The purpose of this double-blind, randomized dietary intervention was to examine the effect of SO consumption in the context of a weight loss program on glycemic control markers, inflammation, and oxidative stress among women with NAFLD for 84 days. Findings showed that SO improved glycemic control markers, including FBG, FSI, HOMA-IR, and QUICKI, while it had no effects on hs-CRP and MDA levels.
Nowadays, the role of different dietary approaches in the management of NAFLD has received significant attention (Parra-Vargas, Rodriguez-Echevarria, & Jimenez-Chillaron, 2020); Some nutritional components, such as the phytochemical, antioxidants, MUFAs, and PUFAs, exist in SO, are related to a reduced risk of chronic diseases (Farajbakhsh et al., 2019). No study has examined the beneficial effects of SO on patients with NAFLD. Moreover, the number of studies concerning the effects of SO on glycemic indices, inflammation, and oxidative stress in other diseases is limited.
Glycemic Control Markers
Some studies have assessed the effect of SO consumption on glycemic control markers. Our results are in line with some studies; A meta-analysis study showed that SO consumption reduced FBG (Atefi, Entezari, Vahedi, & Hassanzadeh, 2022). Farajbakhsh et al. showed that consuming 30 ml/day SO for eight weeks in metabolic syndrome patients caused a significant decrease in FBG and FSI levels (Farajbakhsh et al., 2019). Similar results with SO consumption in lowering FBG were observed in other studies (Aslam et al., 2019; Mitra, 2007; Mosallaieepour-Yazdi, Eghtesadi, Kaseb, Afkhami-Ardakani, & Hoseini, 2008; D. Sankar, Ramakrishna Rao, Sambandam, & Pugalendi, 2006; Devarajan Sankar, Ali, Sambandam, & Rao, 2011). Furthermore, a study showed that SO significantly reduced FBG and FSI levels in male Sprague-Dawley rats (Aslam et al., 2017).
Several studies had relatively different results from our research; For example, a meta-analysis study showed that SO consumption had no significant effect on FSI (Atefi et al., 2022). In a cross-over study, 95 patients with type 2 diabetes substituted SFO with SO for nine weeks. The results showed that SO consumption did not significantly change FBG. While, in this trial, a set dosage for oil consumption was not performed. These differences in consumption levels may be the reason for the lack of significant reduction in FBG (Raeisi-Dehkordi et al., 2021). In a parallel study, Aslam et al. reported that consumption of 30 ml /day SO for 90 days in diabetic patients significantly increased FSI, but HOMA-IR was unaltered (Aslam et al., 2019). Differences in participants' disease, SO dosage, and study design may be the reason for the difference between the results of our study and this study.
Our study showed that following SO compared with SFO lessened glycemic control markers. These beneficial effects may be related to the fatty acid profiles in SO, where MUFAs in the SO group were significantly higher than in the SFO group after the intervention. A meta-analysis of RCTs showed that dietary fats, including SFAs, MUFAs, and PUFAs, had different effects on glycemic control markers and their homeostasis (Imamura et al., 2016). A study has shown that replacing foods with high SFAs with foods with high MUFAs could be effective in controlling blood glucose in patients with diabetes (Risérus, Willett, & Hu, 2009). A diet high in MUFAs brings protective effects against pancreatic beta-cell death, and in this way, it improves glycemic control and increases insulin sensitivity (Paniagua et al., 2007). The contents of MUFAs in SO can increase the PUFAs’ effect on FBG and FSI. However, the exact mechanism of association of MUFAs with glucose homeostasis and IR is unclear. MUFAs may ameliorate glycemic tolerance through an increase in the secretion of glucagon-like peptide-1 (Rocca, Lagreca, Kalitsky, & Brubaker, 2001). Also, they can act on the gene expression involved in lipid metabolism and consequently improve the fatty acid composition and reduce IR (Yang, Miyahara, Mori, Doisaki, & Hatanaka, 2011).
SO contains antioxidant compounds (11.51 mg/g lignans and 40 mg/ 100 g α-tocopherol) that may contribute through producing reactive oxygen species (ROS) scavenging effects, beta cells protection from death, and insulin secretion improvement (Nakai et al., 2003; Yargholi et al., 2021). It has been reported that lignans, by increasing the expression of genes involved in carbohydrate metabolism and insulin signal transduction pathways, play a role in controlling blood glucose in diabetic rats (Aslam et al., 2019; Bigoniya, Nishad, & Singh, 2012). In addition, sesamin, a lignans of SO, can prevent the increase of blood glucose by increasing glycogen synthase (Hong et al., 2013).
Inflammation And Oxidative Stress
The hs-CRP is known as a marker of inflammation in chronic disease (Burmeister et al., 2014). One of the main markers of oxidative stress is MDA (Halliwell & Whiteman, 2004; Periasamy, Chien, et al., 2014). It has been reported that there is a link between inflammation and oxidative stress, so an increase in the levels of oxidative stress can lead to an increase in the concentration of inflammatory factors (Burgos-Morón et al., 2019). In the current study, after 12 weeks of SO dietary intervention in women with NAFLD, we found no significant changes in hs-CRP and MDA levels.
A number of systematic review studies showed favorable effects of sesame consumption and its derivatives on oxidative stress and inflammatory biomarkers (De Almeida Vittori Gouveia, Cardoso, De Oliveira, Rosa, & Moreira, 2016; E. Hsu & Parthasarathy, 2017; Rafiee et al., 2021). Our study examined the effects of SO on the mentioned indicators, which differs from these studies.
A clinical trial study has reported that eight weeks of SO consumption in patients with metabolic syndrome reduced serum MDA levels while hs-CRP levels remained unchanged (Farajbakhsh et al., 2019). In a parallel study, Aslam et al. assessed patients with diabetes that ingested 30 ml of SO for 90 days. After the intervention, MDA levels decreased in the SO group (Aslam et al., 2019). Differences in participants' disease and study design may be the reason for the difference between the results of our study and these studies.
An RCT in patients with hypertension that was randomized to either SO and nifedipine (as intervention group) or nifedipine (as control group). After 60 days, MDA levels decreased following the intervention group (D. Sankar, Sambandam, Ramakrishna Rao, & Pugalendi, 2005). In this study, the simultaneous effect of the drug with SO has been investigated and all of these effects cannot be attributed to SO.
Another study (45 days intervention) found favorable effects of 35 g of SO on MDA of hypertensive diabetics patients (D. Sankar et al., 2006). In this study, the results may not be reliable because there was no control group.
Strengths And Limitations
The current study has several strengths. We tried to minimize the potential risk of biases. The design and methodology of our study included dietary intake and PA assessments, allocation concealment, and blinding of subjects and investigators, while the previous studies were not accurate due to the lack of these items. Also, all subjects of our study were female and aged 20–50 years (homogeneous in physiological and hormonal conditions).
The current study has several limitations that should be interpreted with caution. We did not assess serum levels of vitamin E and the fatty acid content of red blood cells (RBC). Therefore, in future research, it is recommended to use this objective method to confirm adherence to dietary interventions. Also, we did not include oils with high SFAs such as palm oil found in the western diet. It does not seem ethical to consume unhealthy oils for 12 weeks in human clinical trials.