Diets and nonalcoholic fatty liver disease: the good and the bad.

Nonalcoholic fatty liver disease (NAFLD) is now described as the hepatic manifestation of the metabolic syndrome and is the most frequent chronic liver disease, affecting about one out of three people in the western world. NAFLD is strongly linked to insulin resistance, which represents a key risk factor for the development of type 2 diabetes. To date, there are no reliable and efficient pharmacotherapies in the treatment of NAFLD. However, obesity, which represents one of the main features of the metabolic syndrome, is strongly associated with NAFLD. Therefore, lifestyle modifications, i.e. weight loss and increased physical activity, are the very first clinical approaches aiming at treating NAFLD. However, although weight loss is beneficial in NAFLD, certain diets known to induce weight loss can actually cause or exacerbate this disease, and therefore induce insulin resistance, such as very low carbohydrate, high fat diets. Moreover, macronutrient diet composition can impact NAFLD without any change in body weight. Indeed, diets rich in fatty acids, particularly saturated, or in refined carbohydrates such as those found in soft drinks, can actually exacerbate NAFLD. The aim of this review is to discuss the role of weight loss and macronutrients modifications, particularly the role of fat and carbohydrate diet composition, in the treatment of NAFLD.