OBJECTIVE: The aim of this study was to evaluate the macronutrient and micronutrient intake and status in youth with type 1 diabetes mellitus (T1DM) following the consumption of a low-carbohydrate diet (LCD). RESEARCH METHODS AND PROCEDURES: In a prospective intervention clinical trial, adolescents with T1DM using a continuous glucose monitoring device were enrolled. Following a cooking workshop, each participant received a personalized diet regime based on LCD (50-80 g carbohydrate/day). A Food Frequency Questionnaire was administered, and laboratory tests were taken before and 6 months following the intervention. Twenty participants were enrolled. RESULTS: The median age was 17 years (15; 19), and the median diabetes duration was 10 years (8; 12). During the six-months intervention, carbohydrate intake decreased from 266 g (204; 316) to 87 g (68; 95) (p = 0.004). Energy intake, the energy percent from ultra-processed food, and fiber intake decreased (p = 0.001, p = 0.024, and p < 0.0001, respectively). These changes were accompanied by declines in BMI z-score (p = 0.019) and waist-circumference percentile (p = 0.007). Improvement was observed in the median HbA1c from 8.1% (7.5; 9.4) to 7.7% (6.9; 8.2) (p = 0.021). Significant declines below the DRI were shown in median intake levels of iron, calcium, vitamin B1, and folate. CONCLUSIONS: The LCD lowered ultra-processed food consumption, BMI z-scores and the indices of central obesity. However, LCDs require close nutritional monitoring due to the possibility of nutrient deficiencies.