Small changes in diet do not affect warfarin control, but significant changes can. If your patient plans to go on a weight loss diet make sure they discuss this with their doctor first.
Warfarin works by blocking the action of vitamin K. Green vegetables contain vitamin K and therefore a diet high in green vegetables can alter warfarin control.
Recent studies have shown that people need to eat a large amount of vegetables to have a significant effect on warfarin control. Spinach and broccoli have high levels of vitamin K. One study showed that people on warfarin needed to regularly eat approximately half a kilogram of broccoli or spinach daily to have a significant effect on their warfarin control.
Patients should have a normal balanced diet including some green vegetables. They should not stop vegetables completely, but they should avoid large variation in their diet.
People on warfarin should limit alcohol intake to one or two glasses of wine or beer each day. Excessive alcohol and especially binge drinking can damage the liver and increase the anticoagulant effect of warfarin. Alcohol can also inflame the lining of the stomach and increase the risk of bleeding.