Diet Therapies for the Treatment of Non-alcoholic Fatty Liver Disease (NAFLD): A Systematic Style Review

Abstract

Background: The prevalence of NAFLD is increasing in line with rates of obesity; it is currently estimated to affect 25% of the western world [1]. In the absence of approved pharmaceutical therapy, lifestyle intervention is the mainstay of current treatment [2]. Establishment of effective treatments is imperative to improve quality of life for patients with NAFLD and reduce the burden on health services. Aim: To determine the most effective dietary interventions in the treatment of NAFLD. Methods: Medline, Embase and Web of Science were searched by one reviewer to select studies investigating the effects of a specific dietary intervention on markers of NAFLD which were subsequently assessed for quality using an adapted Newcastle Ottawa Scale. Markers of liver function and anthropometrics were used to compare the effects of the interventions. Inclusion criteria included English language, human studies recruiting participants aged >16 years; original research published in the past 10 years were used to ensure up-to-date evidence.  Results: 10 studies meeting the inclusion criteria were included in this review 7 of which explored the effects of weight loss, 2 investigating omega-3 supplementation and 1 studying liquorice root extract. Larger weight losses were not associated with greatest improvements in liver function. The greatest reduction in ALT (-62.0 IU/L), was associated with an energy intake of 126kJ/kg/day alongside an iron restriction of <6mg/day. Both omega-3 and liquorice supplementation reduced ALT levels by 30.7IU/L and 12.8IU/L, respectively, in the absence of weight loss.  Discussion: Trends in weight loss data suggest that nutrient composition may be more significant than energy content of the diet. Animal studies have uncovered a link between iron accumulation and hepatic damage caused by reactive oxygen species supporting results recorded by Yamamoto et al. [3]. The anti-inflammatory properties of omega-3 oils are thought to reduce markers of NAFLD similar to their role in cardiovascular disease [4]. Omega-3 supplementation appeared more effective when combined with weight management. Combination therapy may be more beneficial given the relationship with NAFLD, obesity and other associated metabolic disorders.  Conclusion: Weight loss, omega-3 supplementation and liquorice extract are effective in reducing markers of NAFLD; combination therapy may be more successful than isolated dietary changes. Diet therapy has the potential to provide a cost effective treatment option in targeting the increasing population of patients with NAFLD and its co-morbidities. Dietary interventions have demonstrated significant reductions in clinical markers of the disease such as ALT (-62.0 IU/L p=0.001) (Yamamoto et al., 2007). Whilst iron restriction alongside weight loss appeared effective, the impact on general health is unknown; further research is therefore required in this area.