When should I brush my teeth?: Dr Pratish Dholakia, Dentist
Ideally you want to leave at least twenty minutes after you've had a meal. You can brush your teeth before a meal, that will have no consequence there.
If you brush your teeth immediately after a meal, the PH of your mouth has altered when you have a meal, so you're brushing them when they're at a weak point there.
So leave it at least 20 minutes to half an hour between eating and brushing your teeth.