Is Hunger Due to Scarcity or Waste?

I hear people say that we need population control since there's not enough food to feed people. Oh really? One day, in our office cafeteria, I saw a customer grab a sandwich wrapped in plastic. When she found out from the cashier that it had mustard in it, she didn't want it anymore. So the cashier threw it in the garbage can. I was stunned by this waste. It also reminded me of my college days, when I worked in a buffet restaurant at night. When dinner was over, any remaining food from the buffet was simply thrown out. All of this food could have been donated instead to food banks to feed the needy. This made me wonder, "Is the problem of hunger due to the scarcity of food, or is it simply due to the waste of food?"