Commonly called black seed, NS is a medicinal herb cultivated mainly in the Middle East and South West Asia. It is said to have therapeutic effects against diabetes, hypercholesterolemia, hypertension, gastrointestinal disorders, inflammation, and even cancer.
However, these results have been controversial, with some studies noting a significant decrease in obesity after NS supplementation, and others observing no such change.
There has also been no meta-analysis available on NS' impact on obesity indices. As such, researchers at Iran's Tehran University of Medical Sciences and Shahid Beheshti University of Medical Sciences conducted a systematic review of RCTs on NS' effects on body weight, BMI and waist circumference.
They used 13 RCTs published up to January 2018, with a total of 875 participants (64% male, 36% female). In 10 of the studies, NS supplementation was shown to help lower body weight significantly, compared to a placebo.
In 11 of the trials, BMI was also reduced following NS supplementation, but in five of the studies, no significant reduction was observed in waist circumference.
The researchers wrote that they had tested for publication bias and found none, and that none of the individual studies significantly influenced their observations. They also acknowledged some of the meta-analysis' limitations, such as the different types of NS supplementation in varying doses that were used in the studies reviewed.
At the same time, obesity indices were measured using methods that differed from study to study, and subjects displayed different health statuses.
In addition, the study duration in most of the RCTs reviewed tended to be short, necessitating future clinical trials with longer intervention periods. The researchers also did not control for certain important confounders, which may explain the variance in results.
They concluded: "This meta-analysis showed a signiﬁcant eﬀect of NS supplementation on body weight and BMI, but not on waist circumference, in adults.
“Additional RCTs with longer intervention periods are needed to shed light on this issue."
Source: Complementary Therapies in Medicine
"Eﬀect of Nigella sativa supplementation on obesity indices: A systematic review and meta-analysis of randomized controlled trial"
Authors: Seyed Mohammad Mousavi, et al.