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Wednesday, 6 July 2016

Changes of body composition and circulating adipokines in response to Nigella sativa oil with a calorie restricted diet in obese women

Journal of Herbal Medicine
Volume 6, Issue 2, June 2016, Pages 67–72
Research paper

doi:10.1016/j.hermed.2016.03.003
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Highlights

•
Nigella sativa with a low-calorie diet decreased weight and fat mass in obese women.
•
Nigella sativa with a low-calorie diet decreased insulin secretion with no changes in insulin sensitivity in obese women.
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Nigella sativa with a low-calorie diet increased serum levels of adiponectin hormone with no changes in PPAR-γ levels in obese women after 8 weeks.

Abstract

Aim

Adipose tissue is an active endocrine organ with a key role in metabolic regulation and hormonal signaling. This study determined the effects of Nigella sativa (NS) oil with a low-calorie diet on body composition and adipokine levels in obese women.

Method

In this double-blind, placebo-controlled, randomized, clinical trial, 50 obese women were recruited. The participants were randomly divided into an NS oil group (n = 25) and a placebo group (n = 25), and each group received either a low-calorie diet with 3 g/day NS oil or a low-calorie diet with 3 g/day placebo for 8 weeks. Body composition and biochemical parameters were measured at the baseline and at the end of the trial.

Results

All 50 participants completed the trial. The participants reported no serious side effects, and the liver enzymes did not change significantly after the intervention. Mean BMI of the participants was 32.0 ± 1.5 kg/m2 at the baseline. NS oil decreased body fat mass (−9.5 vs. −2.9%; p < 0.01) and insulin levels (−29.3 vs. −8.6%; p = 0.04) and increased adiponectin levels (87.5 vs. 39.4%; p = 0.03) in the NS oil group compared to the placebo group after 8 weeks. At the end of the study, changes in BMI, insulin sensitivity, and the nuclear receptor PPAR-γ were not significant.

Conclusion

NS oil supplementation combined with a low-calorie diet can modulate hormone secretion and body composition in obese women. However, more studies are needed to clarify the efficacy of NS oil as an adjunct therapy for obesity management.

Abbreviation

  • ALT, alanine aminotransferase;
  • ANCOVA, analysis of covariance;
  • AST, aspartate aminotransferase;
  • BMI, body mass index;
  • FBS, fasting blood sugar;
  • FM, body fat mass;
  • NS, Nigella sativa;
  • PPAR-γ, peroxisome proliferator-activated receptor gamma;
  • QUICKI, quantitative insulin sensitivity check index;
  • RAS, random allocation software;
  • TQ, thymoquinone

