Skip to main content
PMC home page
Preventive Nutrition and Food Science logoLink to Preventive Nutrition and Food Science
. 2019 Dec 31;24(4):400–409. doi: 10.3746/pnf.2019.24.4.400

Beneficial Effects of Low-Calorie-Carbohydrate/High-Agar Diet on Cardiometabolic Disorders Associated with Non-Alcoholic Fatty Liver Disease in Obese Rats

Sabrine Louala 1, Myriem Lamri-Senhadji 1,✉
PMCID: PMC6941718  PMID: 31915635

Abstract

Energy restriction and low carbohydrate diets are recommended as nutrition therapies to prevent becoming overweight or obese. However, their beneficial effects in non-alcoholic fatty liver disease (NAFLD) are less well investigated. In addition, the effects of the type of polysaccharides incorporated into these diets and their contents have been scarcely studied. Therefore, this study aimed to elucidate whether low-calorie-carbohydrate high-agar diets could improve liver metabolic dysfunction, membrane fluidity, oxidative damage, and endothelial dysfunction in obese rats. Obesity was induced by feeding rats a high-fat diet (HFD) for 10 weeks. The obese rats were then divided into two homogenous groups: the first group was fed low-calorie-carbohydrate/high-agar diet (LCC/HA) and the second continued to consume the HFD for 4 weeks [obese control (Ob-C)]. Normo-ponderal rats were fed a normal diet during the entire study, and were used as the control (N-C). Compared with the Ob-C group, body weight, hepatic lipids, low density lipoproteins cholesterol (C), the non esterified cholesterol/phospholipids ratio, serum transaminases activities, and lipid peroxidation markers (thiobarbituric acid reactive substances and lipid hydroperoxides) were reduced in LCC/HA group (P<0.05). However, the serum concentration of high density lipoproteins-C was enhanced (P<0.05). In addition, we observed improved antioxidant defence and endothelial dysfunction associated with antioxidant enzymes, such as superoxide dismutase, glutathione peroxidase, and catalase (P<0.05), and nitric oxide level (P<0.05). These findings suggest that hypocaloric diets low in energy and carbohydrates and rich in agar may be beneficial against HFD-induced hepatic steatosis damage, and may be a promising therapeutic strategy to counteract NAFLD development associated with obesity.

Keywords: liver steatosis, low carbohydrate diet, agar, oxidative stress, nitric oxide

INTRODUCTION

Non-communicable diseases are the most prevalent cause of morbidity and mortality in the world (Mozaffarian, 2017), even in developing countries (Mensah et al., 2017). Non-alcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease worldwide, with prevalence reaching 25% in the global population (Araújo et al., 2018). Obesity, hyperlipidemia, diabetes mellitus, metabolic syndrome, and insulin resistance (IR) are well-known pathological features of NAFLD (Lonardo et al., 2015; Younossi, 2019). Hepatic abnormalities were characterized principally by triacylglycerol (TG) accumlation that induces liver fat (hepatic steatosis) (Nassir et al., 2015). Liver lipids storage results from an imbalance between lipid acquisition [from adipose tissue-derived fatty acids (FA) and de novo lipogenesis] and lipid clearance (TG-rich lipoprotein secretion) (Cohen et al., 2011; Gong et al., 2017). An increasing body of evidence shows that NAFLD is not only a potentially progressive liver disease, but also has systemic consequences. Among mechanisms linking cardiovascular disease (CVD) risk with hepatic steatosis, the most prominent factors appeared to be IR, low-grade chronic inflammation and hyperlipidemia (Bhatia et al., 2012; Nseir et al., 2011). Oxidative stress plays a key role in the initiation and progression of both NAFLD and CVD. An excessive production of reactive oxygen species (ROS) is responsible for low density lipoprotein (LDL) oxidation (Mangge et al., 2014), which may promote transformation of macrophages into foam cells; this represents the first step in the formation of atherosclerotic lesions. In many clinical studies, elevated systemic markers of oxidative stress, specifically lipid peroxidation, have been found in patients with NAFLD (Morita et al., 2012; Gaens et al., 2012).

The relationship between type of diet and NAFLD development is complex and extends beyond total energy intake. Low-calorie (LC) diets have been commonly recommended as nutrition therapy to prevent patients becoming overweight or obese, and protect against associated complications. Studies have shown potentially beneficial effects of LC diets (low in carbohydrate and rich in fiber) on obesity by suppressing the lipogenesis pathway in the liver and attenuating hepatic steatosis, inflammatory processes, and oxidative stress (Linden et al., 2016; Kim et al., 2016). Independently of high energy intake, the macronutrient composition of the diet, particularly consumption of carbohydrates (CHO), sugars, fats, and proteins, and low fiber intake may be associated with risk of NAFLD (Eslamparast et al., 2017). The low-CHO energy-restricted diets (<50 g/d and ≤45% of daily calorie intake) had become a strategy for management of weight and metabolic disorders. In this context, several studies have indicated that low-CHO diets may be effective in rapidly improving intrahepatic lipid levels and biochemical markers of liver function (Rodríguez-Hernández et al., 2011; Browning et al., 2011; Volynets et al., 2013). The existing literature do not describe the specific or simultaneous action of energy and nutrient intake, but just highlight foods and/or functional compounds with anti-obesity properties (Eslamparast et al., 2017).

Previous studies have suggested that high soluble fiber intake reduces body weight and is inversely correlated with LDL-cholesterol (LDL-C) level, hepatic lipid accumulation, plasma transaminases concentration, IR, and NAFLD fibrosis score (Chen et al., 2017; Krawczyk et al., 2018; Cantero et al., 2017). Agar-agar is the main component of the cell wall of marine red algae, and is widely used as functional food for reducing body weight (Hong et al., 2017). The health benefits of agar-agar are attributed to the antioxidant, anti-inflammatory, anti-diabetic, anti-obesity, and anti-atherogenic properties of soluble fiber (Maeda et al., 2005; Kim et al., 2008; Seo et al., 2012; Kang et al., 2016), which represents 80% of agar-agar. A recent study showed that agar extracted from Gelidium amansii is beneficial for reducing body weight, reducing amounts of adipose tissue, plasma total cholesterol (TC) and TG, reducing TG content in adipose tissue, and reducing hepatic lipid accumulation, by decreasing cholesterol absorption and increasing bile acid and fecal fat excretion in an animal model (Yang et al., 2017; Yang et al., 2019). However, studies examining the effects of diets low in energy and carbohydrate and high in agar on preventing NAFLD progression and obesity-associated CVD risk are missing. Therefore, the aim of this study was to investigate the effects of low-calorie-carbohydrate/ high-agar diet (LCC/HA) on overall liver function, including intrahepatic lipid and aminotransferases activities, membrane fluidity, oxidative stress, and nitric oxide (NO) bioavailability in the serum and tissues of obese rats.

MATERIALS AND METHODS

Animals and diets

Albinus male Wistar rats (Pasteur Institute, Algiers, Algeria) (n=18) aged four weeks old and weighing 63±5 g were used during this study. The animals were housed in standard environmental conditions (temperature 24°C, humidity 60%, and with a 12-h light/dark cycle) and had free access to food and water. The experimental protocol used was approved by the Institutional Animal Care and Use Committee at University Oran 1, Oran, Algeria (Approval no. PNR 047, LNCMW0911000). The ethical aspects were carefully followed according to the Council of European Communities (1986) general guidelines for the care and use of laboratory animals. In order to induce obesity, an experimental group (n=12) was received a high-fat diet (HFD) for ten weeks. After this period and at a body weight (BW) of 405±14 g, the obese rats were divided into two groups (n=6). The first group was fed a LCC/HA diet (277 kcal/100 g with 34% CHO and 31% agar) and the second continued to consume the HFD (456 kcal/100 g) for 28 days [obese control (Ob-C)]. The normo-ponderal rats (N-C group) (n=6) were fed with the normal diet (381 kcal/100 g) throughout the experiment.

