Obesity is a major public health problem and is constantly on the rise. Therapeutic approaches based on dietary advice, physical activity and the management of psychological difficulties are not always sufficient to achieve a lasting weight reduction.

Bariatric surgery (or obesity surgery), accompanied by therapeutic education and adequate medical and dietary monitoring, can lead to significant and lasting weight loss. It is indicated as a second-line treatment for patients who have failed medical treatment, whose BMI is greater than or equal to 40 or whose BMI is greater than or equal to 35 with comorbidities (type 2 diabetes, arterial hypertension, obstructive sleep apnoea-hypopnoea syndrome, severe joint disorders).

The surgeon may be very bothered by the intra-abdominal fat mass and especially by steatotic hepatomegaly (increase in the size of the liver and its fat load).

Faced with this problem, various preoperative strategies such as the placement of an intra gastric balloon have been tried to decrease the size of the liver but a systematic review from 2016 indicates that a low calorie diet is preferable. Preoperative weight loss can reduce fat load and liver volume very rapidly. This meta-analysis shows that all low-calorie, high-protein diets are effective and that the optimal duration (4 weeks), compliance and tolerance are important factors for success.

Obesity is a major public health problem and is constantly on the rise. Therapeutic approaches based on dietary advice, physical activity and the management of psychological difficulties are not always sufficient to achieve a lasting weight reduction.

Bariatric surgery (or obesity surgery), accompanied by therapeutic education and adequate medical and dietary monitoring, can lead to significant and lasting weight loss. It is indicated as a second-line treatment for patients who have failed medical treatment, whose BMI is greater than or equal to 40 or whose BMI is greater than or equal to 35 with comorbidities (type 2 diabetes, arterial hypertension, obstructive sleep apnoea-hypopnoea syndrome, severe joint disorders).

The surgeon may be very bothered by the intra-abdominal fat mass and especially by steatotic hepatomegaly (increase in the size of the liver and its fat load).

Faced with this problem, various preoperative strategies such as the placement of an intra gastric balloon have been tried to decrease the size of the liver but a systematic review from 2016 indicates that a low calorie diet is preferable. Preoperative weight loss can reduce fat load and liver volume very rapidly. This meta-analysis shows that all low-calorie, high-protein diets are effective and that the optimal duration (4 weeks), compliance and tolerance are important factors for success.

However, there is no consensus on the benefit/risk balance of a preoperative diet and there is considerable variability in approach at national and international level.

The present clinical study involves a triad of dietician, surgeon, physician (endocrinologist/nutritionist or internist) to secure this diet. It could provide a database to help estimate the risk of undernutrition in the obese subject.

This diet, designed to facilitate the surgical procedure and potentially reduce intraoperative complications, is inexpensive, easily accessible and reproducible by other teams. This innovative management could standardise the preoperative management of patients undergoing bariatric surgery at national level. It would also improve the results of bariatric surgery both in the short term by reducing complications and in the long term by increasing weight reduction as reported in the Livhits meta-analysis. The risk of undernutrition should be reduced by this hypocaloric hyperprotein diet and consequently cancel out the increased risk of mortality, infections, delayed healing, longer hospital stay and the costs that this would entail.

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