Abstract

Purpose Since obesity is a risk factor for various diseases and is associated with increased oxidative stress conditions, some herbs are considered to be effective in reducing obesity and its complications. Methods This secondary analysis investigates the effect of Nigella sativa (N.S) oil supplement on total antioxidant capacity (TAC) and malondialdehyde (MDA) levels in obese/overweight women. Obese and overweight healthy women were randomized to receive 2,000 mg/d of N.S supplement and placebo. The intervention periods lasted 8 weeks and were separated by a 4-week washout period. Also, each participant was given an iso-calorie diet. Baseline characteristics and TAC and MDA levels were measured. Pkcross analysis was performed for statistical analysis using Stata software. Also, Cohen’s d was estimated as effect size for all results to assess the magnitude of the effects. Results 39 women completed the study. N.S oil supplementation at a dose of 2000 mg/d significantly increased serum TAC (P effect = 0.017, Cohen’s d = 1.81) and reduced serum MDA (P effect < 0/001, Cohen’s d =  − 0.32). Conclusion Based on our findings taking N.S supplementation for 8 weeks can improve antioxidant conditions in obese and overweight adults. However, more studies with a larger population and the presence of both genders need to be done to confirm the results.