LAUSR

To assess the effect of Nigella sativa (N.S) oil supplements on CVD risk factors in a crossover design for the first time. Obese and overweight healthy women were randomized to receive N.S oil (2000 mg/day) and placebo. This intervention period lasted for 8 weeks and separated by a 4-week washout period. An iso-caloric diet was given to every individual throughout the study. Blood pressure, lipid profile, atherogenic indices and liver enzymes were measured. Pkcross procedure was performed for statistical analyses using Stata software. Cohen’s d was estimated as effect size for all outcomes to measure the magnitude of the effects. Thirty-nine participants completed the study. Capsules of N.S increased serum high-density lipoprotein cholesterol (Cohen’s d = 0.47, P = 0.009), reduced low-density lipoprotein cholesterol (Cohen’s d = − 0.33, P = 0.031), reduced TC/HDL-C ratio (as an atherogenic index, Cohen’s d = − 0.9, P < 0.001), reduced serum glutamic-oxaloacetic transaminase (Cohen’s d = 0− 0.5, P = 0.038) and reduced systolic blood pressure (Cohen’s d = − 0.4, P < 0.001). There was no effect on diastolic blood pressure measures (P = 0.96). The overall improvements in cardiovascular disease (CVD) risk factors showed beneficial effects of N.S supplements among adults with obesity to prevent possible cardiovascular diseases. More studies with different designs and in other populations are suggested to clarify the exact effects of N.S as a complementary therapy for modulating CVD risk factors in individuals with overweight and obesity. Iranian Registry of Clinical Trials, IRCT20180528039884N1, Registered on February 15th, 2019.