As long as your water chemistry is not detrimentally effected feed them all they want, they will be healthier for it, and they do get to a point where they are full. When I go fishing , during times when food is readily available for them and the fish are in a full blown feeding frenzy for as long as the excess food is available the fish are all very strong, have obese bellys and healthy and are very stout and solid. When food sources are not as readily available the fish are thin, lethargic( not strong fighting ) and also show signs of disease( leasions, open sores, parasites, etc..) So I apply the same to my fish, keeping them well fed and it seems to work really well.