Waste is a homophone of waist. Waste means refers to things discarded because they are no longer useful. A waist refers to the part of the human body below the ribs and above the hip. "Food gonig to waste" means food that gets thrown out. "Food going to waist" means food that makes someone gain extra weight, which can be seen around the person's waist. This joke is a play on the word "waist" and its homophone "waste".
Some people don ' t like food going to waist .