Keywords

  • Nigella sativas;
  • Hormone;
  • Obesity;
  • Body fat distribution

1. Introduction

Adipose tissue is a highly active endocrine organ which plays a key role in energy homeostasis, response to hormone signaling, metabolic regulation, and adipokine secretion. Adipose tissue secretes more than 50 signaling molecules and hormones called adipokines (Harwood, 2012). Adipokines are involved in the regulation of thermogenesis, appetite, glucose metabolism, insulin sensitivity, and other endocrine functions (Harwood, 2012; Gown et al., 2014). Adiponectin, a 30-kDa protein with anti-inflammatory and insulin-sensitizing actions, is an adipokine secreted exclusively from adipose tissue. It is involved in glucose and lipid metabolism and has an important role in decreasing insulin resistance and the risk of cardiovascular diseases (Fiaschi et al., 2014). Another important adipokine and a transcription factor abundantly expressed in adipose tissue is peroxisome proliferator-activated receptor gamma (PPAR-γ). PPAR-γ has key roles in the regulation of fat generation, adipogenic differentiation, and insulin sensitivity (Ahmadian et al., 2013).
In obesity, the normal interaction between signals to and from adipocytes (a hormonal and metabolic feedback system) is disturbed by fat accumulation in the adipocytes. Insulin sensitivity and the secretion of adiponectin and PPAR-γ hormones decrease with obesity, and the risk of atherosclerosis and cardiovascular diseases increases (Torres-Fuentes et al., 2015). Previous studies have reported that adiponectin and PPAR-γ levels increased after losing weight through a calorie-restricted diet (Kotidis et al., 2006; Puglisi and Fernandez, 2008; Verreth et al., 2004). A calorie-restricted diet is the first-line therapy for losing weight. However, due to difficulties in adhering to a low-calorie diet for weight loss, obese subjects, particularly in Eastern societies often have a high tendency to take anti-obesity herbal supplements (Yun, 2010). Some studies have indicated that the medicinal herb, Nigella sativa (NS) has anti-obesity properties ( Datau et al., 2010 and Le et al., 2004; Zaoui et al., 2002; Meddah et al., 2009).
The genus Nigella belongs to the buttercup or Ranunculaceae family. NS, also known as black cumin or black seed, is widely grown in Eastern Europe, the Middle East, and Western Asia. NS contains different active ingredients, including thymoquinone (TQ), thymol, nigellone, nigellicine, alpha-hederin, unsaturated fatty acids, vitamins (B1, B3, B6, E) and minerals (Fe, Zn, Cu) ( Ali and Blunden, 2003; Heshmati and Namazi, 2015). In Iranian traditional medicine, NS has been used to promote health and treat several diseases, such as rheumatoid arthritis, dermatological diseases, digestive disorders, dyslipidemia, and diarrhea (Heshmati and Namazi, 2015; Namazi et al., 2015a). Studies have shown the antimicrobial, immune-stimulatory, anti-inflammatory, antioxidant, anti-diabetic and anti-obesity effects of NS in animal models and clinical trials with no reports of toxicity or serious side effects (Meddah et al., 2009; Heshmati and Namazi, 2015; Ali and Blunden, 2003).
Limited studies have evaluated the effects of NS on obesity and insulin sensitivity with conflicting results (Qidwai et al., 2009, Najmi et al., 2008 and Heshmati et al., 2015). To the best of the author’s knowledge, the present study is the first to evaluate the effects of NS oil combined with calorie restriction on fat-derived hormones in obese subjects. Therefore, the aim of this study was to determine whether NS oil combined with a low-calorie diet could improve body composition and adipokine levels in obese women.

2. Materials and methods

2.1. Participants

Trial subjects consisted of 50 obese females who had visited Sheykhoraees Clinic in Tabriz, Iran between April to July 2014. Inclusion criteria included gender (female), age (between 25 and 50 years), and body mass index (between 30 kg/m2 and 35 kg/m2), while excluded were individuals with a history of cardiovascular, renal, hepatic, diabetes mellitus or pancreatic disorders; a history of smoking; adherence to a weight loss diet or the use of anti-obesity drugs over the past 6 months; consumption of aspirin, vitamin K, or any other anticoagulant drugs; pregnancy and lactation; or the consumption of any herbal medicines, antioxidants or anti-inflammatory medications. General characteristics collected through participant interviews included age, family history of obesity, consumption of medicine, and medical history.

2.2. Study design and randomization

Subjects of the present clinical trial, which involved a randomized double-blind placebo-controlled design, were randomly allocated through a block randomization procedure into two groups based on their body mass index (BMI) and age. Each arm of the trial included two cases in every permuted block, and all case allocations were conducted randomly by RAS (Random Allocation Software). Based on previous research (Datau et al., 2010) and considering body weight changes, sample size was determined. The minimum resulting sample size was calculated at 20 subjects, resulting in a 95% confidence level and 80% power for each treatment group. The sample size was ultimately raised to 25 people to compensate for a 25% dropout rate. The trial was conducted according to the guidelines established in the Declaration of Helsinki, and approved by the Ethics Committee of Tabriz University of Medical Sciences, and informed written consent was obtained from the participants. The trial was registered on the Iranian registry of clinical trials (www.irct.ir/, IRCT201106191197N10).

