An intervention study design in 90 obese patients will be used. Nutritional, metabolic and psychological status as well as gut microbiota will be evaluated before gastric bypass and 6 months post surgery. During this period of 6 months, all patients will receive a specific diet according to recommendation with regard to bariatric surgery.

Subjects will be than randomized in 2 sub-groups:

A. patients receiving a standard healthy diet without micro-nutriments' supplementation; B. patients receiving a healthy diet and probiotics, minerals, aminoacids, omega-3 acids vitamin and mineral supplementation

The primary aim of the study is to analyse the micro-nutritional status in morbidly obese patients before and 6 months after bariatric surgery (Roux-en-Y gastric bypass, RYGB). The secondary outcome will be the impact of 6 months probiotics, minerals, aminoacids, omega-3 acids and vitamin supplementation on microbiota, metabolic and psychological parameters 12 months post-RYGB.

An intervention study in 90 obese patients (BMI>40 kg/m2) will be used. Nutritional, metabolic and psychological status as well as gut microbiota will be evaluated before gastric bypass and 6 months post RYGB. During this period of 6 months, all patients will receive a specific diet according to recommendation with regard to RYGB.

Subjects will be than randomized in 2 sub-groups:

A. patients receiving a standard healthy diet without micro-nutriments' supplementation; B. patients receiving a healthy diet and probiotics, minerals, aminoacids, omega-3 acids vitamin and mineral supplementation Healthy diet will be defined as follow: 9-15% of proteins, 50-55% of carbohydrates and 30-35% lipids (25% saturated fat, 50% mono-unsaturated fat and 25% poly-unsaturated fat).

The following parameters will be analysed before RYGB and 6 months and 12 months post RYGB, respectively:

• Nutritional status with oxidative stress parameters (Vitamins A and E, Selenium, Zinc, Copper, Glutathione peroxidise, Superoxide dismutase and Iron)
• Metabolic parameters (Total cholesterol, LDL-cholesterol, HDL-cholesterol, Triglycerides, fasting glucose and insulin, CRP)
• Fatty acids (linoleic acid, alpha-linoleic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)
• Gut microbiota
• Psychological status (anxiety, depression and quality of life as evaluated by validated questionnaires).

Inclusion Criteria:

• Obesity BMI>40 kg/m2

Exclusion Criteria:

• Antidepressant treatment