Body weight and food consumption were recorded weekly and daily, respectively. Detailed compositions of all diets are shown in Table 1.

Table 1.

Composition of experimental and control diets

Ingredients LCC/HA HFD N-C
g/100 g Energy (%) g/100 g Energy (%) g/100 g Energy (%)
Casein 20 29 20 17 20 21
Corn starch 34 49 45 39 60 63
Sucrose 4 6 4 4 4 4
Sunflower oil 5 16 20 40 5 12
Agar agar 31 – 5 – 5 –
Mineral mix 4 – 4 – 4 –
Vitaminic mix 2 – 2 – 2 –
Total (kcal/100 g) 277 456 381
Open in a new tab

LCC/HA, low-calorie-carbohydrate/high-agar diet; HFD, high-fat diet; N-C, normal control diet.

Sample collection

On the 28th day of the experiment, after 12 h of fasting, six rats from each group were anesthetized with sodium pentobarbital (60 mg/kg BW) (French Pharmaceutical Cooperation, Melun, France). Blood was extracted from the abdominal aorta into dry test tubes and serum was prepared by low-speed centrifugation (1,000 g for 20 min at 4°C) (Sigma Laborzentrifugen GmbH, Osterode am Harz, Germany). Organs (liver, heart, and aorta) were removed, rinsed with cold saline solution (0.9% NaCl), and weighed. A serum aliquot was preserved in tubes containing 0.1% Na2ethylenediaminetetraacetic acid and 0.02% sodium azide for lipoprotein assays. Tissue samples were stored at −70°C until analysis.

Biochemical study

Lipid and lipoprotein content and transaminase activity analysis

The amount of total lipids (TL) in the liver was determined by a gravimetric method after lipid extraction (Folch et al., 1957). TG contents were estimated using an enzymatic colorimetric methods (kit CHOD-PAP; Biocon Diagnostik, Vöhl/Manenhagen, Germany). Serum and liver non-esterified cholesterol (NEC) concentrations were estimated using an enzymatic method (kit CHOD-PAP; Biolabo S.A.S., Maizy, France). Phospholipid (PL) levels were assessed by enzymatic determination of PLs (kit CHO-POD; Cypress Diagnostics, Langdorp, Belgium) in serum and liver. Non-esterified fatty acid (NEFA) contents were determined using enzymatic colorimetric assay kit (Sigma-Aldrich Co., St. Louis, MO, USA). The NEC/ PL ratio was calculated to estimate membrane fluidity. Lipoprotein fractions were separated using the precipitation method. Serum LDLs were isolated by precipitation (Burstein et al., 1970) using MgCl2 and phosphotung-state (Sigma-Aldrich Chimie S.a.r.l., Lyon, France). High density lipoprotein (HDL2 and HDL3) extractions were separated by precipitation (Burstein et al., 1989) using MgCl2 and dextran sulfate MW 500,000 Da (Sigma-Aldrich Chimie S.a.r.l.). The cholesterol in each fraction was determined by enzymatic colorimetric methods described previously. Serum aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT) activities were estimated using a colorimetric method (Chronolab Systems, S. L., Barcelona, Spain).

Lipid peroxidation analysis

Thiobarbituric acid reactive substances (TBARS) levels were measured using malondialdehyde (MDA) as a reference (Quintanilha et al., 1982; Ohkawa et al., 1979). In serum, lipid hydroperoxides (LOOH) concentrations were determined by ferric ions oxidation (Nourooz-Zadeh et al., 1996). In tissues, LOOH contents were determined according to the method of Eymard and Genot (2003). Serum IsoP (15-isoprostane F2t) levels were determined by the competitive enzyme immunoassay (EIA) method (Oxford Biomedical Research, Oxford, MI, USA).

Antioxidant enzymes activities measurement

The enzymatic activities of superoxide dismutase (SOD) (EC 1.15.1.1), glutathione peroxidase (GSH-Px) (EC 1.11.1.9), and glutathione reductase (GSSH-Red) (EC 1.6.4.2) were estimated using kits methods (Cayman Chemical, Ann Arbor, MI, USA). Catalase (CAT) (EC 1.11.1.6) activity was determined as described previously (Aebi, 1974).

NO bioavailability

Serum and tissue nitrite and nitrate levels were determined using the Griess reaction (Cortas and Wakid, 1990). NO has a half-life of only a few seconds because it is readily oxidized to nitrite (NO2−) and subsequently to nitrate (NO3−), which serve as index parameters for NO production.

Statistical analysis

Statistical analysis was carried out using STATISTICA (version 10, StatSoft Inc., Tulsa, OK, USA). Values were expressed as the mean±standard error of mean (SEM) for six rats per group. Data were analysis by analysis of variance (one-way ANOVA), and differences in the means were assessed using Duncan’s new multiple range tests (Duncan, 1955). The means with different letters were considered significantly different (P<0.05).

RESULTS AND DISCUSSION

Effects of LCC/HA on body and liver weight and energy intake

After four weeks of the nutritional experiment, the BW and liver weight of rats in the LCC/HA and Ob-C groups were reduced by a similar amount (−14%). However, the BW remained higher than the N-C group (+15%) (Table 2). The energy intake (kcal/rat/d) was reduced in the LCC/HA group compared with the Ob-C and N-C groups (−36% and −26%, respectively) (Table 2).

Table 2.

Body weight, liver weight, and food and energy intake

LCC/HA Ob-C N-C
Body weight (g) 376±22b 436±08a 326±13c
Weight gain (g) −1.07±0.25b 1.24±0.31a 1.58±0.92a
Food intake (g/rat/d) 24.10±0.46 23.32±0.80 24.01±0.56
Total calorie intake (kcal/rat/d) 66.52±1.80c 106.36±3.29a 91.22±2.35b
Liver weight (g) 7.98±0.66b 11.12±0.49a 7.95±0.60b
Open in a new tab

Data are shown as mean±SEM for six values per group.

After analysis of variance, classification of the means was performed using the Duncan’s multiple range test.

The means with different letters (a–c) are considered significantly different (P <0.05).

LCC/HA, low-calorie-carbohydrate/high-agar diet; Ob-C, obese control; N-C, normal control diet.

Changing eating habits (associated with physical activity) is the recommended cornerstone for weight loss. Low energy diets are the most efficient therapeutic target for NAFLD (Marchesini et al., 2016). In rodents, nutrients such as CHO and casein found in low energy diet are effective regulators that counteract obesogenic effects of high-fat diets (Marsset-Baglieri et al., 2004; Madsen et al., 2008). Variations in energy density and satiating quality of foods, and differing macronutrient composition may influence the potential of low-CHO diets for aiding weight loss (Juanola-Falgarona et al., 2014). Most low energy diets with low glycemic indexes have a high fiber content, which prolongs distension of the gastrointestinal tract, resulting in increased and prolonged secretion of cholecystokinin, ghrelin, glucagon, glucagon-like peptide 1, and glucose dependent insulinotropic peptide, all of which are considered satiety modulating factors (Radulian et al., 2009; Rebello et al., 2013; Juanola-Falgarona et al., 2014). In this study, the LCC/HA was characterized by a high fiber content (31%) and low in CHO (34%), compared with the control diets (high fat and normal diets) (Table 1). This difference in nutrient composition may be indicative of the effectiveness of the diets for weight loss. Evidence from animal and human studies suggest that the composition and function of the gut microbiota play critical roles in energy homeostasis and development of obesity (Khan et al., 2016), which may also explain the observed benefits of high-fiber carbohydrates, independent of total calorie intake. Several studies reported that dietary carbohydrates, especially those that are not digested in the upper part of the gut, can enhance growth and the functions of the gut microbiota community (Huaman et al., 2018). Increasing dietary fiber intake through specific prebiotics may stimulate satiety hormones and enhance appetite control, which can help aid body weight control (Parnell et al., 2012).

