The fully ripe banana produces a substance called TNF which has the ability to combat abnormal cells. As the banana ripens, it develops dark spots or patches on the skin. The more dark patches it has, the higher will be its' immunity enhancement quality . Hence the Japanese love bananas for a good reason. According to a Japanese scientific research, banana contains TNF which has anti-cancer properties. · The degree of anti-cancer effect corresponds to the degree of ripeness of the fruit, i.e. the riper the banana, the better the anti-cancer quality.. In an animal experiment carried out by a professor in Tokyo U comparing the various health benefits of different fruits, using banana, grape, apple, water melon, pineapple, pear and persimmon, it was found that banana gave the best results. It increased the number of white blood cells, enhanced the immunity of the body and produced anti-cancer substance TNF. The recommendation is to eat 1 to 2 banana a day to increase your body immunity to diseases like cold, flu and others. According to the Japanese professor, yellow skin bananas with dark spots on it are 8 times more effective in enhancing the property of white blood cells than the green skin version.