The gluten-free diet (GFD) requires special attention from nutritionists due to the potential risk of nutrient deficiencies in its users. This risk may be greater when this type of nutrition is implemented in prisons due to the limited possibilities of external control, a low catering budget for meals, and insufficiently defined recommendations regulating nutrition for prisoners. The aim of the present study was to assess the nutritional value of GFD and regular diet meals served in some Polish prisons and to compare the values to the dietary reference intake (DRI) standards. Using a specialized computer program, 7-day menus of both types of diet provided in 10 prisons were analyzed. The percentage coverage of the DRI was calculated based on the recommendations of the Polish National Food and Nutrition Institute. GFD was characterized by lower average contents of energy and 11 out of 14 essential nutrients, i.e., protein, carbohydrates, dietary fiber, starch, ash, sodium, calcium, iron, zinc, folate, and vitamin B12. The average content of phosphorus, niacin, and riboflavin in the gluten-free diet was higher than that in the regular diet. It was shown that the meals in GFD and the regular diet did not provide the recommended amounts of calcium (38 and 44% DRI, respectively), vitamin D (29 and 30% DRI), vitamin C (86 and 76% DRI), and folate (51 and 56% DRI). In turn, the supply of sodium, phosphorus, copper, and vitamins A and B6 substantially exceeded the recommended levels. The results indicate a need for greater quality control of GFD meals served in catering facilities. It is also necessary to develop legal provisions that will regulate more specifically the nutrition for prisoners in terms of an adequate supply of minerals and vitamins.