2.3. Intervention

All the participants received a moderate fat, nutrient-balanced reduction diet. A dietician designed an individual diet by using the Mifflin equation to determine resting energy expenditure (Namazi et al., 2015b). After adding the estimated physical activity coefficient (based on International physical activity questionnaire) and thermic effect of food coefficient (1.1), 500 kcal from the amount of total required daily energy calculated for each subject was subtracted. The resulting diet was composed of 15% protein, 55% carbohydrates, and 30% fat. A 24-hour dietary recall (one weekend day and two weekdays) was applied for assessing the level of patients’ compliance with the diet.
NS oil soft gel capsules were administered to the treatment group for 8 weeks at a dose of 3 g/day, with patients ingesting one capsule (1 g NS oil) 30 min before each main meal (breakfast, lunch and dinner), and the same dosage of sunflower oil (SF) was given to the placebo group. Similar opaque bottles were used to present both capsules of NS oil and SF oil to participants. Half of the bottles were distributed among subjects at the beginning of the trial, and the remaining bottles were distributed in the middle of the trial. After randomization, volunteers received supplements in compliance with allocation codes. In order to maintain ‘blinding’, this procedure was carried out by an investigator who had no clinical involvement in the study. In addition to participants, clinical and laboratory staff were kept ‘blind’ until the end of data analyses to ensure reliable randomization and allocation. Contact with subjects was maintained through a weekly phone call in an effort to minimize dropouts and to make sure that participants were ingesting assigned supplements. Volunteers were asked to inform research staff immediately in the event of any suspicious reactions to supplements. Participants were also asked not to change physical activities and to inform researchers if they consumed any drugs or changed their physical activities during the experimental period. Upon returning their bottles to researchers after the trial, participants’ compliance with the plan was determined by counting remaining capsules in each bottle. Patients who had consumed fewer than 95% of the supplements in each visit were excluded from the trial.

2.4. Characteristics of supplements

Soft gel capsules of NS oil and SF oil, similar in color and size, were prepared by Daana Pharmaceutical Company. (Tabriz, Iran). A cold press procedure with a yield of 30% was used to prepare the NS oil, and measurements of fatty acid content of both oil supplements were presented in our earlier study (Mahdavi et al., 2015). Sunflower oil was chosen as a placebo based on previous studies (Gonzales and Gonzales, 2014; Ballard et al., 2002). Participants and researchers were not aware of treatment details, and bottles containing capsules were coded as A or B by an individual who was not involved in the trial.

2.5. Measurements

The primary outcomes of the present study based on the aims of study were the effects of NS oil supplementation with a low-calorie diet on BMI, serum levels of insulin, adiponectin, peroxisome proliferator-activated receptor γ (PPAR-γ) and insulin sensitivity in obese women. The secondary outcome was the effects of NS oil supplementation with a low-calorie diet on liver enzymes in obese women. At baseline, and at the end of the study, anthropometric indices, physical activity, dietary intake and biochemical parameters were evaluated. Measurement of anthropometric indices, physical activity and dietary intake were described elsewhere (Mahdavi et al., 2015).

2.5.1. Body composition assessment

To evaluate the percentage of body fat mass (FM) and muscle, bioelectrical impedance analysis (Omron BF-508, Omron Medizintechnik, Mannheim, Germany) was used with an accuracy of ±0.1% for FM and muscle. All participants were requested to avoid any food or beverage intake and intensive exercise for at least4 h before measurement.