Liver weight was decreased for rats in the treated group compared with the Ob-C group. This reduction in weight may be due to a decrease in fat deposition (especially at the visceral level), probably by inhibition of lipogenesis, which may explain the weight loss in rats receiving with LCC/HA. Several studies have demonstrated that low-calorie- carbohydrate diets reduce liver weight through elevating catabolic processes with a concomitant decrease of insulin and/or glucose levels in hepatocytes (Moura et al., 2012; Margolis et al., 2016). In rats, lipogenesis in the liver is as important as in adipose tissue (Axen et al., 2013). The lower liver weight in rats fed the LCC/HA compared with the Ob-C was probably the result of a reduction in liver lipids, thus reducing hepatic steatosis induced by the HFD. It has been demonstrated that dietary fiber intake may reduce intestinal absorption of nutrients and increase the quantity of fat excreted in faeces (Harrat et al., 2019); this confirms the probable ability of agar to bind dietary fat, as recently hypothesized (Yang et al., 2019). These results suggest that diets low in energy and carbohydrates but rich in agar effectively increase the liver’s ability to excrete excess fat.

Effects of a LCC/HA on liver lipids profile

The LCC/HA reduced contents of TG, NEC, and NEFA hepatic lipid. The liver TL content was lowered by −13% in LCC/HA group compared with the Ob-C group. Similarly, lower amounts of TG (−51%), NEFA (−43%), and NEC (−17%) levels was recorded for the LCC/HA group compared with the Ob-C group (Table 3). In contrast, the liver PL concentration was higher in the LCC/HA group (+45%) (Table 3). The liver contents of TG and NEFA were 34% and 21% lower, respectively, for rats in the LCC/HA group compared with the N-C group, whereas the hepatic PL concentration was increased by 50% (Table 3).

Table 3.

Liver total lipids, lipid profile, lipoproteins-cholesterol contents, transaminases activities, and membrane fluidity

Parameters LCC/HA Ob-C N-C
Liver lipids amounts
 TL (mg/g) 173.16±0.64b 198.32±1.55a 166.81±2.16b
 TG (μmol/g) 27.90±0.58c 57.07±1.38a 42.40±1.89b
 NEC (μmol/g) 45.38±0.98b 54.49±0.67a 44.63±0.56b
 PL (μmol/g) 62.48±0.43a 43.01±0.50b 41.79±0.43c
 NEFA (μmol/g) 37.56±0.41b 65.64±0.56a 38.30±0.56b
Lipoprotein-cholesterol contents
 LDL-C (mmol/L) 0.50±0.01b 1.57±0.02a 0.54±0.02b
 HDL-C (mmol/L) 0.47±0.03a 0.30±0.02b 0.43±0.03a
Transaminases activities
 ALAT 15.46±0.42b 39.07±0.70a 14.91±0.70b
 ASAT 17.74±0.32c 37.63±0.83a 20.81±0.43b
Membrane fluidity
 NEC/PL 0.32±0.02b 1.62±0.10a 0.39±0.02b
Open in a new tab

Data are shown as the mean±SEM for six values per group.

After analysis of variance, the classification of the means was performed using the Duncan’s multiple range test.

The means with different letters (a–c) were considered significantly different (P <0.05).

LCC/HA, low-calorie-carbohydrate/high-agar diet; Ob-C, obese control; N-C, normal control diet; TL, total lipids; TG, triacylglycerols; NEC, non-esterified cholesterol; PL, phospholipids; NEFA, non esterified fatty acids; HDL-C, high density lipoprotein-cholesterol; LDL-C, low density lipoprotein-cholesterol; ALAT, serum alanine aminotransferase; ASAT, aspartate aminotransferase.

Exposure of the liver to high intakes of lipids may result in rapid stimulation of lipogenesis and TG accumulation, which may contribute to the reduction of insulin sensitivity and hepatic glucose intolerance (Bays et al., 2013). Several mechanisms may explain these effects, including reduction or inhibition of the activity of hydroxy methyl glutaryl CoA reductase (key enzyme in cholesterol biosynthesis) and stimulation of cholesterol 7 alpha hydroxylase activity (enzyme responsible for the conversion of cholesterol to bile acids). The LCC/HA contains 10-fold more fiber in the agar-agar form compared with the N-C group. Agar is a substance that consists of agarose (active compound of the agar-agar responsible for the gelling action) and agaro-pectin.

Agar has numerous functional properties. In addition to being a gelling product, agar saturates fat sensors. Currently, it is considered to be one of the best bioactive products for prevention and treatment of obesity (Mohamed et al., 2014). The low-calorie-carbohydrate diet used in the present study contained 31% agar fiber. Thus, one of the reasons why the LCC/HA can improve liver lipid metabolism may be related to its high levels of agar soluble fiber (80%).

Supplementation of agar extract (3%) in the diets of HFD-induced obese hamsters for 9 weeks induced reductions in body and adipose tissue weights, decreases in plasma TC/TG levels, hepatic TC/TG accumulation and adipose TG contents, and increases in fecal TC/TG contents and adipose tissue lipolysis. The authors suggested that agar extracts down-regulate hepatic lipid metabolism through phosphorylating adenosine monophosphateactivated protein kinases, up-regulating peroxisome proliferator activated receptor-α, and upregulating uncoupling protein-2 in HFD-induced obese hamsters; this subsequently increases fatty acid β-oxidation in the liver (Yang et al., 2019).

Further, LC diets improve lipid profiles via mechanisms such as increasing β-oxidation of FA and/or decreasing de novo lipogenesis in the liver (Baumeier et al., 2015). In addition, consumption of a low-CHO diet (<20 g/d) for 2 weeks may effectively alleviate metabolic abnormalities, by decreasing the accumulation of hepatic TGs and reducing development of hepatic steatosis (Browning et al., 2011). These findings suggest that diets low in energy and carbohydrates and rich in agar are beneficial for reducing lipid accumulation in the liver of obese rats, and for improving lipid metabolism. It is possible that the high dietary fiber content in the form of agar plays an important role in determining the effectiveness of low-energy-carbohydrates for preventing progression of NAFLD in obese rats.

Effects of LCC/HA on serum transaminases activities

Serum ALAT and ASAT activities were decreased by 60% and 53%, respectively, in LCC/HA group compared with the Ob-C group. Further, ALAT activity was similar between rats in the N-C and LCC/HA groups, whereas the ASAT level was lowered by −15% (Table 3).

