This is the first study which directly compared the effects of RSO or ASO supplementation on weight loss, as well as anthropometric and metabolic parameters, of obese participants of a weight loss program. RSO and ASO are characterized by a sizeable difference in fatty acid composition. ASO contains lower amounts of MUFAs (~24% vs. ~59%) and LC n-3 PUFAs (~1% vs. ~11%) and displays poorer PUFA/SFA and USFA/SFA ratios compared with those of RSO. Furthermore, ASO has a lower n-3/n-6 ratio than that of RSO . By contrast, ASO is an oil with one of the highest squalene content. Strong anticancer, antioxidant, drug carrier, detoxifier, skin hydrating and emollient activities of squalene have been reported in both animal models and in vitro environments .
In contrast to studies based on long-term body mass reduction protocols, the current study evaluated whether a short-term weight loss program, conducted under strictly controlled conditions, would induce satisfactory anthropometric and metabolic changes in adult patients with obesity.
A previous study showed that the replacement of usual edible oils with oils rich in USFAs, such as ASO and RSO, resulted in lipid-modulating, anti-atherogenic, antioxidative, anti-inflammatory, hepatoprotective and hypotensive effects [7, 12]. The properties of dietary fat reportedly modulated obesity by interacting with genes encoding fatty acid metabolism, adipogenesis and endocannabinoid system .
Animal studies have indicated that LC n-3 PUFAs may protect against weight gain, raising the possibility that LC n-3 PUFA facilitates weight loss or differential changes in body composition when incorporated into weight-loss programs . Furthermore, Borsonelo et al.  demonstrated anxiolytic-like effects of PUFA enriched diets on animal anxiety models. A time-dependent effect of LC n-3 PUFAs on weight loss in humans has been reported [25, 26]. Certain studies have shown that MUFAs that induce higher energy expenditure, diet-induced thermogenesis, and fat oxidation than that by PUFA diets, may affect weight loss more effectively than PUFAs [27, 28]. However, the current study was unable to confirm whether oil supplementation during a weight reduction program increases the effectiveness of interventions. At the end of the study, significant reductions in weight, BMI, WC, HC, and FM were observed in each group, and also in subjects from the control group. Except for WC, HC and VFM, no significant differences were observed in weight loss or other anthropometric parameters between groups. Weight loss and improvement in body composition observed in this study were comparable with those observed in other studies [29, 30]. It is noteworthy that the most significant reduction in VFM was observed in patients without oil supplementation, although it did not result in an improvement in metabolic parameters.
Numerous studies have indicated that consumption of high levels of MUFAs and PUFAs may improve glucose metabolism and lipid profile, compared to the consumption of fats containing higher levels of SFAs. However, whether replacement of dietary SFAs with higher concentrations of MUFAs or PUFAs would further enhance metabolic parameters remains unclear [31, 32]. A meta-analysis conducted by Qian et al.  revealed that, consumption of MUFA-rich diets resulted in significant reduction in fasting plasma glucose and a nonsignificant reduction in fasting insulin, TG, and LDL levels, compared to consumption of high-PUFA diets. By contrast, Miller et al.  demonstrated that substituting SFA with PUFAs in metabolic syndrome patients resulted in a higher reductions of TG and improved endothelial function than MUFAs.
The current study did not indicate any differences between intervention induced changes in the clinical parameters of AO, RO and C, except in HOMA-IR. HOMA-IR was most markedly reduced in the OR group, while an increase in HOMA-IR was noticed in the C group. However, there was a trend toward significantly reduced fasting serum insulin levels and HDL% in AO and RO groups, as opposed to the C group. Additionally, statistically significant changes in the fasting glucose level, TC, non-HDL, TG/HDL ratio, LDL and TG were observed in the AO group.
Previous studies have suggested that RSO may be used to normalize glucose profiles in humans [34-36]. A study of type 2 diabetes patients treated with an oral antihyperglycemic agent at a Canadian academic center, showed that consuming a canola oil-enriched low-glucose diet for 3 months improved glycemic control . The effect of ASO on glucose metabolism was less clear. Kim et al., showed that 3 weeks of ASO supplementation (100 mg/kg) significantly reduced serum glucose levels in streptozocin-induced diabetic rats . The beneficial effect of ASO in patients with diabetes mellitus type 2 has also been confirmed by Miroshnichenko et al. . The current study observed significant improvements in fasting insulin levels and insulin sensitivity in the AO and RO groups, although changes in glucose levels were observed only in subjects supplemented with ASO.
