Why does food taste so bad when you have a flu?

Introduction: 

Ever had the flu? Feels bad right? Right now my country, everyone's having the flu. I had the flu at the worse period of time, Chinese New Year! What's the point of eating food if you can't taste it! It'll just make you fat! But sometimes, I use this trick when I was young to eat veggies my Mom forced me to eat. I pinch my nose and eat it, I can't taste the veggie taste! So? What is happening to our nose and mouth? Why does food not taste good when you have the flu?

Explanation:

Firstly, ever seen this picture before?

Yes, That's right, it's WRONG. The tongue map or taste map is a common misconception that different part of the tongue is exclusively responsible for different basic tastes. It is illustrated with a schematic map of the tongue, with certain parts of the tongue labeled for each taste. Although widely taught in schools, this was scientifically disproven by later research; all taste sensations come from all regions of the tongue, although parts may be more sensitive to certain flavors. Although the diagram is wrong, there is also something right, the human tongue can distinguish only among five distinct qualities of taste, which is sweet, sour, bitter, salty and umami(the flavor of glutamates(A salt or ester of glutamic acid)). So apart from those, we cannot taste anything else! When we pinch our nose, we can't tell apart an apple from a potato!

What's really going on?

Well, the nose can distinguish among hundreds of substances, even in small quantities. When we exhale, our sense of smell contributes to the flavour! When you are sick with something like the flu, it can make it difficult to smell things. Swollen sinuses or a blocked nose can be the cause of this for you. So you can't use your nose to "Taste" the food. That's why it taste bad!

*Funfact* The word for the sense of smell is Olfaction.