Findings from the present study indicate that consumption of a LCC/HA reduces serum concentrations of liver transaminases. Rodríguez-Hernández et al. (2011) showed that weight reduction improves serum levels of aminotransferase irrespective of dietary macronutrient composition (low-CHO diet or low-fat diet). Other investigators have shown that beside weight reduction, low-CHO diets had a greater number of beneficial effects for treatment of patients with NAFLD compared with high carbohydrate diets (de Luis et al., 2010; Browning et al., 2011). Another determinant for the change in liver enzymes may be related to hepatic fat content since some investigators have reported that lower ALAT and ASAT levels in patients with NAFLD improve liver histology (Jang et al., 2018). Other possible reason for the variation in transaminase responses may be related to the increased amounts of dietary agar fiber in the LCC/HA. Increased soluble dietary fiber can positively affect NAFLD, and decrease serum ALAT and ASAT levels (Parnell et al., 2012). Previous study have shown that agar protects against liver damage in rats by efficiently inhibiting malondialdehyde formation and decreasing ASAT and ALAT levels (Chen et al., 2006). This study confirms that LCC/ HA possesses hepatoprotective potential against HFD-induced hepatic steatosis damage.

Effects of LCC/HA on HDL-C, LDL-C, and membrane fluidity

LDL-C was reduced 68% and HDL-C was increased 57% in LCC/HA group compared with the Ob-C group (Table 3). These values were comparable with those reported for rats in the N-C group.

For rats in the LCC/HA group, the NEC/PL ratio was decreased 5-fold compared with rats in the Ob-C group, however the ratio did not significantly differ from that reported for the N-C group (Table 3).

The increase in HDL-C and decrease in LDL-C in rats receiving the LCC/HA are consistent with favoring a cardio- protective effect. The improvement in HDL-C observed in the treated rats is probably a consequence of an increase in expression of adiponectin owing to its anti-atherogenic effects (Ruan and Dong, 2016). Our results are agreement with a previous study (Chen et al., 2015) which showed that hypocaloric-low-CHO diets (containing 34% carbohydrates) regulate serum lipoprotein concentrations (LDL-C and HDL-C), and are associated with production of plasma apolipoprotein A-1. The low LDL-C levels observed following consumption of the LCC/HA may also result from a reduction of cholesterol at the level of the mitochondrial membrane (Harmancey et al., 2010), a potent modulator of membrane fluidity. Previous studies have reported that membrane fluidity of rats fed a HFD is altered by changes in the content of hepatic cholesterol and phospholipids (Tanaka et al., 1989; Ciapaite et al., 2011). Our findings are agreement with these studies. Consumption of a LCC/HA has been previously shown to decrease NEFA concentrations (indicative of oxidation), probably due to changes in the fat composition of liver mitochondria and impaired oxidative phosphorylation (Vial et al., 2011). Therefore, the reduction of liver lipid accumulation observed for the LCC/HA group may be explained by an increase in adiponectin owing to liver lipid infiltration having favourable action on mitochondria membranes.

Effects of LCC/HA on prooxidant markers and antioxidant enzymes activities

Serum TBARS levels were decreased (1.8-fold) in rats fed the LCC/HA compared with the Ob-C. Similarly, serum LOOH was similar between the LCC/HA and N-C groups, but was reduced 1.8-fold in the LCC/HA group compared with the Ob-C group (Table 4). Serum IsoP concentrations were 2.7- and 1.9-fold lower in the LCC/HA group compared with the Ob-C and N-C groups, respectively (Table 4). Reductions in TBARS concentrations were recorded in the livers (−30%), hearts (−54%) and aortas (−56%) of rats fed the LCC/HA compared with the Ob-C (Table 4). However, TBARS were increased 11% in the LCC/HA group compared with the N-C group in liver, and was decreased 11% in heart and 38% in the aorta (Table 4). Similarly, decreases in LOOH levels were noted in the liver (2.1-fold), heart (2-fold) and aorta (3.3-fold) of the LCC/HA group compared with the Ob-C group (Table 4); however, compared with the N-C group, LOOH levels was higher in liver (1.1-fold higher) but lower in heart (1.7-fold) and aorta (2.2-fold).

Table 4.

Prooxydants biomarkers in serum and tissues

Groups LCC/HA Ob-C N-C
Serum
 TBARS (nmol Eq MDA/L) 30.01±2.65b 55.95±1.59a 29.45±0.73b
 LOOH (nmol Eq CUOOH/L) 56.84±7.06b 105.29±2.43a 51.86±1.47b
 IsoP (ng/L) 253.58±15.16c 680.41±71.67a 477.51±28.55b
Tissues
 Liver
  TBARS (nmol Eq MDA/g) 460.23±4.07b 653.66±18.63a 416.10±15.58c
  LOOH (nmol Eq CUOOH/g) 350.85±8.45b 751.78±13.31a 319.86±12.52c
 Heart
  TBARS (nmol Eq MDA/g) 217.98±39.47b 475.73±14.18a 246.15±15.45b
  LOOH (nmol Eq CUOOH/g) 262.11±58.05c 522.68±48.87a 449.91±26.62b
 Aorta
  TBARS(nmol Eq MDA/g) 249.44±25.86c 569.62±52.42a 402.96±31.08b
  LOOH (nmol Eq CUOOH/g) 117.98±17.83c 390.75±25.37a 263.05±14.18b
Open in a new tab

Data are shown as the mean±SEM for six values per group.

After analysis of variance, the classification of the means was performed using the Duncan’s multiple range test.

The means with different letters (a–c) were considered significantly different (P <0.05).

LCC/HA, low-calorie-carbohydrate/high-agar diet; Ob-C, obese control; N-C, normal control diet; TBARS, thiobarbituric acid reactive substances; LOOH, hydroperoxides; IsoP, isoprostanes.

In serum, rats fed the LCC/HA showed increases in SOD (1.8-fold), CAT (5.4-fold), GSH-Px (1.1-fold), and GSSH-Red (1.3-fold) activities compared with rats in the Ob-C group (Table 5). Further, SOD, serum GSSH-Red, and CAT activities were 1.4-, 1.2-, and 1.3-fold higher, respectively, in the LCC/HA group compared with the N-C group (Table 5).

Table 5.

Antioxidant enzyme activities in serum and tissues

Groups LCC/HA Ob-C N-C
Serum
 SOD (U/mL) 248.34±7.62a 139.11±6.93c 177.80±3.46b
 GSH-Px (nmol/min/mL) 90.14±0.00a 82.77±1.81b 90.42±1.79a
 GSSH-Red (nmol/min/mL) 132.44±7.20a 99.33±3.60b 113.34±1.80b
 CAT (U/min/mL) 62.47±0.72a 11.57±0.68c 48.07±1.03bs
Tissues
 Liver
  SOD (U/g) 25.64±1.93a 8.56±1.14d 16.82±0.54c
  CAT (U/min/g) 15.11±0.42a 8.35±0.02d 13.39±0.37b
  GSH-Px (nmol/min/g) 177.01±9,00a 123.53±9.00c 169.37±1.80ab
  GSSH-Red (nmol/min/g) 160.46±3.60a 115.88±1.80c 138.81±1.80b
 Heart
  SOD (U/g) 26.02±0.30a 19.76±0.60d 23.77±0.48b
  CAT (U/min/g) 13.02±0.13a 8.47±0.36c 13.53±1.19a
  GSH-Px (nmol/min/g) 202.48±5.40a 145.17±3.60d 192.29±1.80a
  GSSH-Red (nmol/min/g) 276.34±1.80a 225.40±5.40c 268.70±1.80a
 Aorta
  SOD (U/g) 23.43±0.48a 15.16±0.48d 20.19±0.12b
  CAT (U/min/g) 12.79±1.01a 7.59±0.23c 12.48±0.76a
  GSH-Px (nmol/min/g) 163.00±3.60a 148.99±1.80b 162.73±1.80a
  GSSH-Red (nmol/min/g) 216.49±3.60a 90.42±1.80c 182.10±5.40b
Open in a new tab

Data are shown as the mean±SEM for six values per group.

