According to Japanese Scientific Research, full ripe banana with dark patches on yellow skin produces a substance called TNF (Tumor Necrosis Factor) which has the ability to combat abnormal cells. The more dark patches it has the higher will be its immunity enhancement quality . . . the anti-cancer quality. Yellow skin banana with dark spots is 8x more effective in enhancing the property of white blood cells than green skins. 1-2 banana/s a day increases immunity. Shared by NancyJo Andrews.