OBJECTIVE Bariatric surgery is considered the only therapeutic alternative for morbid obesity and its comorbidities. High risks factors are usually linked with this kind of surgery. In order to reduce it, we consider that losing at least 10% of overweight in Morbid Obese (MO) and a minimum of 20% in Super- Obese patients (SO) before surgery, may reduce the morbidity of the procedure. The aim of our study is to demonstrate the effectiveness and tolerance of a balanced energy formula diet at the preoperative stage, comparing it against a low calorie regular diet. METHOD We studied 120 patients divided into two groups of 60 each, group A was treated 20 days prior to bariatric surgery with a balanced energy formula diet, based on 200 Kcal every 6 hours for 12 days and group B was treated with a low calorie regular diet with no carbs or fat. The last eight days prior to surgery both groups took only clear liquids. We studied the evolution of weight loss, the BMI, as well as behavior of co-morbidities as systolic blood pressure, diastolic blood pressure, glucose controls and tolerance at the protocol. RESULTS The study shows that patients undergoing a balanced energy formula diet improved their comorbidities statistically significant in terms of decrease in weight and BMI loss, blood pressure and glucose, compared to the group that was treated before surgery with a low calorie regular diet. Nevertheless both groups improving the weight loss and co-morbidities with better surgical results and facilities. CONCLUSION A correct preparation of the Morbid Obese patients prior of surgery can reduce the operative risks improving the results. Our study show that the preoperative treatment with a balanced energy formula diet as were included in our protocol in patients undergoing bariatric surgery improves statistical better their overall conditions, lowers cardiovascular risk and metabolic diseases that the patients with regular diet alone.