- Part A only: Any subject who by history regularly consumes a large quantity of foods rich in vitamin K will be excluded unless he/she restricts the vitamin K intake for at least one week prior to the first dose of warfarin. For study purposes, large quantities of vitamin K-containing food will be defined as 10 or more portions per week of the following: kale, spinach, turnip greens, cauliflower, chick peas, brussels sprouts, green tea, liver, soybean oil and soy protein products.