Thin people also get fatty liver?

Introduction Non-alcoholic fatty liver disease (NAFLD) is one of the most common causes of liver disease, usually related to type 2 diabetes, dyslipidemia, metabolic syndrome and obesity
.

In the past, the related research on NAFLD was mostly carried out in obese people, but in recent years, it has also begun to be widely studied and reported in thin people/non-obese people
.

This article aims to summarize the prevalence, clinical manifestations, diagnosis and treatment of lean/non-obese NAFLD based on the latest literature
.

The prevalence of lean/non-obese NAFLD A recent meta-analysis showed that the overall prevalence of NAFLD in lean and non-obese populations was 10.
2% and 15.
7%, respectively
.

The results of another study involving 155,846 non-obese subjects showed that the mixed prevalence of NAFLD was 14.
5% (95% CI 12.
3-17.
1%)
.

The prevalence of NAFLD in the Western population is estimated to be about 7%-20% (19.
3% in North America; 95% CI 13.
9-26.
2), and the prevalence in the Asian population is about 5%-26%
.

The reason why the scope of the diseased population is so wide may be due to differences in the research population, diagnostic tests, life>
.

The clinical manifestations of lean/non-obese NAFLD patients with non-obese NAFLD are often asymptomatic, their condition is still undiagnosed or only accidentally discovered through imaging
.

The waist circumference and weight of non-obese NAFLD patients are generally lower than those of obese patients
.

Some studies believe that compared with obese NAFLD patients, lean NAFLD patients tend to be younger, with lower fasting blood glucose, glycosylated hemoglobin (HbA1c) levels, blood pressure, homeostasis model-assessed insulin resistance index (HOMA-IRI), and metabolic syndrome.
(MetS) The prevalence is lower and the hemoglobin level is higher
.

Compared with healthy people, non-obese NAFLD patients tend to have higher dyslipidemia, fasting blood glucose levels, body mass index (BMI), blood pressure, malondialdehyde levels, and HOMA-IRI
.

Bernhardt et al.
compared non-obese NAFLD patients and obese people without hepatic steatosis.
The results showed that the two groups of people had dyslipidemia and hypertriglyceridemia, HbA1c (within the normal range) level, and HOMA-IRI.
Significant differences, but patients with lean NAFLD have significantly higher hematocrit, hemoglobin and serum ferritin levels
.

There are many factors related to the occurrence of lean NAFLD.
In the future, further research on the genetic, metabolic dysfunction and environmental factors of lean/non-obese NAFLD patients may be able to reveal more clinical features of the disease
.

Diagnosis of lean/non-obese NAFLD NAFLD is defined as fatty degeneration in the liver.
When the secondary cause of liver fatty infiltration has been ruled out (Table 1), NAFLD can be diagnosed by histology or imaging
.

Table 1 Secondary causes of hepatic steatosis There is no difference between the diagnosis of lean and obese NAFLD in imaging studies
.

In ultrasound examination, the accumulation of fatty vesicles in the cells leads to enhanced liver parenchymal reflex, so steatosis is manifested as diffuse enhancement of liver echo or "bright liver"
.

Liver biopsy is the gold standard for the diagnosis of NAFLD, but it is only recommended for cases where other tests cannot clarify the patient's condition
.

Obese and lean NAFLD may be difficult to distinguish histologically, and the two diseases use the same definition and scoring system
.

The focus of identifying NAFLD and non-alcoholic steatohepatitis (NASH) is to detect the risk of advanced liver fibrosis early to avoid the development of liver cirrhosis and hepatocellular carcinoma
.

There are many non-invasive examination tools to help accurately diagnose liver fibrosis and stage NAFLD, such as NAFLD Fibrosis Score (NFS) and FIB-4 Index
.

A systematic review and meta-analysis showed that compared with overweight/obese subjects, lean/non-obese NAFLD patients had lighter histological features and fibrosis scores.
Another meta-analysis on NAFLD showed that, Elevated NFS levels are associated with a higher risk of death
.

Therefore, lean/non-obese NAFLD patients may have a lower risk of death than obese patients
.

Other non-invasive examination tools include: shear wave elastography, transient elastography and magnetic resonance elastography
.

Among them, magnetic resonance elastography has the best predictive performance
.

These non-invasive methods are necessary tools for accurate diagnosis and monitoring of liver fibrosis, as well as risk stratification tools and treatment endpoints in clinical trials
.

Treatment of lean/non-obese NAFLD At present, there are no specific treatment guidelines for non-obese NAFLD
.

Although lean NAFLD patients are within the normal weight range, the occurrence of non-obese NAFLD is associated with weight gain
.

A population-based intervention study involving Asian patients with a BMI of less than 25 kg/m2 showed that 97% of patients who successfully lost more than 10% of their weight and about 40% of patients who lost 3% to 5% of patients experienced NAFLD regression
.

In addition, Jin et al.
enrolled 120 potential living liver donors with liver steatosis ≥30% and had undergone a baseline liver biopsy (95% of the subjects had a BMI of less than 30).
After a 10-week follow-up, the biopsy confirmed that dietary adjustment, Exercise and weight loss improved the steatosis in 85.
8% of the subjects
.

A randomized controlled trial (RCT) on life>
.

However, this correlation has not been confirmed by studies only in lean patients
.

The latest EASL-EASD-EASO clinical practice guidelines recommend the Mediterranean diet as the preferred diet for all NAFLD patients
.

The Mediterranean diet mainly increases the intake of omega-3 and monounsaturated fatty acids, and reduces the intake of carbohydrates (mainly refined carbohydrates and sugars)
.

Even if adherence to the Mediterranean diet does not reduce weight, it will result in a significant reduction in liver steatosis, which is a meaningful treatment for lean NAFLD patients
.

However, only small-scale and short-term test results support this theory, and further long-term studies are needed to verify it
.

A number of studies and systematic reviews have shown that drinking coffee has a protective effect on NAFLD
.

However, the effect of coffee as a preventive or therapeutic measure has not been specifically studied in lean NAFLD
.

Increased physical activity has a beneficial effect on NAFLD, and its effect is not affected by the degree of weight loss
.

Li et al.
demonstrated the benefits of physical activity in a dose-dependent manner, which means that regardless of energy intake and sedentary time, moderate and vigorous physical activity have a beneficial effect on NAFLD
.

The EASL-EASD-EASO guidelines recommend that patients perform moderate-intensity aerobic physical activity 3-5 times a week for a total of 150-200 minutes/week
.

However, there are no specific guidelines or clinical evidence for physical activity in patients with lean NAFLD
.

In summary, it is recommended that all lean/non-obese NAFLD patients adjust their diet, exercise, and lose weight (weight loss to a reduction in visceral obesity or >5% of body weight).
It can also be done to improve insulin resistance (IR).
Purpose of dietary adjustments (such as adhere to the Mediterranean diet or consume more monounsaturated or polyunsaturated fatty acids, insoluble dietary fiber, and less sugary beverages) or drink coffee, but long-term studies are needed for non-obese NAFLD patients
.

There is currently no proven drug regimen for the treatment of non-obese NAFLD patients, and some potential drugs are still being tested in the future
.

Literature index: Ahadi M, Molooghi K, Masoudifar N, et al.
A review of non-alcoholic fatty liver disease in non-obese and lean individuals[J].
J Gastroenterol Hepatol.
2020 Nov 20.