After analysis of variance, the classification of the means was performed using the Duncan’s multiple range test.

The means with different letters (a–c) were considered significantly different (P <0.05).

LCC/HA, low-calorie-carbohydrate/high-agar diet; Ob-C, obese control; N-C, normal control diet; SOD, superoxide dismutase; CAT, catalase; GSH-Px, glutathione peroxidase; GSSH-Red, glutathione reductase.

For all organ tissues analyzed, SOD activity was increased for rats in the LCC/HA group compared with the Ob-C group (P<0.05). In addition, compared with the N-C group, SOD activity in the LCC/HA group was higher in the liver, heart, and aorta (+52%, +9%, and +16%), respectively (Table 5). Further, increases in CAT activity was noted in the liver (1.8-fold), heart (1.5-fold), and aorta (1.7-fold) in the LCC/HA group compared with the Ob-C group (Table 5).

LCC/HA treatment significantly enhanced the activity of GSH-Px in the liver and heart (both 1.4-fold) (Table 5). In addition, increases in GSSH-Red activity was recorded in most tissues (1.4-fold in liver, 1.2-fold in heart, and 2.4-fold in aorta) in the LCC/HA group compared with the Ob-C group; however, compared with the N-C group, GSSH-Red activity was only higher in the liver and aorta (both 1.2-fold) (Table 5).

These results show that the LCC/HA may protect serum and tissues against the cytotoxic action and oxidative stress of HFDs. Our results clearly show a decrease in lipid peroxidation markers (TBARS, LOOHs, and IsoP levels) for rats receiving the LCC/HA; efficient antioxidant enzymatic defense may be linked to the decrease in lipids levels. It is well known that generation of free radicals is positively correlated with liver lipid concentrations (Volek et al., 2009). The reduction in lipid peroxidation may be the result of significant modifications to the cellular redox status in favor of antioxidants, associated with the reduction of hepatic lipids accumulation. In addition, assessment of antioxidant defense at the tissue level shows a high activity of tissue antioxidant enzymes (SOD, CAT, GSH-Px, and GSSH-Red) in obese rats receiving the LCC/HA, which may contribute to better anti-radical protection. However, increased GSH-Px activity at the hepatic and cardiac level could indicate an elevation of glutathione production since the latter is the specific substrate of this enzyme. The LCC/HA maintained the pro/antioxidant balance of cells and tissues by reducing their exposure to oxidative damage caused by the HFD. This work shows that a low calorie, LCC/HA decreases the occurrence of lesions related to oxidative aggression by reducing production of free radicals and lipid peroxides in the liver, and by increasing antioxidant enzymatic defense. This could probably be the result of reduced accumulation of lipids in the liver. Agar has been shown to enhance the activities of antioxidant enzymes, including SOD and GSH-Px (Chen et al., 2006). Agar had been indicated to improve hepatoprotective effects (Alam et al., 2017). Antioxidant enzymes such as SOD and GSH-Px are considered a primary defense system against oxidative damage; agar exerts antioxidant activity through both its own radical scavenging activity and by boosting the host’s antioxidant enzyme system (Chen et al., 2006). Therefore, our findings suggest that high content of agar in diets (in the context of energy restriction) can exert a hepatoprotective effect through scavenging ROS to prevent oxidative damage.

Effects of LCC/HA on NO bioavailability

NO level was elevated 1.9-fold in the LCC/HA group compared with the Ob-C group, but was comparable to that of the N-C group (Table 6). In tissues, NO concentrations were higher in liver (1.6-fold), heart (3.4-fold), and aorta (3.6-fold) in rats fed the LCC/HA compared with the Ob-C. In contrast, compared with the N-C group, NO levels were decreased in liver (1.6-fold) and aorta (1.3-fold), and enhanced in heart (1.6-fold) of rats in the LCC/HA group (Table 6).

Table 6.

Nitric oxide (NO) bioavailability in serum and tissues

Groups LCC/HA Ob-C N-C
NO-serum (μmol/L) 2.42±0.09a 1.27±0.08b 2.46±0.03a
NO-tissues (μmol/g)
 Liver 3.03±0.14b 1.86±0.06c 4.68±0.06a
 Heart 5.53±0.26a 1.61±0.56c 3.51±0.78b
 Aorta 4.33±0.72b 1.18±0.10c 5.73±0.71a
Open in a new tab

Data are shown as the mean±SEM for six values per group.

After analysis of variance, the classification of the means was performed using the Duncan’s multiple range test.

The means with different superscripts were considered significantly different (P <0.05).

LCC/HA, low-calorie-carbohydrate/high-agar diet; Ob-C, obese control; N-C, normal control diet.

In the present study, the LC diet improved bioavailability of NO in rats with hepatic steatosis. The LC diet could have a protective effect against endothelial dysfunction (Chou et al., 2010; Donato et al., 2013) through underlying mechanisms such as by increasing bioavailability of NO (through enhancing expression and/or eNOS activity (Blanquicett et al., 2007), suppressing vascular oxidative stress associated with superoxide anion (O2•−) production, and attenuating lipid peroxidation (Chou et al., 2010; Donato et al., 2013). Animal experiments and clinical studies have shown that abnormal production of NO and elevated concentrations of endotheline-1 (ET-1) may be important contributors to endothelial dysfunction development, an early step in development of atherosclerosis in obesity (Weil et al., 2011; Sánchez et al., 2014). Soluble fiber can reduce CVD risk by its ability to regulate lipid metabolism, via reducing blood pressure, decreasing proinflammatory mediators, improving oxidative stress, and reducing endothelial dysfunction (Behall et al., 2006; Qi et al., 2006; Brock et al., 2006). However, the mechanism responsible for the protective effect of fiber on endothelial dysfunction is not well described. Dietary soluble fiber may stimulate NO generation and reduce ET-1 level (Xiao et al., 2009). In this study, it is possible that the protective effects of agar fiber on the vascular endothelium may be related to an improvement in NO production and/or a reduction in ET-1 concentration. Further research is needed to address these points.

This study shows that the LCC/HA exerts several mechanisms of action to improve HFD-induced hepatic steatosis damage, probably due to their specific or interactive actions. The LCC/HA attenuate cardiometabolic disorders associated with NAFLD in obese rats by reducing the BW and the weight of the liver, hepatic lipid accumulation, transaminases content, and by improving membrane fluidity, the pro/antioxidant balance and endothelial dysfunction.

The present study provides substantial evidence for the beneficial effect of this type of hypocaloric diet against HFD-induced hepatic steatosis damage and suggests it might be a promising therapeutic strategy to counteract NAFLD development associated with obesity.

ACKNOWLEDGEMENTS

This work was funded by the Ministry of Higher Education and Scientific Research-Algeria (PNR number 047).

Footnotes

AUTHOR DISCLOSURE STATEMENT

The authors declare no conflict of interest.

