Background
Non-alcoholic fatty liver disease (NAFLD), as the most common liver disease [
1,
2], occurs when fat is deposited (steatosis) in the liver without excessive alcohol use. The most extreme NAFLD form is non-alcoholic steatohepatitis (NASH) [
3]. NAFLD is related to insulin resistance and metabolic syndrome (obesity, combined hyperlipidemia, diabetes mellitus type 2, and high blood pressure). It may respond to treatments originally developed for other insulin-resistant conditions such as type 2 diabetes mellitus [
3,
4].
The global prevalence of NAFLD is emerging as 25.2% [
5]. However, up to 80% of obese people have NAFLD [
6‐
8]. The usual risk factors for NAFLD are obesity, impaired blood glucose regulation [
9,
10], dyslipidemia, and older age [
11,
12]. Inflammation and oxidative stress are the main inducers of insulin resistance that influence the pathology of NAFLD [
13,
14]. Insulin resistance has a direct association with liver fat content [
15].
Irisin, as a myokine [
16] and adipokine [
17], has a direct relationship with exercise and is related inversely to the triglyceride content of hepatocytes [
16]. Irisin can modify insulin sensitivity [
16,
18‐
21] by modulating glucose and lipid metabolism [
19,
22] and enhancing uncoupling protein-1 (UCP1) expression which stimulates thermogenesis [
19,
20,
23]. Regular exercise training and improving lifestyle [
18,
20,
21,
23,
24] improve secretion of irisin by increasing peroxisome proliferator-activated receptor gamma (PPAR-γ) coactivator 1-alpha (PGC-1α). PGC-1α is a transcriptional coactivator which regulates the genes involved in energy metabolism through interacting with the PPAR-γ [
25]., According to a study in obese NAFLD patients, liver enzymes and triglyceride contents had an inverse relationship with serum irisin [
26]. Thus, irisin may play an important role in the amelioration of hepatic diseases especially NAFLD [
16].
The dietary polyphenols as anti-oxidant and anti-inflammatory compounds have important roles [
27]. GC (
Elettaria cardamomum) from the ginger family as “the queen of spices” consists of numerous polyphenols such as quercetin [
28], which suppress nuclear factor-kappa B (NF-κB) [
28‐
31]. This factor is a protein complex involved in the control of cytokine production and cellular responses to stimuli such as inflammatory cytokines and oxidative stress [
32]. Some of the polyphenols such as quercetin and resveratrol can activate PGC-1α [
33,
34]. According to a study on adipocytes, quercetin increased the gene expression of irisin [
17]. So, GC may influence serum irisin, insulin resistance, and hepatic steatosis [
16].
Weight loss and physical activity are the common therapeutic approaches of NAFLD [
35,
36]. Due to the disputable treatment of NAFLD, new therapies may be necessary for the amelioration of NAFLD [
37]. Because of the challenge of weight loss and physical activity for a long time [
38], changing the dietary ingredients may be an effective approach [
39‐
41]. Important and different health effects have been reported for GC including antioxidant and anti-inflammatory effects [
42‐
44]. 1,8-cineole and alpha-terpinyl acetate are the two major components of cardamom volatile oil [
45].
Cardamom in many animal models has improved glucose metabolism [
46‐
48]. Nevertheless, similar human studies are very limited. In Only two distinct studies of GC supplementation, changes of FBS and insulin sensitivity in overweight or obese pre-diabetic women [
49,
50] and glycemic indices (FBS, insulin, and HbA1c) among type 2 diabetic patients [
51], were not significant. However, insulin sensitivity in pre-diabetic women revealed a significant improvement across the cardamom group [
49].
Due to the important effects of irisin in various metabolic pathways, its hepatic role should be studied. The stimulation of irisin secretion by GC in overweight or obese NAFLD patients should also be assessed. Meanwhile, the GC effects on serum irisin levels, glucose indices, and lipids in overweight or obese NAFLD patients have not previously been investigated. So, this study was planned to determine the efficacy of GC on serum irisin levels, glucose profiles, and lipids in these patients.
Discussion
This trial for the first time assessed the effects of GC on serum irisin level, glucose indices, and lipids among overweight or obese NAFLD patients. According to both unadjusted and adjusted analysis, in comparison with placebo, GC significantly augmented serum irisin, HDL-c, and QUICKI and reduced FBI, HOMA-IR, and TG levels. In addition, GC significantly lowered the grade of fatty liver. Furthermore, the decrease in LDL-c was significant in the unadjusted model and showed a trend in the adjusted model. Based on our previous findings in the other part of this trial [
59], compared with placebo, GC significantly diminished serum alanine transaminase (ALT) by 127% and heightened Sirtuin 1 (Sirt1) by 40% (
P < 0.05). In addition, the fall in BMI showed a trend among GC group in comparison with the placebo group. So, these improvements may explain the mechanism of GC effects on serum irisin, glucose indices, and lipids levels.
