Clotting is a protective mechanism of our body, which the blood cells clump together to prevent excessive bleeding. But sometimes, spontaneous and unnatural clotting can cause strokes and heart attacks. That’s why doctors often prescribe chemical blood thinners to people with underlying heart problems like valve disease or irregular heartbeats. Although they are not a substitute for the thinners your doctor prescribes, some natural ingredients can help prevent clots.
Turmeric: Curcumin is a potent ingredient in turmeric that has a wide range of health benefits, one of which is its anticoagulant effect. Evidence suggests that turmeric has anti clotting properties and consuming it daily will help protect against thrombosis. 
Garlic: Studies say ingestion of fresh or powdered garlic can stop aggregation of platelets and preventing the formation of blood clots in the body.  For best results, it should be had raw than cooked.
Onion: The world’s most widely-used ingredient the onion is known to have antithrombotic properties. Eating raw onions in moderation keeps the blood light and flowing. 
Ginger: Another ingredient with a possible anticoagulant effect is ginger. Preliminary studies suggest that ginger can help in preventing clotting episodes and resultant strokes. 
Cinnamon: This fragrant spice has blood thinning effects, if used in moderation. Coumarin, an important ingredient in cinnamon is a powerful anticoagulant. But too much of it could damage the liver adversely.