A systematic review and meta-analysis was conducted to determine the effects of prebiotics or synbiotics on blood biomarkers of obesity, depression, and anxiety (including: ACTH [adrenocorticotropic hormone], cortisol, leptin, ghrelin, TSH [thyroid-stimulating hormone], PTH [parathyroid hormone], vitamin D, BDNF [brain-derived neurotrophic factor], and PCR [polymerase chain reaction]) in individuals with overweight or obesity.
The results revealed a significant effect of smoking on BMI, but a lack of significant association between BDNFVal66Met polymorphism and overweight or obesity, and no significant association between BDNF Val66Met and BMI changes over time.