1. Introduction

The worldwide prevalence of nonalcoholic fatty liver disease (NAFLD) has increased along with that of obesity over the last decades. In fact, the global prevalence of NAFLD is around 25%, and it has become the most prevalent chronic liver disease in Western countries due to its strong association with obesity ^[1][2]. The rise in the prevalence of these conditions seems to be largely explained by the exposure to an “obesogenic” environment. This complex and multidimensional scenario is composed by diverse factors that promote an individuals’ overall energy imbalance (i.e., towards a sustained positive energy balance) such as increased availability (food supply) and overconsumption of low-nutrient, energy-dense foods, the modern sedentary lifestyle, among others, leading a state of excess adiposity ^[3][4]. Obesity represents the centerpiece in the development of several metabolic complications such as insulin resistance, diabetes mellitus type 2 (T2DM), cardiovascular disease (CVD), and NAFLD ^[2][5]. The latter is a multifactorial metabolic disorder in which excessive intrahepatic fat accumulation is the hallmark feature. Occasionally, liver fat is accompanied by inflammation that causes more drastic morphological changes in the liver tissue ^[6]. It is important to remark that besides over-nutrition, certain types of undernutrition paradoxically may promote the development of fatty liver ^[7].

NAFLD encompasses a wide spectrum of liver damage that is categorized by histological examination. The least advanced stage of disease, simple steatosis (SS), is characterized by steatosis alone (defined as >5% hepatocytes containing lipid vesicles). Nonalcoholic steatohepatitis (NASH), which represents a more severe form of NAFLD, is defined by the presence of marked inflammation and hepatocyte ballooning with or without fibrosis ^[6]. NAFLD is a progressive disease, in which chronic hepatic inflammation is involved in the evolution of NASH to cirrhosis that represents a risk factor for the development of hepatocarcinoma ^[8].

Healthy lifestyle modifications, namely diet and physical activity, are the mainstay of the NAFLD therapy ^[9][10][11]. NAFLD is part of a complex network of metabolic disruptions in multiple tissues commonly associated with obesity ^[12], which consequently makes diet therapy a difficult endeavor. The present tendency of nutritional intervention leans towards on correcting unhealthy dietary factors that promote disease progression. Currently, the optimal nutritional management remains controversial, although there is general consensus that gradual body weight loss is the recommended standard of care for the treatment of NAFLD. Dietary energy restriction is a key element to achieve weight reduction, but its compliance depends largely of self-control, and consequently, diet adherence might become quite challenging in most cases. Hence, different choices of nutritional interventions have been explored in the NAFLD context.

2. Future Perspectives in the Nutritional Management of NAFLD

NAFLD is a growing global public health issue that affects adult and pediatric populations and it is expected to worsen in the upcoming years due to its close association with the obesity epidemic and other obesity-related metabolic unhealthy phenotypes. Since nutritional therapy is fundamental in NAFLD management, it should be oriented to prescribe individualized high quality healthy diets instead of aiming at weight loss per se. Indeed, NAFLD management has long been focused on weight reduction mainly through low-energy dietary intervention with or without modified macronutrient distribution. This, in fact, is intended to gradually decrease low-grade chronic inflammation given that higher adiposity can be pinpointed as a major component of metabolic disorders. However, long-term adherence to low-energy diets is still a troubling issue due to two reasons: first, there is usually little attention or no further guidance on how to sustain the achieved benefits for an individual’s health over the years. Secondly, sustaining a high level of adherence in diets including alternative macronutrient distribution over months or even for years is virtually impossible for most individuals. Besides, promoting a reduced intake of one macronutrient for a long period of time might lead to other nutrient deficiencies (e.g., fiber intake could be compromised in carbohydrate-restricted diets as well as some vitamins contained in whole grains and green leaves such as thiamine, riboflavin, niacin and folate) that might worsen digestive or even metabolic functions if these are overlooked. Thus, it is advisable that the nutritional guidance from nutritionists includes foods with high fiber-net carbohydrates ratio (e.g., avocado, nuts, as well as chia seeds and flaxseeds).

Alternatively to dietary restriction, certain dietary patterns have shown promising results with a high degree of clinical relevance. These patterns are based on food selection considering high quality foods. Indeed, nutrient replacement founded on whole grain choices instead sugary foods or drinks have long been part of certain cultures, such as the MedDiet. This dietary pattern, for instance, has been widely acknowledged for the doubtless cardiovascular benefits it provides. However, not all countries would be able to initiate it, let alone adhere to a dietary pattern that might not share anything in common with local food production and traditional cuisine, which are deeply rooted into the history of different human cultures. Of course, it is not an availability issue what we wish to stress out here, but rather a cultural barrier that may represent a great challenge for many geographically distant populations when trying to adapt to different food choices.

Taken together the previous considerations, the “one-size-fits-all” idea is unable to be replicable on this matter as it has been in many other clinical nutritional areas. Therefore, it is important that the upcoming dietary clinical guidelines for NAFLD takes the cultural background into consideration before pushing for straightforward dietary interventions. In fact, a local and sustainable diet will always be preferred over new proposals because of the psychological, social, and economic positive impact it produces. Finally, a large number of foods, regardless of their origin, may be a source of antioxidants and other phytonutrients that enhance or inhibit certain cellular processes. In fact, there is a pipeline of understudied foods and food components that might do the job as well when prescribing strategic dietary plans. Thus, we are convinced that the health-regaining process through diet modification in NAFLD management should play more attention on the local sources of high-quality foods and a bit less in the calorie count.