It depends on the individual's metabolism but it happens rather quickly for most women (within a couple of hours). Garlic "flavors" breast milk more than spicy food, although spices can alter the taste if a woman consumes a lot of them. Most experts agree that a woman does not have to abstain from eating anything she desires while nursing a baby that is older than 3-4 months UNLESS her baby develops a skin rash, has a gassy reaction to certain food, becomes mucusy, etc. Then stop eating the offending food.