The effect of probiotics on human health has been studied in a wide range of conditions, and many studies focused on gastrointestinal conditions, atopic eczema, allergies, respiratory tract infections, obesity, metabolic disease/type 2 diabetes, cardiovascular, cognitive, and mental diseases, bone health, nonalcoholic fatty liver disease (NAFLD) and hepatic encephalopathy, tumor necrosis factor (TNF-α), autism, burn wounds, and gynecological diseases. The gene discussed is TNF; the disease is obesity due to melanocortin 4 receptor deficiency.