Carrots are rich in poly-acetylene antioxidant, falcarinol. Research study conducted by scientists at University of Newcastle on laboratory animals has found that falcarinol in carrots may help fight against cancers by destroying pre-cancerous cells in the tumors.
Potatoes are very good natural sources of both soluble and insoluble fiber. The dietary fiber in them increases the bulk of the stool, thus, it helps prevent constipation, decrease absorption of dietary cholesterol and thereby, lower plasma LDL cholesterol. Additionally, its rich fiber content also helps protect from colon polyps and cancer.
Fresh kohlrabi stem is rich source of vitamin-C; provides 62 mg per 100 g weight that is about 102% of RDA. Vitamin C (ascorbic acid) is a water-soluble vitamin, and powerful anti-oxidant. It helps the human body maintain healthy connective tissue, teeth, and gum. Its anti-oxidant property helps the human body protect from diseases and cancers by scavenging harmful free radicals from the body.
Data taken from http://www.nutrition-and-you.com/