Material balance

Got up with a bit of a headache. Walked my dog around in my neighborhood first thing in the morning. She released herself and emptied her bowels. Without a garden to let her walk around, we have been taking her out several times a day since we moved here. Somehow she's got the habit of poo^^ almost every outing. So 3 to 4 times a day she has the pleasure of refreshing herself. We ran out of the plastic bags to put the stuff in, which we got from supermarket shopping, so my wife bought 180 bags the other day.
She eats one meal a day; 3 cups of dog food plus her favorites; a piece of sausage, cheese or ham as a topping. A question for me here is whether the input and output material balances out. She is not a big eater. So the amount she eats is, any way you look at it, far less than that she excretes. Perhaps water is the reason. She drinks plenty of water, which, together with good appetite, is hopefully a sign of good health. We can't care less how many times we have to pick up her droppings with a plastic bag.