REFERENCES

  1. Aebi H. Catalase. In: Bergmeyer HU, editor. Methods of Enzymatic Analysis. 2nd ed. Vol. 2. Academic Press; Cambridge, MA. USA: 1974. pp. 673–684. [DOI] [Google Scholar]
  2. Alam J, Mujahid M, Badruddeen, Jahan Y, Bagga P, Rahman MA. Hepatoprotective potential of ethanolic extract of Aquilaria agallocha leaves against paracetamol induced hepatotoxicity in SD rats. J Tradit Complement Med. 2017;7:9–13. doi: 10.1016/j.jtcme.2015.12.006. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Araújo AR, Rosso N, Bedogni G, Tiribelli C, Bellentani S. Global epidemiology of non-alcoholic fatty liver disease/non-alcoholic steatohepatitis: what we need in the future. Liver Int. 2018;38:47–51. doi: 10.1111/liv.13643. [DOI] [PubMed] [Google Scholar]
  4. Axen K, Harper MA, Kuo YF, Axen K. Short-term high-fat diet impairs regulation of hepatic lipogenesis in rats. FASEB J. 2013;27:857.4–857.4. [Google Scholar]
  5. Baumeier C, Kaiser D, Heeren J, Scheja L, John C, Weise C, et al. Caloric restriction and intermittent fasting alter hepatic lipid droplet proteome and diacylglycerol species and prevent diabetes in NZO mice. Biochim Biophys Acta. 2015;851:566–576. doi: 10.1016/j.bbalip.2015.01.013. [DOI] [PubMed] [Google Scholar]
  6. Bays HE, Toth PP, Kris-Etherton PM, Abate N, Aronne LJ, Brown WV, et al. Obesity, adiposity, and dyslipidemia: a consensus statement from the National Lipid Association. J Clin Lipidol. 2013;7:304–383. doi: 10.1016/j.jacl.2013.04.001. [DOI] [PubMed] [Google Scholar]
  7. Behall KM, Scholfield DJ, Hallfrisch J. Whole-grain diets reduce blood pressure in mildly hypercholesterolemic men and women. J Am Diet Assoc. 2006;106:1445–1449. doi: 10.1016/j.jada.2006.06.010. [DOI] [PubMed] [Google Scholar]
  8. Bhatia LS, Curzen NP, Calder PC, Byrne CD. Non-alcoholic fatty liver disease: a new and important cardiovascular risk factor? Eur Heart J. 2012;33:1190–1200. doi: 10.1093/eurheartj/ehr453. [DOI] [PubMed] [Google Scholar]
  9. Blanquicett C, Graves A, Kleinhenz DJ, Hart CM. Attenuation of signaling and nitric oxide production following prolonged leptin exposure in human aortic endothelial cells. Investig Med. 2007;55:368–377. doi: 10.2310/6650.2007.00017. [DOI] [PubMed] [Google Scholar]
  10. Brock DW, Davis CK, Irving BA, Rodriguez J, Barrett EJ, Weltman A, et al. A high-carbohydrate, high-fiber meal improves endothelial function in adults with the metabolic syndrome. Diabetes Care. 2006;29:2313–2315. doi: 10.2337/dc06-0917. [DOI] [PubMed] [Google Scholar]
  11. Browning JD, Baker JA, Rogers T, Davis J, Satapati S, Burgess SC. Short-term weight loss and hepatic triglyceride reduction: evidence of a metabolic advantage with dietary carbohydrate restriction. Am J Clin Nutr. 2011;93:1048–1052. doi: 10.3945/ajcn.110.007674. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Burstein M, Fine A, Atger V, Wirbel E, Girard-Globa A. Rapid method for the isolation of two purified subfractions of high density lipoproteins by differential dextran sulfate-magnesium chloride precipitation. Biochimie. 1989;71:741–746. doi: 10.1016/0300-9084(89)90090-4. [DOI] [PubMed] [Google Scholar]
  13. Burstein M, Scholnick HR, Morfin R. Rapid method for the isolation of lipoproteins from human serum by precipitation with polyanions. J Lipid Res. 1970;11:583–595. [PubMed] [Google Scholar]
  14. Cantero I, Abete I, Monreal JI, Martinez JA, Zulet MA. Fruit fiber consumption specifically improves liver health status in obese subjects under energy restriction. Nutrients. 2017;9:E667. doi: 10.3390/nu9070667. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Chen H, Yan X, Zhu P, Lin J. Antioxidant activity and hepatoprotective potential of agaro-oligosaccharides in vitro and in vivo. Nutr J. 2006;5:31. doi: 10.1186/1475-2891-5-31. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Chen JH, Ouyang C, Ding Q, Song J, Cao W, Mao L. A moderate low-carbohydrate low-calorie diet improves lipid profile, insulin sensitivity and adiponectin expression in rats. Nutrients. 2015;7:4724–4738. doi: 10.3390/nu7064724. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Chen JP, Chen GC, Wang XP, Qin L, Bai Y. Dietary fiber and metabolic syndrome: a meta-analysis and review of related mechanisms. Nutrients. 2017;10:E24. doi: 10.3390/nu10010024. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Chou SH, Lee YC, Huang CF, Wang YR, Yu HP, Lau YT. Gender-specific effects of caloric restriction on the balance of vascular nitric oxide and superoxide radical. Cardiovasc Res. 2010;87:751–759. doi: 10.1093/cvr/cvq095. [DOI] [PubMed] [Google Scholar]
  19. Ciapaite J, van den Broek NM, Te Brinke H, Nicolay K, Jeneson JA, Houten SM, et al. Differential effects of short- and long-term high-fat diet feeding on hepatic fatty acid metabolism in rats. Biochim Biophys Acta. 2011;1811:441–451. doi: 10.1016/j.bbalip.2011.05.005. [DOI] [PubMed] [Google Scholar]
  20. Cohen JC, Horton JD, Hobbs HH. Human fatty liver disease: old questions and new insights. Science. 2011;332:1519–1523. doi: 10.1126/science.1204265. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Cortas NK, Wakid NW. Determination of inorganic nitrate in serum and urine by a kinetic cadmium-reduction method. Clin Chem. 1990;36:1440–1443. [PubMed] [Google Scholar]
  22. Council of European Communities. Council instructions about the protection of living animals used in scientific investigations (86/609/EEC) Off J Eur Communities. 1986:1–28. [Google Scholar]
  23. de Luis DA, Aller R, Izaola O, Gonzalez Sagrado M, Conde R. Effect of two different hypocaloric diets in transaminases and insulin resistance in nonalcoholic fatty liver disease and obese patients. Nutr Hosp. 2010;25:730–735. [PubMed] [Google Scholar]
  24. Donato AJ, Walker AE, Magerko KA, Bramwell RC, Black AD, Henson GD, et al. 2013. Life-long caloric restriction reduces oxidative stress and preserves nitric oxide bioavailability and function in arteries of old mice. Aging Cell. 2013;12:772–783. doi: 10.1111/acel.12103. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Duncan DB. Multiple range and multiple F tests. Biometrics. 1955;11:1–42. doi: 10.2307/3001478. [DOI] [Google Scholar]
  26. Eslamparast T, Tandon P, Raman M. Dietary composition independent of weight loss in the management of non-alcoholic fatty liver disease. Nutrients. 2017;9:E800. doi: 10.3390/nu9080800. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Eymard S, Genot C. A modified xylenol orange method to evaluate formation of lipid hydroperoxides during storage and processing of small pelagic fish. Eur J Lipid Sci Technol. 2003;105:497–501. doi: 10.1002/ejlt.200300768. [DOI] [Google Scholar]
