I think that Lab's are prone to ear infections. I also think that it may be heretitary. I had a lab that had terrible ear infections. We used ear drops and cleaned out her ears once a week and the infections comtinued. Her mother and brothers also had the same problem. The lab I have now does not have the problem, but I have been very careful to keep her ears clean and watch for infections. She did get a problem in one ear, I put drops in the ear and it cleared right up. We also have noticed that if a lab spends alot of time in the water that seems to make their ears worse. Labs look to swim so after a swim clean out their ears really good. I really don't know what the connection would be with the food that they eat having to do with ear infections. It doesn't make sense to me.
Go to your vet and get some ear drops and cleaning solution for the ears and have it on hand and use it. That is the only thing I know of that will help. Good Luck Julie