Metabolic syndrome (MetS) is a complex condition influenced by aging, genetics, and lifestyle factors such as physical inactivity, poor nutrition, and obesity, contributing to its increasing global prevalence (1, 2). MetS shares many pathophysiological features with type 2 diabetes (T2DM), obesity, prediabetes, and non-alcoholic steatohepatitis (NASH), including insulin resistance, dyslipidemia, and chronic low-grade inflammation (3). Epidemiological studies estimated that the incidence of MetS will reach 53% by the year 2035 (4). The most widely used diagnostic criteria for MetS are provided by the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) and the International Diabetes Federation (IDF) (5, 6). These criteria include elevated fasting blood sugar (FBS), blood pressure (BP), triglycerides (TG), waist circumference (WC) (central obesity) and reduced high-density lipoprotein cholesterol (HDL-C) (7). Likewise, it is crucial to halt its growing prevalence using preventive strategies. In this context, Cumin (Cuminum cyminum L.) has been demonstrated to be effective in metabolic panel.

Cumin is a medicinal plant from the family Apiaceae, native to the Eastern Mediterranean and South Asia (8). The dried seeds of cumin are used as a culinary spice in many countries (9). Cumin seeds contain over 100 different chemicals, including fixed oil, volatile oils, essential fatty acids, protein, vitamins and minerals. Previous research has shown that this spice has anti-inflammatory, antioxidant, anti-diabetic, and immune-modulating activities (10, 11). Anti-inflammatory effects are mediated with downregulation of pro-inflammatory cytokines [e.g., tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6)] (12). In addition, bioactive compounds found in cumin have been shown to mitigate the oxidative stress by neutralizing free radicals (9, 13). Enhanced insulin secretion following cumin supplementation supports its insulin-sensitizing properties (14). Some studies also suggest that cumin may promote weight loss through increased adiponectin levels and reduced leptin resistance, which may suppress appetite and enhance energy expenditure (15, 16).

Several randomized controlled trials (RCTs) have investigated the effects of cumin supplementation on adults with metabolic abnormalities. However, most included trials focused on individuals with T2DM, overweight/obesity, prediabetes, or NASH, with only a limited number of studies specifically enrolling rigorously defined MetS patients (15, 17, 18). This discrepancy introduces indirectness and internal inconsistency between the stated research question, eligibility criteria, included populations, and conclusions.

Nonetheless, there is inconsistency among trials investigating the effects of cumin on components of MetS (19, 20). Samani and Farrokhi (21) administered 25 mg of cumin per day for individuals with MetS. This study was accompanied with significant improvement in term of glycemic state and lipid profile (TG and HDL-C). While, some other studies failed to show significant changes in term of FBS following cumin supplementation (15, 22). Similarly, Kazemipoor et al. (37) administered cumin for 12 weeks for obese subjects and illustrated a significant reduction in WC level. Whereas, other study failed to show positive effects for cumin regarding WC improvement in pre-diabetic patients. Also, none of these studies performed a Grading of Recommendations Assessment, Development and Evaluation (GRADE) assessment, making it impossible to comment on the quality of the obtained evidence. Third, none of these studies have focused on patients with MetS. Therefore, this study aims to systematically evaluate the impact of cumin supplementation on MetS components in adults with metabolic disorders through a meta-analysis of RCTs, while assessing the quality of evidence using the GRADE approach. By integrating these methodologies, this research seeks to provide comprehensive insights into cumin’s efficacy in managing metabolic disorders and identify areas for future investigation.

