Food paste appears as a cafeteria tray with a blob of pink paste on it. It replaced all forms of food at Suffolk County charter school as an experiment to help fund the school through a program called the Nutritional Alternate Paste Program (NAPP), developed by Vault-Tec in conjunction with the federal government. The paste was designed to provide complete nutrition and have a shelf life of over 100 years.
Holotapes found in the school suggest that the paste is completely devoid of flavor, turns skin pink with regular consumption, and has psychological effects such as irritability.
The area that this consumable is found has a unique population of pink feral ghouls, which supports the observation of the paste turning the skin pink.
One can find dead raiders with a letter on them regarding the paste as a random encounter. This note mentions that one of the raiders has become addicted to the food paste, and that they are having an intervention. This suggests that the food paste has some addictive qualities.
No matter how much paste is consumed by the Sole Survivor, they will never experience any of the side effects of food paste consumption.
The following is based on unverified behind the scenes information and has not been confirmed by canon sources.
The food paste as a whole is a reference to Pink Slime, a food additive consisting of low-fat meat which was ground into a paste. It's particularly infamous after being widely used as a meal alternative in American school lunches during 2012, which resulted in major controversy.
End of information based on unverified behind the scenes information.
↑Vault Dwellers Survival Guide, page 384 - "The student base of this school consisted mostly of lower-income and disadvantaged students. These children were lucky enough to be chosen for trials of a new food substitute paste developed by Vault-Tec in conjunction with the U.S. government. The paste was intented to provide all necessary nutrition and have a shelf life of over 100 years.