March 2012

The Role of Diet and Nutrient Composition in Nonalcoholic Fatty Liver Disease

Erin Marie McCarthy, MS, RD, LDN; Mary E. Rinella, MD

Nonalcoholic fatty liver disease (NAFLD) affects about 70 million adults in the United States which is an alarming 30% of the adult population. According to the authors, the term NAFLD includes a spectrum of liver disease that ranges from steatosis (fat accumulation in hepatocytes) to nonalcoholic steatohepatitis (NASH) which is a more progressive type of liver disease. It is estimated that around 20% of those with NAFLD have NASH which can lead to cirrhosis and the need for a liver transplant. Patients with NAFLD of both forms typically display signs of metabolic syndrome including dyslipidemia, central obesity, hypertension, and insulin resistance (IR). Excess body weight is also common factor for patients with NAFLD.

Obesity causes a chronic, inflammatory condition that is the result of a failure in normal homeostatic regulation of energy intake, storage, and use. In the state of obesity, visceral adipose tissue is expanded and becomes filled with inflammatory cells causing proinflammatory cytokines to increase. This eventually leads to steatosis in the liver, increased insulin sensitivity and increased injury from oxidative stress. Weight loss in these patients can reverse many of the consequences. Therefore, according to McCarthy and Rinella, sustained weight loss is the most effective treatment for NAFLD and should be the base of any treatment plan.  Dietary macronutrient content may also be a factor in reducing the effects of NAFLD.

This article discusses the current data on the effects of diet-induced weight loss and dietary composition. Articles cited in the review were identified through an electronic data base search using PubMEd. Randomized control trials, case control studies, and observational studies of adult patients were included.

The liver is not meant to store fat but when energy intake does not equal energy output, it can result in accumulation of fat in the liver. Patients with NAFLD have been shown to have higher energy intake than healthy control groups. Long term studies are limited but the consensus is that long term well controlled dietary intervention including physical activity, is effective in improving NAFLD because it improves insulin sensitivity, hypertension, and dyslipidemia. Several studies show that diet induced weight loss also reduces liver enzymes and hepatic steatosis.

In the largest randomized control trial reviewed for this study, patients were randomized 2:1 to a combination of diet, exercise, and behavior modification (lifestyle intervention) or a control group. The goal was to achieve a 7-10% weight reduction and the primary outcome measure was an improvement in the NAFLD activity score after 48 weeks of treatment. Participants in the lifestyle intervention group were given an energy intake goal based upon their starting weight. They were instructed to consume 1000-1200kcal/day if less than 200lb and 1200-1500kcal/day if greater than 200lb. They were also told to consume a diet consisting of no more than 25% fat. Participants in the control group attended sessions that provided basic education on NASH along with healthy eating and physical activity tips. The lifestyle intervention group had an average of 9.3% weight loss compared to a 0.2% loss in the control group. The lifestyle intervention group also scored higher on the NAFLD activity test and experienced significant improvements steatosis.

Caloric restriction has been shown to be effective in the treatment of NAFLD yet dietary composition can directly influence the development of NAFLD. There is evidence that manipulation of micronutrient and macronutrient content can affect hypertension, inflammation, lipid levels, and insulin resistance independent of weight loss. Based on data retrieved for this review, a diet that is lower in carbohydrates and saturated fat and higher in lean protein, fiber, and omega 3’s is likely to be beneficial.

The use of probiotics in participants was briefly mentioned in the article. Probiotics are defined as live microbial food supplements (components of bacteria) that have beneficial effects on human health. Current evidence suggests that gut microbiota modifications may play a role in the development of nonalcoholic steatohepatitis (NASH) yet no clinical trials have been completed using probiotics for patients with NAFLD. Data from two pilot studies concluded that the use of probiotics may improve liver chemistry tests and decrease markers of lipid peroxidation.

NAFLD leads to a great deal of morbidity and mortality in the United States. While some pharmacologic therapies are gaining interest, gradual and sustained weight loss is still considered to be the best treatment. Based on this article, lifestyle modification through diet and exercise should be the foundation of treatment for anyone with NAFLD.  Macronutrient composition of the diet is also important and can be used with lifestyle modification to help reduce hepatic fat and inflammation.

McCarthy, E.M., Rinella, M.E. (2012). The Role of Diet and Nutrient Composition in Nonalcoholic Fatty Liver Disease. Journal of The Academy of Nutrition and Dietetics, 112(3), 401-409.