Medicina basada en la evidencia: nutrición en la obesidad

The mainstay of the therapeutic approach to obesity is the low calorie diet. In most controlled studies the distribution of micronutrients in the diet does not seem to influence weight loss. Thus, for example, low carbohydrate diets achieve significant weight loss compared with low-fat diets in short periods (6 months), but there are no differences after longer follow-up (12 months). There is general consensus that a reduction of between 500 and 1,000 kcal daily with respect to the normal diet achieves an average weight loss of 0.5 to 1 kg per week for the first 6 months of treatment, representing a reduction of 5-10% of body weight, a proportion that is sufficient to attenuate the impact of obesity-related comorbidities. However the long-term results (more than 1 year) with low-fat diets are discouraging (0-3 kg), while the safety of low carbohydrate diets remains to be demonstrated. The present review analyzes the levels of evidence for the effect of distinct types of diet (including very low calorie diets) on body weight in the medium and long term, highlighting that possibly the therapeutic approaches to weight loss should differ from the strategies used to maintain weight loss. Lastly, whatever the dietary approach to obesity, there is no doubt that reinforcement through a structured program of lifestyle changes and physical activity is an essential tool to ensure longterm success.