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

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.