The current meta-analysis summarized the results of nine RCTs involving 531 participants. It demonstrated that cumin supplementation may exert beneficial effects on the management of metabolic syndrome. Subgroup analyses revealed that age, baseline health condition, intervention dosage, and duration were key sources of heterogeneity among the included studies. It is important to note that the subgroup findings (e.g., age >50 years, dose <100 mg/day, duration >8 weeks, T2DM) are exploratory and hypothesis-generating rather than definitive. Given the small number of studies per subgroup and persistent heterogeneity, these results should not be interpreted as prescriptive clinical recommendations. The observed trends in specific subgroups may suggest potential mechanisms or populations that could benefit more from cumin supplementation, but further high-quality trials are needed to confirm these findings. For instance, participants >50 years exhibited a greater reduction in FBS levels compared to younger individuals, possibly due to the increased prevalence of insulin resistance in older adults. This supports the hypothesis that cumin supplementation may exert more pronounced effects in populations with impaired glucose metabolism. Additionally, participants with T2DM showed significantly greater improvements in FBS, further reinforcing the relevance of Cuminum cyminum L. as a potential adjunctive therapy in this subgroup. Interestingly, a significant hypoglycemic effect was also observed at lower doses (<100 mg/day), suggesting that even minimal supplementation may yield metabolic benefits. Nonetheless, given the high heterogeneity in both subgroups, it is crucial to interpret these findings cautiously. These findings highlight the importance of considering participant characteristics and intervention parameters when interpreting the effects of cumin supplementation, and they underscore the need for more stratified analyses in future trials. This finding suggests that the bioactive compounds in cumin may exert their effects through modulation of cellular signaling pathways at low concentrations, potentially via mechanisms such as enhanced insulin sensitivity. Nonetheless, given the high heterogeneity in both subgroups, it is crucial to interpret these findings cautiously. The antidiabetic effects of cumin are attributed to its aldehyde compounds, especially cumin aldehyde, which can inhibit alpha-glucosidase and thus reduce glucose absorption in the small intestine (38, 39). In addition, cumin aldehyde can inhibit the function of aldose reductase, which increases the production of reactive oxygen species (ROS) in tissues (39). Through its antioxidant compounds, cumin reduces serum levels of tumor necrosis factor-α, a pro-inflammatory cytokine that inhibits insulin signaling and its biological actions, which can improve insulin sensitivity (40, 41). Notably, Jafari et al. (17) found that a 100 mg dosage of cumin resulted in a significantly greater reduction of FBS compared to a 50 mg dosage. However, both short- and long-term treatment showed significant effect on FBS. Likewise, it is important to pay attention to doses of cumin supplementation irrespective of treatment duration. Literature review showed supportive studies in line with our findings to improve components of MetS in patients with T2DM (33, 36, 42). While, several studies reported contradictory results in this regard (20, 22). It may be attributed to various cumin preparation, dosage, study population and severity of health condition.

In addition, cumin had ameliorative effects on TG level too. Moreover, subgroup analysis showed significant reduction in older adults (>50 years old) as expected. Due to significant metabolic changes associated with aging, older adults often need more carefully adjusted and targeted therapeutic interventions to achieve desired treatment effects. Short-term treatment demonstrated beneficial effects in reducing TG levels. However, this improvement may reflect transient metabolic adaptation, as long-term interventions could lead to different outcomes. Bioactive compounds found in cumin may activate the peroxisome proliferator-activated receptors (PPARs) pathways. PPAR-α activation promotes fatty acid oxidation while suppressing TG synthesis in hepatocytes, contributing to reduced hepatic lipid accumulation (15, 43). Also, T2DM patients may experience some degree of dyslipidemia. In that case, the lipid-lowering effect of cumin may be pronounced in T2DM patients based on subgroup analysis. In this context, 10-week administration of cumin essential oil improved lipid profile except total cholesterol level in prediabetes patients (17).