2.5.2. Blood sampling and biochemical measurements

After 12–14 h of fasting, 5 mL venous blood samples were collected to measure fasting blood sugar (FBS), aspartate aminotransferase (AST), alanine aminotransferase (ALT), insulin, adiponectin, and PPAR-γ levels at the baseline and at the end of the trial. The serum samples were separated from the whole blood by centrifugation at 2500 rpm for 10 min (Beckman Avanti J-25; Beckman Coulter, Brea, CA) at room temperature. FBS was measured using COBAS 6000 autoanalyzer (Roche Company, Germany) with a commercial kit (Pars Azmoon Co., Iran) immediately after collection. The remaining serum was stored at −80 °C until needed for the assay. Insulin, PPAR-γ, and adiponectin concentrations were measured with commercial ELISA kits (Orgenium, Finland). The liver enzymes (AST and ALT) were measured with photometry method using commercial kits (Pars Azmoon, Iran). Insulin sensitivity was determined with the quantitative insulin sensitivity check index (QUICKI) by the following formula: (1/log insulin (μU/ml) +log glucose (mg/dl)) (Hrebicek et al., 2002).

2.6. Statistical analysis

All data were analyzed using SPSS software version 16.0 (SPSS, Chicago, IL, USA). The normality of data distribution was evaluated by the One-sample Kolmogorov-Smirnov test. Quantitative data with normal and non-normal distribution were reported as mean ± SD and median (25th, 75th percentiles), respectively. Paired t-test and Wilcoxon test were used to compare within group differences of parametric and nonparametric variables, respectively.
Comparison of differences at baseline between the two study groups were assessed using independent sample t test for normally distributed parameters and the Mann–Whitney test for nonparametric data. To avoid potential bias, analysis of covariance (ANCOVA) was used for adjusting known confounder factors (body weight changes, dietary intake changes and baseline values). For calculating the percentage of mean changes of markers, at the beginning and at the end of the study (after 8 weeks), mean changes of markers from baseline were calculated in each group by [(8 weeks values-baseline values)/(baseline values)] × 100. The significance level was set at p < 0.05.

3. Result

All the participants (n = 50) completed the trial (Fig. 1). The capsule counts indicated that all the participants had high compliance (>95%) with the supplementation. The subjects reported no serious side effects, except for mild, temporary stomachaches, throughout the intervention. The participants were premenopausal females with the mean age and BMI of 40.0 ± 10.0 years and 32.0 ± 1.5 kg/m2, respectively. The NS oil group and SF oil group were similar in their baseline characteristics (Table 1).
Fig. 1
Fig. 1.
Flow diagram of participants recruitment and randomization process.
Figure options
Table 1. Baseline characteristics of the study participants.
VariablesNS oil group (n = 25)SF oil group (n = 25)
Age (year)41.01 ± 11.81*39.50 ± 9.81
Weight (Kg)81.02 ± 10.0079.00 ± 10.52
Body Mass Index (kg/m2)32.53 ± 1.5131.60 ± 1.52
Family history of obesity (%)80.0084.00

Physical activity (%)
Sedentary72.0076.00
Moderate28.0024.00
*
Mean ± SD.
Table options
Both groups received a low-calorie diet, therefore energy intake decreased in the two study groups compared to the baseline. However, no significant differences were seen in the energy and macronutrient intake between the NS oil and SF oil groups after the intervention. Table 2 shows the two groups’ BMIs and body compositions. No significant differences were seen in body composition, except in FM, between the two groups at the start of the study (p = 0.04). After 8 weeks, BMI and body composition (FM, muscle and visceral fat) decreased in both groups (p < 0.01 for all variables). However, when adjusted for dietary intake changes and baseline values, NS oil supplementation with a calorie-restricted diet led to a significant decrease in FM (−9.5 vs. −2.9%; p < 0.01) with no significant changes in BMI, compared to the SF group. Despite a high reduction in visceral fat (−7.3 vs. −5.6%) in the NS oil group compared to that in the SF group, visceral fat differences between the two groups were not significant (p = 0.1).
Table 2. Comparison of BMI, body composition and biochemical parameters between NS oil group and SF oil group at baseline and after the intervention.
VariableNS oil group (n = 25)SF oil group (n = 25)P-valueb
BMI (kg/m2)
Baseline32.41 ± 1.50a31.62 ± 1.300.06
End31.81 ± 1.6031.22 ± 1.210.22d
Pre to post P-valuec<0.01*<0.01*

