusion Criteria:  Patient eligible for bariatric surgery (according to HAS criteria) whose sleeve gastrectomy is scheduled Patient with morbid obesity (BMI ≥ 40) Age ≥ 18 years and ≤ 65 years Haemoglobinemia ≥ 12 g/dL in men and ≥ 11 g/dL in women Patient speaking and understanding French Adult having read and understood the information letter and signed the consent form Woman of childbearing age with effective / very effective contraception (Cf. CTFG) (estrogen-progestin or intrauterine device or tubal ligation) prior to surgery and a negative -HCG blood pregnancy test at inclusion, for the duration of the study Postmenopausal woman: confirmatory diagnosis (non-medically induced amenorrhoea for at least 12 months prior to the inclusion visit) Patient affiliated with, or beneficiary of a social security (health insurance) category  Exclusion Criteria:  Contraindication to bariatric surgery detected during the preoperative assessment Medical contraindication to a restrictive diet Type I or II insulin-requiring diabetes Severe renal insufficiency defined by a blood filtration rate < 30 mL/min Person wearing a pacemaker or any other implant with the same functions (cochlear implant, bladder battery, etc.) Person deprived of liberty by an administrative or judicial decision or person placed under judicial protection / sub-guardianship or curatorship A history of illness or psychological or sensory abnormality likely to prevent the subject from fully understanding the conditions required for participation in the protocol or to prevent him/her from giving informed consent