Effect of Macrocomposition on Nonalcoholic Fatty Liver Disease (NAFLD) in Bariatric Surgery Candidates

Primary Outcome Measures:

• Determine the efficacy of a low carbohydrate vs. a conventional low fat diet to reduce hepatic steatosis [ Time Frame: 8-9 weeks ]
  
• Compare differences in weight loss with a 2 month hypocaloric conventional low fat vs. low carbohydrate diets in individuals who are candidates for laparoscopic Roux-en-Y gastric bypass surgery or adjustable laparoscopic banding surgery [ Time Frame: 8-9 weeks ]
  

The obesity epidemic has lead to increased morbidity and morality from cardiovascular disease and Type 2 diabetes. One co-morbidity of obesity is nonalcoholic fatty liver disease (NAFLD), which is characterized by excess fat deposition in the liver. About a third of the overweight and obese population has NAFLD and this rises to 80 to 90% of morbidity in obese patients. Short-term weight loss and caloric restriction leads to a reduction in hepatic fat content, suggesting an ability of the liver to quickly respond to dietary interventions. Manipulation of the diet macronutrient composition in order to achieve quicker weight loss as well as improve adverse metabolic consequences attributable to excess weight has attracted much attention and controversy. Multiple clinical studies have shown that low carbohydrate diets can provide more rapid weight loss in individuals in the short-term and that most have no trouble adhering to the diet for up to 6 months. Most bariatric surgery programs use a conventional low fat, calorie restricted diet during the preparation phase for surgery. However, no systematic comparison of diets with different macronutrient compositions have been performed. In this study we propose to compare the clinical effects of a low carbohydrate versus a low fat diet in individuals which can derive an immediate benefit from interventions that have the potential to reduce hepatic fat content: individuals that are preparing for bariatric surgery (laparoscopic Roux-en-Y gastric bypass surgery or adjustable laparoscopic gastric banding). Enlarged steatotic livers increase the operative risk of bariatric surgery and weight loss prior to bariatric surgery has been shown to reduce operative risk. We hypothesize that the use of a 1000 to 1200 kcalorie low carbohydrate diet (< 15% of total kcaloric intake) during the preparation phase for bariatric surgery will cause a greater reduction in weight, hepatic fat content and hepatic volume compared to a "conventional" 1000 to 1200 kcalorie low-fat diet (30% fat, 60% carbohydrates of total kcaloric intake) and offer clinical advantages by making the technical aspects of surgery easier. Thus, the data collected will provide significant new clinical insights into the effect of diets with different macronutrient composition. These results will provide a basis for larger clinical trials to identify the optimal dietary intervention to make bariatric surgery safe and effective for the increasing numbers of patients opting for this aggressive therapy for morbid obesity.