  28. Folch J, Lees M, Sloane Stanley GH. A simple method for the isolation and purification of total lipides from animal tissues. J Biol Chem. 1957;226:497–509. [PubMed] [Google Scholar]
  29. Gaens KH, Niessen PM, Rensen SS, Buurman WA, Greve JW, Driessen A, et al. Endogenous formation of Nɛ-(carboxymethyl) lysine is increased in fatty livers and induces inflammatory markers in an in vitro model of hepatic steatosis. J Hepatol. 2012;56:647–655. doi: 10.1016/j.jhep.2011.07.028. [DOI] [PubMed] [Google Scholar]
  30. Gong Z, Tas E, Yakar S, Muzumdar R. Hepatic lipid metabolism and non-alcoholic fatty liver disease in aging. Mol Cell Endocrinol. 2017;455:115–130. doi: 10.1016/j.mce.2016.12.022. [DOI] [PubMed] [Google Scholar]
  31. Harmancey R, Wilson CR, Wright NR, Taegtmeyer H. Western diet changes cardiac acyl-CoA composition in obese rats: a potential role for hepatic lipogenesis. J Lipid Res. 2010;51:1380–1393. doi: 10.1194/jlr.M001230. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Harrat NI, Louala S, Bensalah F, Affane F, Chekkal H, Lamri-Senhadji M. Anti-hypertensive, anti-diabetic, hypocholesterolemic and antioxidant properties of prickly pear nopalitos in type 2 diabetic rats fed a high-fat diet. Nutr Food Sci. 2018;49:476–490. doi: 10.1108/NFS-06-2018-0169. [DOI] [Google Scholar]
  33. Hong SJ, Lee JH, Kim EJ, Yang HJ, Park JS, Hong SK. Anti-obesity and anti-diabetic effect of neoagarooligosaccharides on high-fat diet-induced obesity in mice. Mar Drugs. 2017;15:E90. doi: 10.3390/md15040090. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Huaman JW, Mego M, Manichanh C, Cañellas N, Cañueto D, Segurola H, et al. Effects of prebiotics vs a diet low in FODMAPs in patients with functional gut disorders. Gastroenterology. 2018;155:1004–1007. doi: 10.1053/j.gastro.2018.06.045. [DOI] [PubMed] [Google Scholar]
  35. Jang EC, Jun DW, Lee SM, Cho YK, Ahn SB. Comparison of efficacy of low-carbohydrate and low-fat diet education programs in non-alcoholic fatty liver disease: a randomized controlled study. Hepatol Res. 2018;48:E22–E29. doi: 10.1111/hepr.12918. [DOI] [PubMed] [Google Scholar]
  36. Juanola-Falgarona M, Salas-Salvadó J, Ibarrola-Jurado N, Rabassa-Soler A, Díaz-López A, Guasch-Ferré M, et al. Effect of the glycemic index of the diet on weight loss, modulation of satiety, inflammation, and other metabolic risk factors: a randomized controlled trial. Am J Clin Nutr. 2014;100:27–35. doi: 10.3945/ajcn.113.081216. [DOI] [PubMed] [Google Scholar]
  37. Kang MC, Kang N, Kim SY, Lima IS, Ko SC, Kim YT, et al. Popular edible seaweed, Gelidium amansii prevents against diet-induced obesity. Food Chem Toxicol. 2016;90:181–187. doi: 10.1016/j.fct.2016.02.014. [DOI] [PubMed] [Google Scholar]
  38. Khan MJ, Gerasimidis K, Edwards CA, Shaikh MG. Role of gut microbiota in the aetiology of obesity: proposed mechanisms and review of the literature. J Obes. 2016;2016 doi: 10.1155/2016/7353642. 7353642. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Kim KE, Jung Y, Min S, Nam M, Heo RW, Jeon BT, et al. Caloric restriction of db/db mice reverts hepatic steatosis and body weight with divergent hepatic metabolism. Sci Rep. 2016;6:30111–30125. doi: 10.1038/srep30111. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Kim MS, Kim JY, Choi WH, Lee SS. Effects of seaweed supplementation on blood glucose concentration, lipid profile, and antioxidant enzyme activities in patients with type 2 diabetes mellitus. Nutr Res Pract. 2008;2:62–67. doi: 10.4162/nrp.2008.2.2.62. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Krawczyk M, Maciejewska D, Ryterska K, Czerwińka-Rogowska M, Jamioł-Milc D, Skonieczna-Żydecka K, et al. Gut permeability might be improved by dietary fiber in individuals with non-alcoholic fatty liver disease (NAFLD) undergoing weight reduction. Nutrients. 2018;10:E1793. doi: 10.3390/nu10111793. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Linden MA, Fletcher JA, Meers GM, Thyfault JP, Laughlin MH, Rector RS. A return to ad libitum feeding following caloric restriction promotes hepatic steatosis in hyperphagic OLETF rats. Am J Physiol Gastrointest Liver Physiol. 2016;311:G387–G395. doi: 10.1152/ajpgi.00089.2016. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Lonardo A, Ballestri S, Marchesini G, Angulo P, Loria P. Nonalcoholic fatty liver disease: a precursor of the metabolic syndrome. Dig Liver Dis. 2015;47:181–190. doi: 10.1016/j.dld.2014.09.020. [DOI] [PubMed] [Google Scholar]
  44. Madsen L, Pedersen LM, Liaset B, Ma T, Petersen RK, van den Berg S, et al. cAMP-dependent signaling regulates the adipogenic effect of n-6 polyunsaturated fatty acids. J Biol Chem. 2008;283:7196–7205. doi: 10.1074/jbc.M707775200. [DOI] [PubMed] [Google Scholar]
  45. Maeda H, Yamamoto R, Hirao K, Tochikubo O. Effects of agar (kanten) diet on obese patients with impaired glucose tolerance and type 2 diabetes. Diabetes Obes Metab. 2005;7:40–46. doi: 10.1111/j.1463-1326.2004.00370.x. [DOI] [PubMed] [Google Scholar]
  46. Mangge H, Becker K, Fuchs D, Gostner JM. Antioxidants, inflammation and cardiovascular disease. World J Cardiol. 2014;6:462–477. doi: 10.4330/wjc.v6.i6.462. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Marchesini G, Petta S, Dalle Grave R. Diet, weight loss, and liver health in nonalcoholic fatty liver disease: pathophysiology, evidence, and practice. Hepatology. 2016;63:2032–2043. doi: 10.1002/hep.28392. [DOI] [PubMed] [Google Scholar]
  48. Margolis LM, Rivas DA, Ezzyat Y, Gaffney-Stomberg E, Young AJ, McClung JP, et al. Calorie restricted high protein diets down-regulate lipogenesis and lower intrahepatic triglyceride concentrations in male rats. Nutrients. 2016;8:E571. doi: 10.3390/nu8090571. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Marsset-Baglieri A, Fromentin G, Tomé D, Bensaid A, Makkarios L, Even PC. Increasing the protein content in a carbohydrate-free diet enhances fat loss during 35% but not 75% energy restriction in rats. J Nutr. 2004;134:2646–2652. doi: 10.1093/jn/134.10.2646. [DOI] [PubMed] [Google Scholar]
  50. Mensah GA, Wei GS, Sorlie PD, Fine LJ, Rosenberg Y, Kaufmann PG, et al. Decline in cardiovascular mortality: possible causes and implications. CircRes. 2017;120:366–380. doi: 10.1161/CIRCRESAHA.116.309115. [DOI] [PMC free article] [PubMed] [Google Scholar]
  51. Mohamed GA, Ibrahim Sabrin RM, Elkhayat ES, El Dine RS. Natural anti-obesity agents. Bulls Fac Pharm Cairo Univ. 2014;52:269–284. doi: 10.1016/j.bfopcu.2014.05.001. [DOI] [Google Scholar]
