Consuming large amounts of kale, spinach, Brussels sprouts and parsley is not advised during warfarin treatment, states WebMD. Because they contain high levels of vitamin K, these foods decrease the effectiveness of warfarin. Avocados, alcohol, margarine, mayonnaise and grapefruit juice should also be avoided, states Indiana Hemophilia & Thrombosis Center.
It is important for patients taking warfarin to be aware of foods that are high in vitamin K and maintain a consistent vitamin K intake, according to Indiana Hemophilia & Thrombosis Center. Several lifestyle changes may influence the levels of vitamin K in the body, including increasing vegetable intake in an effort to lose weight; being sick and unable to eat solid food; being on a limited diet after surgery or illness; travelling to unfamiliar areas; and increasing intake of lentils, beans or dried peas. It is best for patients on warfarin to notify their physicians of any major dietary changes or before starting new vitamins or supplements, states WebMD.
Vitamin K is an important nutrient in the body that produces blood clotting factors, according to Indiana Hemophilia & Thrombosis Center. Warfarin slows the blood clotting process by interfering with the activity of vitamin K. This is why increasing vitamin K consumption while taking warfarin works against the medication and decreases its effectiveness.