What is the reason for avoiding some green vegetables such as broccoli?

Many green vegetables contain Vitamin K. Vitamin K is important for blood to clot. Coumadin¬Æ/warfarin works to keep blood from clotting and high amounts of vitamin K might work against Coumadin¬Æ/warfarin. Green leafy vegetables like broccoli contain the highest amounts of vitamin K. A list of other foods containing vitamin K is below. It is also important to be aware that some multivitamins contain vitamin K. The most important thing to remember is to eat what you normally eat and not make any major changes in your diet, vitamins or begin a weight loss plan without consulting a doctor. 

Foods high in vitamin K: Vegetables, such as: Broccoli, Cabbage, Brussels sprouts, Green onions Leafy greens, such as: Lettuce, Spinach, Turnip, collard, and mustard greens, Parsley, Kale  Meats, such as: Beef liver, Pork liver  Other: Mayonnaise, Margarine, Canola oil, Soybean oil, Vitamins.