(1) Background: Considering the limited amount of available data on the diet quality of children, adolescents, and young adults with an intellectual disability (ID) in Poland, as well as the higher incidence of nutritional disorders among people with ID in comparison to the general population, a study was conducted to assess the quality of diet in community-dwelling young individuals with ID. (2) Methods: A multiple-case study was carried out to obtain data on anthropometric parameters and food records over a three-day observation period for 18 subjects with ID. The nutritional value of the products and dishes consumed by the subjects was calculated using the commercial computer program Kcalmar.pro (Hermax, Poland), which contains the Polish database of the nutritional value of food products and dishes. The results presented here are those of a pilot study of a wider research project. (3) Results: The study group consisted of seven women (38.9%) and 11 men (61.1%) with an average age of 12.94 years (range 4.00–22.00) and an average BMI of 25.2 (range 14.5–35.4). The obtained results confirmed the suboptimal pattern of nutrition in children and adolescents with ID. Regarding energy intake and dietary macronutrients, only in 27.8% of cases, energy intake exceeded the Estimated Energy Requirement corresponding to age, sex, body weight, and height. Most of the respondents were characterized by correct intake of proteins, fats, and carbohydrates, and 83.3% showed excessive intake of saturated fatty acids. Excessive intake of vitamins B1, B2, and B6 was observed in all subjects, and that of vitamins B3 (niacin), B12, A, and C in the vast majority of subjects, while deficiency of vitamin D was observed in all individuals and folic acid in 22.2% of individuals. Excessive intake of minerals, such as sodium, phosphorus, and magnesium was noted among most of the respondents, while the intake of calcium and iodine was found to be insufficient. Compared to people with less severe ID (grades 1 and 2), people with grade 3 ID showed significantly lower intake/reference fulfillment of dietary components such as vitamin B6, potassium, phosphorus, iron, copper, iodine, magnesium, and zinc. No significant differences were noted in the nutritional reference fulfillment for various nutrients among the groups distinguished by sex, nutritional status, or the cause of ID. (4) Conclusion: Health supervision guidelines proposed for persons with ID should take into account the dietary practices of the families caring for them, with an emphasis on the prevention and correction of irregularities that may reduce the effectiveness of rehabilitation and deteriorate the health of the affected people. Caregivers/parents of each person with ID who took part in the study were given individualized dietary advice aimed at correcting the dietary abnormalities.
