Which food item should be avoided or limited in a patient taking warfarin?

• A. Meat
• B. Bread
• C. Leafy green salads
• D. Fish

Answer: (C)

The main idea is that warfarin's effect is highly sensitive to vitamin K intake. Warfarin works by inhibiting the enzyme that activates vitamin K, which is needed to form the clotting factors II, VII, IX, and X. When you eat foods rich in vitamin K, like leafy green vegetables, the vitamin K can counteract warfarin’s anticoagulant effect, lowering INR and potentially reducing protection against clots. Conversely, very low or inconsistent vitamin K intake can increase warfarin’s effect and raise bleeding risk. Because leafy greens are especially high in vitamin K, they have the strongest potential to alter warfarin control, so they should be avoided or kept at a consistent level in a patient taking warfarin. Foods such as meat, bread, and fish don’t have the same impact on vitamin K and thus don’t require the same avoidance, though overall diet should be stable and INR regularly monitored.