  52. Morita M, Ishida N, Uchiyama K, Yamaguchi K, Itoh Y, Shichiri M, et al. Fatty liver induced by free radicals and lipid peroxidation. Free Radic Res. 2012;46:758–765. doi: 10.3109/10715762.2012.677840. [DOI] [PubMed] [Google Scholar]
  53. Moura LP, Figueredo GA, Bertolini NO, Ceccato M, Pereira JR, Sponton AC, et al. Dietary restriction, caloric value and the accumulation of hepatic fat. Lipids Health Dis. 2012;11:2. doi: 10.1186/1476-511X-11-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  54. Mozaffarian D. Global scourge of cardiovascular disease: time for health care systems reform and precision population health. J Am Coll Cardiol. 2017;70:26–28. doi: 10.1016/j.jacc.2017.05.007. [DOI] [PubMed] [Google Scholar]
  55. Nassir F, Rector RS, Hammoud GM, Ibdah JA. Pathogenesis and prevention of hepatic steatosis. Gastroenterol Hepatol. 2015;11:167–175. [PMC free article] [PubMed] [Google Scholar]
  56. Nourooz-Zadeh J, Tajaddini-Sarmadi J, Ling KL, Wolff SP. Low-density lipoprotein is the major carrier of lipid hydroperoxides in plasma. Relevance to determination of total plasma lipid hydroperoxide concentrations. Biochem J. 1996;313:781–786. doi: 10.1042/bj3130781. [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Nseir W, Shalata A, Marmor A, Assy N. Mechanisms linking non-alcoholic fatty liver disease with coronary artery disease. Dig Dis Sci. 2011;56:3439–3449. doi: 10.1007/s10620-011-1767-y. [DOI] [PubMed] [Google Scholar]
  58. Ohkawa H, Ohishi N, Yagi K. Assay for lipid peroxides in animal tissues by thiobarbituric acid reaction. Anal Biochem. 1979;95:351–358. doi: 10.1016/0003-2697(79)90738-3. [DOI] [PubMed] [Google Scholar]
  59. Parnell JA, Raman M, Rioux KP, Reimer RA. The potential role of prebiotic fibre for treatment and management of non-alcoholic fatty liver disease and associated obesity and insulin resistance. Liver Int. 2012;32:701–711. doi: 10.1111/j.1478-3231.2011.02730.x. [DOI] [PubMed] [Google Scholar]
  60. Qi L, van Dam RM, Liu S, Franz M, Mantzoros C, Hu FB. Whole-grain, bran, and cereal fiber intakes and markers of systemic inflammation in diabetic women. Diabetes Care. 2006;29:207–211. doi: 10.2337/diacare.29.02.06.dc05-1903. [DOI] [PubMed] [Google Scholar]
  61. Quintanilha AT, Packer L, Davies JM, Racanelli TL, Davies KJ. Membrane effects of vitamin E deficiency: bioenergetic and surface charge density studies of skeletal muscle and liver mitochondria. Ann NY Acad Sci. 1982;393:32–47. doi: 10.1111/j.1749-6632.1982.tb31230.x. [DOI] [PubMed] [Google Scholar]
  62. Radulian G, Rusu E, Dragomir A, Posea M. Metabolic effects of low glycaemic index diets. Nutr J. 2009;8:5. doi: 10.1186/1475-2891-8-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Rebello CJ, Liu AG, Greenway FL, Dhurandhar NV. Dietary strategies to increase satiety. Adv Food Nutr Res. 2013;69:105–182. doi: 10.1016/B978-0-12-410540-9.00003-X. [DOI] [PubMed] [Google Scholar]
  64. Rodríguez-Hernández H, Cervantes-Huerta M, Rodríguez-Moran M, Guerrero-Romero F. Decrease of aminotransferase levels in obese women is related to body weight reduction, irrespective of type of diet. Ann Hepatol. 2011;10:486–492. doi: 10.1016/S1665-2681(19)31517-0. [DOI] [PubMed] [Google Scholar]
  65. Ruan H, Dong LQ. Adiponectin signaling and function in insulin target tissues. J Mol Cell Biol. 2016;8:101–109. doi: 10.1093/jmcb/mjw014. [DOI] [PMC free article] [PubMed] [Google Scholar]
  66. Sánchez A, Martínez P, Muñoz M, Benedito S, García-Sacristán A, Hernández M, et al. Endothelin-1 contributes to endothelial dysfunction and enhanced vasoconstriction through augmented superoxide production in penile arteries from insulin-resistant obese rats: role of ETA and ETB receptors. Br J Pharmacol. 2014;171:5682–5695. doi: 10.1111/bph.12870. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Seo MJ, Lee OH, Choi HS, Lee BY. Extract from edible red seaweed (Gelidium amansii) inhibits lipid accumulation and ROS production during differentiation in 3T3-L1 cells. Prev Nutr Food Sci. 2012;17:129–135. doi: 10.3746/pnf.2012.17.2.129. [DOI] [PMC free article] [PubMed] [Google Scholar]
  68. Tanaka T, Ogura R, Hidaka T, Sugiyama M, Pharm B. Changes of electron spin resonance membrane fluidity in hexadecane-induced hyperproliferative epidermis. J Investig Dermatol. 1989;93:682–686. doi: 10.1111/1523-1747.ep12319876. [DOI] [PubMed] [Google Scholar]
  69. Vial G, Dubouchaud H, Couturier K, Cottet-Rousselle C, Taleux N, Athias A, et al. Effects of a high-fat diet on energy metabolism and ROS production in rat liver. J Hepatol. 2011;54:348–356. doi: 10.1016/j.jhep.2010.06.044. [DOI] [PubMed] [Google Scholar]
  70. Volek JS, Phinney SD, Forsythe CE, Quann EE, Wood RJ, Puglisi MJ, et al. Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet. Lipids. 2009;44:297–309. doi: 10.1007/s11745-008-3274-2. [DOI] [PubMed] [Google Scholar]
  71. Volynets V, Machann J, Küper MA, Maier IB, Spruss A, Königsrainer A, et al. A moderate weight reduction through dietary intervention decreases hepatic fat content in patients with non-alcoholic fatty liver disease (NAFLD): a pilot study. Eur J Nutr. 2013;52:527–535. doi: 10.1007/s00394-012-0355-z. [DOI] [PubMed] [Google Scholar]
  72. Weil BR, Westby CM, Van Guilder GP, Greiner JJ, Stauffer BL, DeSouza CA. Enhanced endothelin-1 system activity with over-weight and obesity. Am J Physiol Heart Circ Physiol. 2011;301:H689–H695. doi: 10.1152/ajpheart.00206.2011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  73. Xiao H, Fang J, Lu X, Liu Z, Chen X, Liu J, et al. Protective effect of soluble fiber from Undaria pinnatifida on vascular endothelium in hypercholesterolemic rabbits. Can J Anim Sci. 2009;89:361–367. doi: 10.4141/CJAS08132. [DOI] [Google Scholar]
  74. Yang TH, Chiu CY, Lu TJ, Liu SH, Chiang MT. The anti-obesity effect of polysaccharide-rich red algae (Gelidium amansii) hot-water extracts in high-fat diet-induced obese hamsters. Mar Drugs. 2019;17:E532. doi: 10.3390/md17090532. [DOI] [PMC free article] [PubMed] [Google Scholar]
  75. Yang TH, Yao HT, Chiang MT. Red algae (Gelidium amansii) hot-water extract ameliorates lipid metabolism in hamsters fed a high-fat diet. J Food Drug Anal. 2017;25:931–938. doi: 10.1016/j.jfda.2016.12.008. doi: 10.1016/j.jfda.2016.12.008. Available from: [DOI] [PMC free article] [PubMed] [Google Scholar]
  76. Younossi ZM. Non-alcoholic fatty liver disease–a global public health perspective. J Hepatol. 2019;70:531–544. doi: 10.1016/j.jhep.2018.10.033. [DOI] [PubMed] [Google Scholar]

Articles from Preventive Nutrition and Food Science are provided here courtesy of Korean Society of Food Science and Nutrition (KFN)

RESOURCES