Wouldn't you know it, they now have research showing that you can cause more harm to your teeth brushing after you eat than if you would wait?!
Here's the scoop....if you brush too closely after eating food, the enamel (the layer that protects your skin and you can NOT replace once lost) becomes weak. This is especially true with foods that have higher levels of acid. When your enamel is in a weakened state, your brushing can actually cause you to lose enamel. This level is practically untraceable, but if you brush after every time you eat, every day, every week, every month, over years...that's a lot of enamel!
Best advice, brush twice a day, but make sure you give yourself some time after you have finished eating so that your enamel isn't as soft.