Elsevier

Clinical Nutrition

Volume 33, Issue 2, April 2014, Pages 186-190
Clinical Nutrition

Review
Diets and nonalcoholic fatty liver disease: The good and the bad

https://doi.org/10.1016/j.clnu.2013.11.003Get rights and content

Summary

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.

Introduction

The prevalence of nonalcoholic fatty liver disease (NAFLD) is rapidly increasing in the western countries and now affects about a third of the population.1 NAFLD is a spectrum ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) that occur mainly due to fat accumulation in the liver, but can ultimately lead to cirrhosis, which is not reversible and may progress to hepatocellular carcinoma. Therefore, NAFLD can be considered as a risk factor for cancer, but is now also recognized as a risk factor for cardiovascular diseases.2 Moreover, NAFLD is now considered to be the hepatic manifestation of the metabolic syndrome, which is characterized by insulin resistance, dyslipidemia, hypertension, type 2 diabetes and excess body weight.3, 4 In particular, patients presenting one of the metabolic syndrome features are at increased risk for the development of NAFLD compared to the unaffected ones. For instance, among morbidly obese patients, approximately 90% have NAFLD.5 The diagnosis of NAFLD is beyond the scope of this review and is discussed elsewhere.6 Because obesity strongly influences the development of NAFLD, weight loss appears as the main rational target to treat NAFLD. Indeed, to date no pharmacological therapy is approved for NAFLD, and lifestyle modifications are strongly recommended for patients with NAFLD.7 An important aspect of lifestyle is diet. The aim of this review is therefore to discuss the role of dietary interventions in the treatment, but also in the pathogenesis of NAFLD. We will first precise the pathophysiology of NAFLD and its nutritional implications will be summarized. Secondly, the potential role of some diets in the development of NAFLD will be outlined. Finally, we will examine the nutritional/dietary therapeutic approaches in the treatment of NAFLD.

Section snippets

Pathophysiology of NAFLD and nutritional implications

The pathophysiology of NAFLD is complex and multifactorial. It is mainly characterized by the accumulation of lipids. The latter may be due: 1) to excessive influx of fatty acids from endogenous fat depots (mostly white adipose tissue); 2) from excess dietary fat intake and 3) from de novo hepatic lipogenesis (Fig. 1). In animals, this net accumulation of fat in the liver, i.e. NAFLD, has been clearly linked to the development of hepatic insulin resistance.8, 9, 10, 11, 12, 13, 14, 15, 16, 17

Fatty acids

Several epidemiological studies have linked metabolic and cardiovascular diseases to altered lipid metabolism and dietary fat type, but data on the association between dietary type and fatty liver are scarce.21 A small sample size study has revealed that patients with NASH have an increased intake of saturated fat and cholesterol, and reduced dietary intake of polyunsaturated fatty acids.22 In line with these results, Toshimitsu and coworkers revealed that patients with fatty liver and NASH

Nutritional therapeutic approach: from theory to practice, effects on NAFLD

Dietary intake plays a very important role in the pathogenesis of NAFLD. Weight loss is an essential element in the therapy and treatment of this disease, although macronutrients composition seems to play an important role, as discussed above. To achieve weight loss, various approaches have been used resulting in either rapid and drastic or moderate weight loss. Historically, the very first trials experienced the effect of very low caloric diets and found that this type of diets drastically

Conclusion

NAFLD is the most frequent chronic liver disease and is mostly associated with the epidemic of obesity. NAFLD is associated with an increased risk of cardiovascular diseases and liver-related complications, such as liver cirrhosis or hepatocellular carcinoma. NAFLD is clearly associated with insulin resistance, which is a key risk factor for the development of type 2 diabetes. Current pharmacological options for NAFLD are disappointing and warrant further research. Weight loss is efficient and

Conflict of interest statement and statement of authorship

Each author has participated sufficiently, intellectually or practically, in the work to take public responsibility for the content of the article, including the conception, design, and for data interpretation. All authors have read and approved the final manuscript. MA and FRJ have no conflict of interest.

Acknowledgments

This work was supported by the Hjelt Foundation, the Olga Mayenfisch Foundation and the Fondation De Reuter.

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