Background: Surgery is the only effective treatment for people with a body mass index (BMI) greater than 40 Kg/m² or even greater than 35 Kg/m² when some diseases like diabetes or hypertension appear. In order to minimize surgical risk and improve postoperative results, preoperative preparation it's very important. "Acute" preoperative weight loss just before surgery plays a crucial role in that preparation and can be achieved through different ways like a low calorie diet, a very low calorie diet or with the use of an intragastric balloon. The advantages or particularities of every one of them will be summarized in this article. Material and methods: Literature review of the benefits, risks and complications of preoperative weight loss through a low calorie diet, a very low calorie diet or intragastric balloon placement. Results: Seven of thirteen initially selected reports from Medline search were considered relevant, including a total 371 patients (240 patients treated with low calorie diet, 90 with very low calorie diet and 41 cases of intragastric balloon placement). We found that weight loss was greater in patients with very low calorie diets and intragastric balloon groups but with a slightly increase in morbidity and cost. Conclusion: Although there are no comparative studies, data from the literature results show that diets very low in calories are more effective and require less time than low-calorie diets and cheaper with fewer side effects than the intragastric balloon.