Kale is a leafy green vegetable belonging to the Brassica family, a group of vegetables that includes cabbage, collard greens, and Brussels sprouts. Half a cup of chopped, boiled kale has only 18 calories, 30% of the daily requirement (RDA) of Vitamin C, and enough Vitamin A and Vitamin K for the whole day. Vitamin A is required for the formation of rhodopsin, a photoreceptor pigment in the retina. Vitamin K controls the formation of coagulation factors in the liver.
The sulfur-containing phytonutrients in cabbage, broccoli and other cruciferous vegetables have been shown to reduce the occurrence of a wide variety of cancers. It is thought that the sulfurous compounds activate detoxifing enzymes in the liver that help neutralize substances that are potentially carcinogenic.
A study found that people who ate the most cruciferous vegetables had a 29% lower risk of bladder cancer than those eating the least of this family of vegetables. Another study found reduced intestinal polyps when the diet contained sulforaphane. Sulforaphane is an isothiocyanate that is present abundantly in broccoli and cauliflower.
Kale, broccoli, and cabbage should be in your menu if you are trying to lose weight while maintaining good nutrition.
 Zhao H, Lin J, Grossman HB, Hernandez LM, Dinney CP, Wu X. Dietary isothiocyanates, GSTM1, GSTT1, NAT2 polymorphisms and bladder cancer risk. Int J Cancer. 2007 May 15;120(10):2208-13. 2007. PMID:17290402.
 Hu R, Khor TO, Shen G, Jeong WS, Hebbar V, Chen C, Xu C, Reddy B, Chada K, Kong AN. Cancer chemoprevention of intestinal polyposis in ApcMin/+ mice by sulforaphane, a natural product derived from cruciferous vegetable. Carcinogenesis. 2006 May 4; 2006. PMID:16675473.