Fat mass (%)
Baseline45.61 ± 2.8143.40 ± 4.400.04
End42.01 ± 3.8242.61 ± 4.10<0.01* and d
Pre to post P-valuec<0.01*<0.01*

Muscle mass (%)
Baseline24.02 ± 1.4124.90 ± 2.110.1
End25.12 ± 1.9025.21 ± 1.800.19d
Pre to post P-valuec<0.01*<0.01*

Visceral fat
Baseline9.22 ± 1.618.40 ± 2.100.12
End8.41 ± 1.608.00 ± 2.010.14d
Pre to post P-valuec<0.01*<0.01*
a
Mean ± SD.
b
Independent t-test.
c
Paired t-test.
d
Analysis of covariance (adjusted for dietary intake changes and baseline values).
*
P < 0.05 considered significant.
Table options
At the baseline, no significant differences were found in the biochemical parameters, except for the PPAR-γ and FBS levels (p < 0.05 for both variables), in the two study groups. Comparison within the groups indicated that adiponectin levels and QUICKI increased and insulin concentrations decreased significantly in the NS oil group after 8 weeks of intervention. However, only the changes in adiponectin (87.5 vs. 39.4%; p = 0.03) and insulin levels (−29.3 vs. −8.6%; p = 0.04) were significant between the two groups (ANCOVA adjusted for energy intake changes, weight changes, and baseline values). Moreover, liver enzyme comparisons within and between the groups showed no significant differences at the end of the study (Table 3).
Table 3. Comparison of biochemical parameters between NS oil group and SF oil group at baseline and after the intervention.
VariableNS oil group
(n = 25)		Placebo group
(n = 25)		P-valueb
adiponectin (μg/mL)
Baseline36.43 ± 15.91a43.33 ± 20.840.21
End56.81 ± 25.0448.80 ± 26.820.01d and *
Pre to post P-valuec<0.01*0.12

PPAR-γ (ng/mL)
Baseline19.01 (16.40, 30.31)f23.01 (16.41, 89.8)0.04h and *
End36.72 (17.52, 56.01)36.4 (29.93,59.11)0.20d
Pre to post P-valueg0.02*0.01*

FBS (mg/dL)
Baseline102.82 ± 10.6793.93 ± 6.55<0.01
End103.05 ± 9.1795.60 ± 8.910.41d
Pre to post P-valuec0.120.31

Insulin (μU/mL)
Baseline6.22 ± 2.806.02 ± 2.540.83
End4.15 ± 2.515.41 ± 2.800.03d and *
Pre to post P-valuec<0.01*0.2

QUICKI
Baseline0.36 ± 0.020.37 ± 0.020.48e
End0.39 ± 0.030.38 ± 0.03
Pre to post P-valuec<0.01*0.240.20d

AST (U/L)
Baseline16.60 ± 2.9117.41 ± 3.020.31e
End16.11 ± 2.5017.01 ± 3.430.82d
Pre to post P-valuec0.430.75

ALT (U/L)
Baseline15.50 ± 2.7116.61 ± 3.000.24e
End15.04 ± 3.4416.83 ± 4.300.30d
Pre to post P-valuec0.720.90
a
Mean ± SD.
b
Independent t-test.
c
Paired t-test.
d
Analysis of covariance (adjusted for dietary intake changes, weight changes and baseline value.
e
Analysis of covariance (adjusted for FBS at baseline).
f
Values are presented as median (25th, 75th percentiles) for nonparametric variable.
g
Wilcoxon test.
h
Mann Whitney U test.
*
P < 0.05 considered significant.
Table options

4. Discussions

In the present study, NS oil supplementation concurrent with a low-calorie diet decreased FM, and insulin levels and increased adiponectin with no serious side effects after the 8-week intervention. It seems that no clinical trials have evaluated efficacy of a weight-loss diet plus NS oil as an adjutant therapy versus a weight-loss diet alone on obesity management.

