Yam is good. Yam contains many trace elements, especially potassium. There are few kinds and quantities of vitamins, including vitamin B 12, vitamin K, vitamin P and vitamin D, and almost no carotene. The leaves of Chinese yam are excellent sources of carotene, calcium, iron and vitamin C. Yam contains starch glucoamylase, amylase and other digestive enzymes. In particular, it contains starch glucoamylase, which can decompose starch three times as much as radish. Eating it when you have abdominal distension can promote digestion and eliminate discomfort. Yam contains no fat, and mucin can prevent fat deposition in cardiovascular system and prevent premature arteriosclerosis.