When you are on an airplane, the cabin is pressurized. This allows you to breathe, as the air thousands of feet in the sky is not as dense as the air on the ground. When the cabin is pressurized, that means the things inside of it are pressurized as well. You are one of those things. This directly affects your senses, especially smell and taste. The low pressure can reduce taste bud sensitivity to sweet and salty food by around 30%.