1. Introduction
NAFLD is a chronic condition that develops due to an excessive accumulation of fat in the liver. It is a heterogeneous disorder that encompasses a range of liver diseases with varying degrees of severity, clinical characteristics, and outcomes. This spectrum includes isolated steatosis, which is defined as the accumulation of lipids in 5% or more of hepatocytes, as well as nonalcoholic steatohepatitis (NASH), which is characterized by liver inflammation and hepatocellular injury. In some individuals, NASH can progress to liver fibrosis, cirrhosis, and hepatocellular carcinoma [
1]. Histological features of NAFLD also vary, including degrees of steatosis, inflammation, ballooning, and fibrosis. Predicting the disease trajectory in individual patients is a significant clinical challenge due to these variations.
The heterogeneity of NAFLD is multifactorial, stemming from a complex interplay of genetic and environmental factors, underlying pathophysiological mechanisms, and coexisting medical conditions, especially obesity, insulin resistance, and metabolic syndrome [
2,
3,
4,
5]. This diversity has significant clinical implications that can affect the diagnosis, prognosis, and treatment of NAFLD [
6]. For instance, some patients may rapidly progress to advanced stages of the disease, while others may remain stable or even improve over time [
7]. Therefore, a personalized approach to NAFLD diagnosis and management is essential, one which considers the various subtypes and stages of the disease and individual risk factors and characteristics of each patient.
The prevalence of non-alcoholic fatty liver disease (NAFLD) is on the rise globally, with up to one-third of adults in Western countries affected, and even higher rates among individuals with obesity, type 2 diabetes, and metabolic syndrome [
5]. Following menopause, women are at an increased risk for developing both NAFLD and advanced NASH fibrosis, with a prevalence that is comparable to, or even higher, than that in men of the same age [
8,
9,
10]. While NAFLD is generally more prevalent in men, there has been a significant increase in its prevalence among women over the past decade [
11], with women experiencing a steeper annual rate increase [
12] and higher mortality rate compared to men [
13]. Notably, NASH has emerged as the leading reason for liver transplantation in women [
14].
Because NAFLD is closely linked with obesity and insulin resistance [
15], lifestyle modifications are the most effective approach to treating the condition. Specifically, reducing caloric intake, limiting consumption of simple sugars and saturated fats, and increasing physical activity levels to promote weight loss and improve metabolic parameters are recommended as the first-line therapy for NAFLD patients [
16,
17]. Controlling underlying metabolic conditions such as diabetes, hypertension, and hypercholesterolemia can further decrease the risk of NAFLD. Modest weight loss, representing only 5-10% of body weight, has been shown to reduce liver fat and improve liver function [
18,
19], even in individuals with a normal body weight [
20,
21].
While it may seem reasonable to expect that lifestyle modifications resulting in weight loss and improved metabolic parameters in postmenopausal women would lead to reductions in liver fat content, there are limited studies that investigate the role of diet in NAFLD. A recent randomized dietary intervention trial discovered that both Paleolithic (high intake of vegetables, fruit, nuts, eggs, fish, and lean meat, while excluding refined sugar, salt, dairy products, and grains) and conventional low-fat diets (high intake of fruit, vegetables, whole grains, and fish, with low-fat meat and dairy products) resulted in around a 50% reduction of liver fat in healthy postmenopausal women with obesity [
22]. In a post hoc analysis of 4162 postmenopausal women from the UK Women’s Cohort Study, higher adherence to the Mediterranean Diet, which is the recommended dietary pattern for all NAFLD patients [
23], was associated with a smaller increase in waist circumference and a reduced risk of abdominal obesity in postmenopausal women with overweight [
24]. A cross-sectional analysis of 2000 women revealed that greater adherence to the Mediterranean Diet was linked with a reduced risk of metabolically unhealthy obesity in postmenopausal women; this association was not observed in premenopausal women [
25]. However, a different study found that adherence to this diet had a favorable impact on hepatic steatosis in both postmenopausal and premenopausal women, albeit with a stronger effect observed in the latter [
26].
There are several factors that contribute to the complex heterogeneity underlying NAFLD that are particularly relevant in postmenopausal women. These include hormonal status, age, lifestyle factors, genetic factors, and gut dysbiosis (
Figure 1). Hormones, especially sex hormones, have been shown to influence the development and progression of NAFLD, with the decline in estrogen levels after menopause contributing significantly to disease risk [
27]. Increasing age is also an important factor that can affect the natural history of NAFLD in this population, as older individuals are more likely to have comorbidities that can exacerbate the disease [
28,
29]. Moreover, age-related changes in metabolism and hormone levels can also contribute to the progression of NAFLD [
30]. Other hormonal imbalances, such as those observed in polycystic ovary syndrome (PCOS), are known to increase the risk of NAFLD [
31]. Lifestyle factors such as diet, exercise, and alcohol consumption can interact dynamically with other factors to affect the development and natural history of NAFLD in all individuals, including postmenopausal women [
32]. Metabolic health is a critical factor in the development and progression of NAFLD, with comorbidities such as insulin resistance, dyslipidemia, and metabolic syndrome increasing the risk of developing and progressing to NASH [
33].
NAFLD is a moderately heritable condition [
34] and several common genetic variants have been consistently associated with risk of NAFLD across diverse populations [
35]. Genetic factors can also influence the presentation of NAFLD in postmenopausal women. For instance, the rs738409 variant in the patatin-like phospholipase domain-containing protein 3 gene (
PNPLA3) has been found to significantly modulate the relationship between dietary intake and fibrosis severity in a dose-dependent, genotype-specific manner. Specifically, carriers of the variant allele were more affected by dietary factors such as carbohydrate, n-3 polyunsaturated fatty acids, isoflavones, methionine, and choline [
36]. Likewise, variants in the phosphatidylethanolamine N-methyltransferase gene (
PEMT) can worsen the effects of insufficient choline intake on NAFLD risk in postmenopausal women [
37]. Additionally, epigenetic modifications contribute to heterogeneity in the manifestation of NAFLD. For example, Sokolowska et al [
38] recently found that changes in the blood methylomes of NAFLD patients in response to a Mediterranean diet were correlated with improvements in hepatic steatosis and could stratify liver biopsies by fibrosis grade.
Gut dysbiosis, or alterations in the gut microbiome, is another factor known to contribute to the development and progression of NAFLD. Dysbiosis can lead to an increase in gut-derived endotoxins, triggering inflammation in the liver and contributing to the disease [
39]
Due to the complex and multifactorial nature of NAFLD in postmenopausal women, the disease can present as different subtypes, with varying levels of clinical presentation, diverse pathological mechanisms, and treatment responses. By recognizing the significant heterogeneity of NAFLD in postmenopausal women, we can identify specific subsets of individuals who may benefit from targeted nutritional interventions. In this review, we sought to explore the increased risk of NAFLD in postmenopausal women, and examine the current evidence supporting the role of three specific nutritional factors—choline, soy isoflavones, and probiotics – as potential nutritional adjuvants in the prevention and treatment of NAFLD.