The food in prison is generally not of the gourmet variety. The menus are set by a licensed and registered nutritionist using standardized tables for balanced meals. They provide about 2200 calories per day with a mix of carbohydrates, proteins and fats. The main complaint is that the food is bland and lacks seasoning but it will fill them up. Commissary items are used to supplement the food they receive in the chow hall.
https://www.inmateaid.com/ask-the-inmate/how-is-the-food-my-brother-is-eating-is-it-good#answer
Accepted Answer Date Created: November 29,2015