4.1. Effects of NS oil on anthropometric indices and body composition

Few studies have evaluated the effects of NS on anthropometric indices, and those studies have had conflicting results (Datau et al., 2010, Najmi et al., 2008 and Qidwai et al., 2009). The author’s findings were in line with various studies. Najmi et al. concluded that 5 mL/day NS oil reduced BMI in subjects with metabolic syndrome after 6 weeks, but the reduction was not significant compared to the placebo group (Najmi et al., 2008). In addition, Qidwai et al. (2009) indicated that 2 g/day NS powder did not reduce BMI in healthy adults after 6 weeks. It seems that there has been no clinical trial that has evaluated the effects of NS on body composition. Due to possible synergetic effects of NS oil supplement concurrent with a low-calorie diet in the present study, weight decreased more than that seen in the previous studies. Although no changes were observed in BMI value between the two groups, FM decreased after the intervention. According to participant interviews, the NS oil supplement helped the participants adhere to the low-calorie diet due to its satiating power, as was reported by other studies (Le et al., 2004; Zaoui et al., 2002). In the present study, three-day (two weekdays and one weekend), 24 h food recall was used for evaluation of energy intake. Reduction in energy intake of NS oil group was more than the placebo group at the end of the trial. Most studies on changes in dietary intake after NS oil supplementation were done in animal models (Le et al., 2004; Zaoui et al., 2002; Meddah et al., 2009). Le et al. (2004) indicated that intragastric gavage of 2 g/kg/day petroleum ether extract of NS reduced food intake and body weight in rats after 4 weeks. In a study by Meddah et al., (2009) 2 g/kg/day aqueous extract of NS intraperitoneally reduced weight in rats. Zaoui et al. (2002) also reported that 2 mL/kg/day of NS oil intraperitoneally decreased weight in rats after 12 weeks. A reduction in appetite and food intake plus effective constituents of NS such as TQ and thymol, that affect lipid metabolism and insulin secretion, as suggested by the animal studies may be potential anti-obesity mechanisms for NS. As one of the barriers to adherence to a weight-loss diet is a strong appetite, NS oil might be a suitable supplement for a low-calorie diet in obese women.

