Nonalcoholic fatty liver disease (NAFLD) is a significant health problem and affects 100 million adults in the United States (30% of the adult population), and an estimated 20% of these individuals have the most severe form of NAFLD—nonalcoholic steatohepatitis (NASH). A program targeting gradual weight reduction and physical exercise continues to be the gold standard of treatment for all forms of NAFLD.
Note: Only the Mediterranean diet reduces steatosis
This research was published in the American Journal of Clinical Nutrition
The study is quite long but here is a link to the original article
Comparative review of diets for the metabolic syndrome: implications for nonalcoholic fatty liver disease
If you choose to read the report notice that it was published in 2007 so quite a few narrow studies have been done since then that support the value of olive oil as the key unsaturated fat but here is part of the summary.
SPECIFIC RECOMMENDATIONS AND FUTURE DIRECTIONS
Taking into account the evidence discussed in this article, the authors recommend a highly individualized approach for the dietary treatment of NAFLD and NASH based on a thorough assessment of individual metabolic, physiologic, and nutritional status and personal goals and preferences. The effects of each diet discussed in this article on specific health indexes, such as blood triacylglycerol concentration and insulin sensitivity, are shown in Table 1⇓ and are based on a review of the references included in this article. The composition and the relative macronutrient content of each diet are shown in Table 2⇓. Most NAFLD patients would benefit from the guidelines given below.
Moderate calorie restriction of ≈100–500 kcal/d through a decrease in portion sizes is recommended by the American Dietetic Association and the America on the Move program . Evidence of beneficial effects from weight loss through surgical methods in obese patients with NAFLD suggests that weight reduction through dietary means would also have positive effects. Specifically, weight loss resulted in a significant decrease in the prevalence of the metabolic syndrome and marked improvements in liver steatosis, inflammation, and fibrosis. However, very few studies examining the effects of different dietary and lifestyle approaches in achieving weight loss in NAFLD have been done, and further studies are urgently needed.
NASH patients have a higher postprandial triacylglycerol response and an increased production of large VLDL detected by an oral fat load compared with controls, despite normal fasting blood lipid concentrations, which suggests that the metabolism of dietary fat is impaired in these individuals (37). Decreased total fat consumption could lead to a decrease in postprandial lipemia and the associated disruptions in lipid metabolism. Further studies are needed to ascertain whether the consumption of smaller meals that are lower in total fat may be helpful in NAFLD patients.
Regular, moderate exercise is independently associated with a 25–35% decrease in CHD risk over a 20-y period (167), regardless of diet and other risk factors. An exercise strategy of walking a distance of 2 miles, 3 d/wk, at a target heart rate of 60% of heart rate reserve (as measured by peak oxygen uptake) resulted in increases in HDL and fitness equivalent to a more rigorous exercise program of walking 3 miles, 3 d/wk, at 80% of heart rate reserve (168). Further studies are needed to elucidate the effects of specific exercise strategies in the NAFLD and NASH populations.
n−3 Fatty acid intake—specifically DHA and EPA—has been shown to improve CHD risk by affecting metabolic variables such as blood triacylglycerol concentrations and through independent mechanisms related to antiarrhythmic effects. α-Linolenic acid from walnuts also improves blood lipid profiles. Furthermore, n−3 fatty acids have been found to decrease steatosis in both preliminary trials in humans and in animal models. More studies are needed to clarify the specific dosages, formulations, and effects of n−3 fatty acids in individuals with NAFLD.
Beneficial effects on both insulin sensitivity and lipid markers have been found in response to low-GI carbohydrates and high-fiber intakes from fresh fruit, vegetables, legumes, and grains. A reduction in the amount of total carbohydrates, especially simple sugars, would reduce the total pool of acetyl CoA in the liver and, therefore, reduce the flux through the DNL pathway. The reduction in fatty acid synthesis would also result in reduced triacylglycerol synthesis and prevent the excess accumulation of total fat in the liver. A reduction in the rate at which glucose enters the bloodstream, via the consumption of lower-GI carbohydrates and higher amounts of fiber, would also reduce the subsequent exaggerated insulin excursions and thereby reduce insulin resistance. However, nutritional studies of the specific effects of modulating carbohydrate type and quantity on insulin resistance and disease progression in NAFLD patients are needed.
The intake of diets that are lower in carbohydrate, lower in saturated fat, but higher in protein than the average American diet—which consists of ≈47% carbohydrate, 38% fat (20% SFA), and 15% protein—tend to be beneficial for ameliorating features of the metabolic syndrome, including effects on insulin sensitivity and blood lipids. Certain individuals may be susceptible to renal malfunction associated with high protein intakes; therefore, an increase in total protein intake may not be appropriate in these patients. Studies are needed to examine the effects of modifying the protein content in NAFLD patients.
An emphasis on MUFAs from foods such as olive oil, in favor of high-SFA foods such as fatty meats and full-fat dairy products, is advisable because SFAs have deleterious effects on liver function and raise blood LDL concentrations, whereas MUFAs are beneficial in reducing the risk of CHD and type 2 diabetes through effects on blood lipids, endothelial function, and insulin sensitivity.
The recommendation to avoid the intake of sodas and other sweetened drinks is substantiated by observations that high fructose intakes, high sucrose intakes, or both can induce DNL, which leads to higher blood triacylglycerol concentrations and lower insulin sensitivity. Soda consumption contributes a substantial proportion of the calorie intake in many overweight and obese individuals. A reduction in the consumption of simple sugars, especially in the form of sweetened beverages, which provide sugar in a very accessible and easily absorbable form, would help to reduce the exaggerated glucose and insulin excursions that are associated with insulin resistance. In addition, a reduction in the consumption of sweetened beverages would lead to a reduction in total calories consumed, which would facilitate weight loss.
Poor adherence in weight loss and lifestyle modification is a crucial issue in overweight and obese individuals. Weight loss through diet and exercise tends to be successful in the first 6 mo, but in the long-term, most individuals are unable to maintain this weight loss. Strategies to improve adherence and long-term behavioral modification are therefore imperative for the successful treatment of NAFLD through dietary approaches.