Actually that's a great way to train a dog to be food aggressive, seeing as you keep going up and randomly taking their food. Dogs that guard stuff do so because they are afraid you are going to take it, doing just that isn't going to help matters. Instead make you near their bowl a good thing, drop some treats in while they are eating, once they are comfortable with that, take it away for a milisecond and drop something really yummy in and give it right back, pretty quick you'll have a dog who loves people by their stuff, not one who thinks people are out to steal it. I'll never understand why people are so dead set on messing with dogs while they eat anyways, I expect my dogs to leave me alone while I eat and they get the same respect.