4.2. Effects of NS oil on insulin secretion and adipokines

In this study, NS oil combined with calorie restriction decreased insulin levels with no changes in FBS levels and QUICKI after 8 weeks of intervention. A few clinical trials have been conducted on the glycemic effects of NS, and the findings of the present study were in line with these studies on insulin secretion. Heshmati et al. (2015) found that 3 g/day NS oil decreased FBS,insulin levels and insulin resistance in patients with type 2 diabetes after 3 months. Hadi et al. reported that 1 g/day of NS oil decreased FBS concentrations after 8 weeks in patients with type 2 diabetes (Hadi et al., 2015). Bamosa (2015) also indicated that 2 g/day of NS seed decreased FBS and insulin resistance in patients with type 2 diabetes after 3 months. In regard to insulin sensitivity and FBS levels the author’s results conflicted with previous studies. However, the present study was in line with a study by Datau et al. (2010) in which 3 g/day NS powder did not change FBS levels after 3 months in men with abdominal obesity.
Overall, subjects with higher biochemical parameters at the start of the study were also those who had a greater decline in those biochemical levels after the intervention (Mahdavi et al., 2015). In this study, mean FBS levels were not very high at the baseline; therefore, changes in FBS levels were less than that seen in the previous studies. However, differences in background disease, dosage and type of NS supplementation, duration of intervention, dietary pattern, physical activity level, or race may lead to different findings.
A possible mechanism for the reduction of insulin is the loss of body weight and FM. However, in the present study, weight and dietary intake changes were controlled by using the ANCOVA analysis to compare the two study groups. Therefore, the inter group differences in insulin levels is probably not due to losing weight. Another potential mechanism may be related to the components of NS. Evidence indicates that long-chain fatty acids are agonist to the PPAR-γ gene and they are involved in obesity, energy homeostasis, and insulin resistance (Selvaraj et al., 2010). In the present study, slight differences were observed between the fatty acid contents of NS oil and SF oil (Mahdavi et al., 2015). Therefore, it seems that the effects of fatty acids (type and amount) of NS are not strong enough to result in losing weight. The antioxidant components of NS oil, particularly TQ, may also improve the intracellular pathways of insulin receptors and increase insulin sensitivity. NS was reported to stimulate acetyl-CoA carboxylase phosphorylation, participate in the AMPK signaling pathway, act as an insulin-sensitizing factor in muscle and liver, and increase muscle GlUT-4 expression (Benhaddou-Andaloussi et al., 2010).
The present study indicated that NS accompanied by a low-calorie diet increased adiponectin levels after 8 weeks. Clinical trials on the effects of NS on adipokines are limited. Only Datau et al., 2010 evaluated the effects of NS on adiponectin levels in a human model. Our finding was contrary to Datau et al.’s study. They indicated that despite the significant reduction in weight after taking 3 g/day NS powder, no significant changes were observed in adiponectin levels in men with abdominal obesity after 3 months (Datau et al., 2010). Ryan et al. (2003) reported that a weight-loss diet decreased FM, BMI, and insulin concentrations with no changes in adiponectin levels in overweight and obese women after 6 months. This study however was in accordance with the Madsen et al. (2008) study. They found that a calorie-restricted diet decreased adiponectin levels in obese women after 8 weeks (Madsen et al., 2008). Differences in these findings can be due to differences in BMI at the baseline, reduction rate in weight and FM during the intervention, energy intake, or type of intervention.
It has been indicated that adiponectin modulates the interaction between obesity and insulin resistance, and a reduction in weight and FM increases plasma levels of adiponectin. Due to feedback inhibition, a greater loss of FM results in a larger rise in adiponectin levels (Yamauchi et al., 2001 and Madsen et al., 2008). In the present study, after a drop in insulin concentrations and FM, and a rise in insulin sensitivity, an increase in adiponectin levels was expected. Although changes of insulin sensitivity were not significant between two groups, the amount of QUICKI changes may be involved in improvement of adiponectin levels.
Another fat-derived hormone measured in the present study was PPAR-γ. An increase in PPAR-γ levels was seen in the NS oil group after the intervention but no significant differences were observed in PPAR-γ levels between the two groups. No clinical trials have evaluated the effects of NS on PPAR-γ levels. Recently, an In vitro study has reported that TQ can act as a ligand of PPAR-γ and increase PPAR-γ activity ( Woo et al., 2011). However more studies are needed to clarify possible effects of NS and its constituents on PPAR-γ function.
This is the first clinical trial to evaluate the effect of NS oil with a calorie-restricted diet on the metabolic features of obesity. The present study had the following limitations: (1) the effect of NS oil without a low-calorie diet was not evaluated; (2) only female subjects were included and (3) the intervention was limited to eight weeks and its effect over longer periods is not clear. Its strengths were that it was double-blinded and the biochemical parameters were adjusted for some of the known confounding factors. Further studies are recommended to (1) add a third arm to study the pure effect of NS oil on obesity management, (2) evaluate the effects of NS in different dosages and forms (extract, oil, powder), (3) measure appetite hormones and (4) determine the effects of NS on gene expression of adiponectin and PPAR-γ.

5. Conclusions

NS oil supplementation concurrent with a low-calorie diet may improve body composition and hormone secretion in obese women. However, more studies are needed to clarify the efficacy of NS oil as an adjunct therapy for obesity management.

Conflict of interest

Authors declared no conflict of interest

Acknowledgment

We are grateful to the participants for their cooperation. The authors also would like to thank Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran for funding of the project. The results of this article are derived from PhD thesis of Nazli Namazi.

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