As we all know, sweet potato is rich in nutrition. However, what's more valuable is, among the 20 kinds of anti-cancer vegetables which are released recently by the Japanese National Cancer Research Center, sweet potato ranks the first.

Cancer cells come from the epithelial cells of human body, while the sweet potato is rich in starch, carotenes as well as ten kinds of trace elements such as potassium, iron and so on. These nutrients have a variety of effects to human body, such as protecting the structural integrity of human epithelial cells, inhibiting the activity of the virus, blocking the formation of nitrosamines in the gastrointestinal tract, eliminating the toxicity of mercury, cadmium, arsenic in the foods or environment, as well as blocking the carcinogenic process of the toxic metals. As a result, sweet potato is regarded by the experts as the health food which contains the most balanced nutrition.

What's more, sweet potato contains a unique substance called as DHEA (dehydroepiandrosterone), which is a kind of steroid hormones secreted by the adrenal gland and is similar to the androgen. This substance not only can prevent cancer, but also can prolong human life. A lot of data has confirmed that DHEA can effectively inhibit the occurrence of breast cancer and colon cancer.

However, sweet potato contains some gasified enzyme. If you eat too much of it, it is likely to cause heartburn, acid regurgitation, abdominal distension, belching and other symptoms. As a result, you should pay attention not to eat too much sweet potatoes. 150 grams every time is appropriate. In addition, people who suffer from indigestion should also be careful when eating sweet potatoes. The shortcoming of sweet potato is the lack of protein and fat. As a result, it is best to eat sweet potato together with other foods which are rich in protein and fat.

Last but not the least, you should pay attention not to eat the sweet potato with black spots on the surface. Because if the sweet potato appears brown or black on the surface, this means it has been contaminated by the alternaria brassicicola. The toxins discharged by alternaria brassicicola contain sweet potato ketone alcohol, which will make the sweet potato become bitter and hard, and bring harms to human liver. The biological activity of this toxin can not be destroyed no matter by boiling and steaming with water, or roasting with fire. As a result, eating the sweet potato with black spots can cause poisoning.