Furthermore, the present study demonstrated that cumin increased HDL-C level significantly. However, this significant effect was most pronounced at lower doses and with long-term intervention, suggesting a dose- and duration-dependent interaction in cumin’s modulation of lipid metabolism (21). The HDL-C raising effect of cumin, especially at lower doses over longer periods, is indicating that formation of HDL-C through LCAT pathway require longer periods of metabolic adjustment. Cumin is rich in polyphenols, which have antioxidant properties. These properties of cumin may protect HDL-C from oxidation (19, 21). A possible mechanism for the hypocholesterolemic effects of cumin may be related to the stimulation of cholesterol 7 alpha hydroxylase in the liver, which converts cholesterol to bile acids. And the presence of saponin in cumin, which interferes with the liver-intestinal circulation of cholesterol, reduces its absorption. Also, these results may be explained by the possible role of cumin in regulating the action of β-hydroxy-beta-methylglutaryl-CoA reductase, which is the main enzyme in cholesterol synthesis (44, 45). In addition, cumin has a significant amount of certain phytosterols that reduce the absorption of cholesterol (46). Finally, the antioxidant content of cumin, e.g., vitamin C, carotenoids, vitamin E, and polyphenols can moderate LDL oxidation and reduce LDL-C levels (21, 47). Consistent with our finding, Jafarnejad et al. (42) demonstrated that cumin significantly affected the HDL-C level in overweight and T2DM patients.

On the other hand, cumin supplementation was associated with a significant reduction in WC, indicating its potential in addressing central obesity. As mentioned previously, the antioxidant and anti-inflammatory properties of cumin play a key role in triggering the reduction in WC, likely by mitigating oxidative stress and inflammation, which are major contributors to abdominal fat accumulation (40).

It is important to highlight that while this meta-analysis demonstrates the potential of cumin supplementation in improving metabolic outcomes, substantial heterogeneity was observed across the included studies. Therefore, the interpretation of subgroup findings should remain cautious, and the results should be considered exploratory rather than definitive. This variability in results may be attributed to both methodological and biological factors. Notably, differences in cumin formulations and dosages appear to be key contributors to this heterogeneity. To address this issue, a subgroup analysis was conducted. However, it is recommended that future studies be performed with larger, more homogeneous populations to enhance the reliability and generalizability of the findings. Therefore, future RCTs employing varied dosages and assessment approaches across diverse regions are needed to strengthen and broaden the evidence base.

The quality of obtained evidence for outcomes was moderate to high. Although, there was a considerable risk of bias in some included studies, both high and low-qualified studies approved beneficial effects of cumin. Furthermore, the use of the GRADE approach in our study allowed for a more rigorous evaluation of the evidence quality, which evidence rated moderate to high. Registered protocol in PROSPERO, adherence to PRISMA guidelines, performing comprehensive subgroup analyses, low risk of publication bias, and grade approach were the strengths of our study. The novelty of this study lies in its focused examination of the effects of cumin specifically within MetS populations, distinguishing it from prior research. Our meta-analysis study has limitations that should be noted. First, due to the limited number of studies, subgroup analysis was not possible for WC. Secondly, in most of the included studies, the duration of supplement use was short. In addition, most of the included studies had incomplete outcome data. Therefore, further long-term clinical trials focusing on different forms of cumin are needed to clarify this issue. All studies included in this review were conducted in Iran, which may limit the generalizability of the findings. Variations in dietary habits, genetic backgrounds, and clinical management of metabolic syndrome within the Iranian population could affect the observed effects of Cuminum cyminum L. supplementation and may not reflect outcomes in other populations. Therefore, this geographical focus is considered a limitation of our study. To enhance the external validity of these results, future randomized controlled trials from diverse regions, such as Asia, Europe, and North America, are needed to evaluate the cross-cultural applicability of the findings. Due to the very limited number of studies reporting BP, this core component of MetS could not be included in the meta-analysis, which limits the comprehensiveness of the findings. In addition, smaller number of studies were included for each outcome, which suggests that funnel plots and Begg/Egger tests may present insufficient power. Accordingly, the findings should be interpreted with cation.

Cumin has improved and had favorable effects on components of MetS. Long-term (>8 weeks) supplementation cumin (<100 mg/day) in the age of more than 50 years is a more efficacious approach in this review. According to the present study, cumin can be used as an effective adjuvant agent, particularly for patients with T2DM. Due to the limitations of our research, it is essential to interpret the results with caution.