The effect of RSO on circulatory cholesterol levels has been reported in most short-term interventions . Lin et al.  demonstrated that diets rich in RSO resulted in substantial reductions in TC (12.2-12.5%) and LDL levels (17%). However, changes induced in HDL and TG levels by canola oil were evidently inconsistent. Furthermore, previous studies have reported that compared to consumption of high-SFA diets, consumption of diet enriched with RSO resulted in 8-10% reduction in HDL concentrations [39-41]. Data from this study showed that a calorie-restricted RSO-supplemented diet does not significantly affect TC and TG levels. A slight increase in HDL concentration and improvement in non-HDL and TG/HDL ratios were observed, but these changes were not statistically significant.
The beneficial effect exerted by ASO on cholesterol and bile acid absorption, cholesterol lipoprotein distribution, hepatic cholesterol content and cholesterol biosynthesis was demonstrated by Berger et al. , via an animal model study. In this study, hamsters were given hypercholesterolemic diets consisting of control, 10, or 20% Amaranthus cruentus grain, or 2.5 or 5% crude amaranth oil for 4 weeks. The results showed that amaranth oil (5%) significantly decreased TC HLD and VLDL, compared to the control, and increased fecal excretion of particular neutral sterols and the bile acid, ursodeoxycholate . However, an animal study  and a human pilot study  conducted by Berber et al., revealed that cholesterol-lowering properties of ASO did not affect lipid profiles in an identical manner, and that the final effect of ASO on cholesterol metabolism may depend on factors such as amaranth species and cultivars, growing and processing conditions, as well as unique nutritional compositions
Gonor et al. , investigated the beneficial effects exerted by a diet supplemented with squalene (600 mL/d) from amaranth oil (18 mL/d) on TC and TG concentrations and the fatty acid composition of erythrocytes, in patients with ischemic heart disease and hyperlipoproteinemia. Similarly, Martirosyan et al. , showed that 3 weeks of exposure to low-sodium/low-fat diets containing ASO (3, 6, 12, or 18 mL/d) promoted positive dose-dependent changes in serum TC, LDL and TG levels in obese patients with coronary heart disease and hypertension.
The current study revealed that a 3-week intervention with ASO supplementation (20 mL/d) led to a significant reduction in TC, %HDL, LDL, and TG levels and caused a slight, nonsignificant, increase in HDL levels. Statistically significant improvements in non-HDL and TG/HDL levels were also observed in the AO group. Although, ASO contains lower amounts of MUFA and LC n-3 PUFA than RSO, the presented study demonstrated that ASO caused more marked changes in lipid profiles than RSO. A better understanding of reasons underlying this finding may require further investigation.
The results of the current study showed that supplementation with ASO and RSO during the 3-week body mass reduction program did not cause changes in anthropometric measurements and clinical outcomes that were more effective, compared to group C. However, the study revealed a trend toward a more marked improvement in carbohydrate and lipid profiles in AO and RO groups compared with that in group C.
Study strengths and limitations
The strength of this study is that the intervention was conducted under strictly controlled conditions. During the 3-weeks program, the participants were in the hospital ward, being under constant control over diet, supplementation and physical activity. The major limitations of this trial were small sample size and the relatively short duration of intervention. The main reason for such a short duration was that continued hospitalization for 3 weeks may interrupt professional and personal activities. However, it is noteworthy that presented study was one of the few studies conducted under specific and strictly controlled conditions, which is rare in nutritional interventions. Participants of the study received the same type of hypocaloric diet prepared by a dietetic food caterer and underwent the same physical activity program with a physical therapist. The 3-week hospitalization allowed the involvement of the study population in the intervention to be controlled. Although dual energy X-ray absorptiometry (DXA) is the gold standard for the assessment of body composition, the bioimpedance method (BIA) was used in the study due to its non-invasiveness, lower cost, and widespread use.