Purpose: The modified Atkins diet (MAD) is a less restrictive treatment option than the ketogenic diet (KD) for intractable epilepsy and some metabolic conditions. Prolonged KD treatment may decrease bone mineralization and affect linear growth; however, long-term studies of MAD treatment are lacking. This study was designed to assess growth, body composition, and bone mass in children on MAD treatment for 24 months. Methods: Thirty-eight patients, mean age (SD) 6.1 years (4.8 years), 21 girls, with intractable epilepsy (n = 22), glucose transporter type 1 deficiency syndrome (n = 7), or pyruvate dehydrogenase complex deficiency (n = 9) were included. Body weight, height, body mass index (BMI), bone mass, and laboratory tests (calcium, phosphorus, magnesium, alkaline phosphatase, cholesterol, 25-hydroxyvitamin D, insulin-like growth factor-I and insulin-like growth factor binding protein 3) were assessed at baseline and after 24 months of MAD treatment. Results: Approximately 50% of the patients responded with more than 50% seizure reduction. Weight and height standard deviation score (SDS) were stable over 24 months, whereas median (minimum maximum) BMI SDS increased from 0.2 (-3.3 to 4.5) to 0.7 (-0.9 to 2.6), p amp;lt; 0.005. No effects were observed for bone mass (total body, lumbar spine and hip) or fat mass. Conclusions: The MAD was efficient in reducing seizures, and no negative effect was observed on longitudinal growth or bone mass after MAD treatment for 24 months. (C) 2019 Published by Elsevier Ltd on behalf of European Paediatric Neurology Society.