It is a common observation that food is tasteless when we have a cold. Why is that so?
What is the cause of inability to taste when we have a cold? Are the nose and ability to taste connected?
This German review supports common wisdom that the sense of taste is predominantly informed by the sense of smell. For instance, common advice to children taking "nasty" tasting medicines is to plug one's nose. Any condition that blocks olfaction, such as sinusitis from flu or other sinus infections, or blocking nasal airflow, will decrease or block olfaction and as a result, the majority of taste.
There are many factors that contribute to the flavor of food - the five "traditional" tastes (sweet, sour, bitter, salty, umami), smell, texture, spiciness, "coolness" (like peppermint), temperature, etc. Smell and taste are detected in similar ways, by chemoreceptors expressed in taste pores by specialized cells of the lingual epithelium (tongue), and in the nose by the olfactory epithelium. Both are affected by upper respiratory tract infections like colds and the flu, leading to diminished senses of taste and smell, and a corresponding reduction in the overall flavor of food.