The results of different studies on the health effects of GC are controversial, with some of them presented further.
According to various animal studies, GC improved glycemic indices and lipids [
46‐
48,
60‐
66]. In two separate clinical trials of GC effect, changes in FBS and lipids (TC, TG, LDL-c, and HDL-c) in pre-diabetic women [
50] and changes in glycemic indices (FBS, insulin, and HbA1c) among type 2 diabetic patients [
51], were not significant. According to the second trial among type 2 diabetic patients, GC compared with placebo significantly reduced serum TC and LDL-c and elevated HDL-c levels [
51]. In addition, compared with placebo, changes in weight and BMI were not significant in both studies [
50,
67]. In another study on individuals with stage 1 hypertension, GC non-significantly lowered the lipids (TC, TG, LDL-c, and VLDL-c [very-low-density lipoprotein cholesterol]) [
43]. Further, Greater cardamom (
Amomum subulatum Roxb.) in patients with ischemic heart disease significantly improved atherogenic lipids (TC, TG, LDL-c, and VLDL-c) without significant changes in HDL-c. The possible reasons for the slight contrast are the difference in the design of the study, sample size, type of patients and supplement, duration of the intervention, the level of serum glucose indices at the baseline of study. Ginger, which is another member of the Zingiberaceae family, significantly improved FBS, TC, TG, and HDL-c levels according to a meta-analysis. The reported mechanisms were related to contents of phenols, polyphenols, and flavonoids, diminished synthesis, and increased excretion of cholesterol [
68].
The proposed various mechanisms of GC effect on glucose and lipid profiles include antioxidant capacity increment [
63,
64], inhibition of inflammation [
48], improvement of obesity, enhanced insulin activity and sensitivity (increased glycogenesis, decreased gluconeogenesis) [
62], increased expression and activity of PPARγ (improved glycemic control) [
46], and inhibition of cholesterol synthesis [
64]. The oxidative stress may damage tissue and impair insulin secretion and glucose transmission [
48]. Therefore, reducing oxidative stress can be effective in improving glucose metabolism. The hypolipidemic effect of GC may also improve plasma glucose and insulin levels and enhance insulin function [
60]. The effect of flavonoids on glycemic indices is related to reduced glucose absorption and enhanced glucose tolerance [
66].
Only in a cellular study on adipocytes, quercetin (as a standard flavonoid in GC) significantly amplified the expression of irisin [
17]. According to the beneficial effects of irisin on glucose indices and the increase of its serum levels with GC, this new mechanism in ameliorating glycemic status is suggested through increasing irisin levels.
In a study with three levels of GC on hepatotoxicity in albino mice, a significant reduction in weight gain was observed [
60]. These findings were attributed to the antioxidant capacity increment. In another study in male Wistar rats with metabolic syndrome, high levels of GC (3 g/kg body weight) augmented visceral obesity and total body fat [
69]. It may be attributed to the high dose of GC.
The probable mechanism for interpreting the effects of GC on weight and BMI involves reduction of visceral fats and the absorption of foods especially fats in the gastrointestinal system and possibly increased oxidation of fats by affecting the involved enzymes [
50]. In addition, these observed effects may be related to the contents of GC including phenols and flavonoids. The reported mechanisms of the effect of flavonoids on weight are the reduction of fat absorption by inhibiting pancreatic lipase [
70‐
72], enhanced expression of PPAR-α gene and carnitine palmitoyltransferase-1 (CPT-1), and diminished gene expression of enzymes involved in fat synthesis [
73]. Also, 1,8-cineole as a major component of the GC oil has significantly reduced fat mass in various studies [
69].
The novelty would make this study very relevant. As the side-effects of the GC (up to 3 g/day) had not been reported previously, it may be practically feasible for patients to continue taking it in the long run. Nevertheless, the effects and durability of this intervention in the long run should be investigated. The use of the GC in some diseases especially NAFLD needs to be further studied. In addition, the emergence of obesity and, consequently, NAFLD should also be considered.
The important strengths of this study were: the earliest assessment of GC effects in overweight or obese NAFLD patients, the double-blinded stratified blocked randomization design, recruiting the participants with newly diagnosed NAFLD without any treatment, and assessing dietary intakes and physical activity status and adjusting for them. However, some limitations were the self-reporting of diet and physical activity, no liver biopsy, measuring gamma-glutamyl transferase (GGT), hemoglobin A1c (HbA1c), body composition, and bioavailability and serum levels GC or its components, and determining the durability of the intervention in the long run, and 24-h food recall which is not appropriate for determining the usual food intake.