Intensive Dietary and Activity Counselling (IDAC) study: a randomised trial following infants genetically susceptible to type 1 diabetes to prevent β-cell dysfunction and islet autoimmunity - a study protocol.

introductionType 1 diabetes is a chronic autoimmune disease, preceded by the presence of islet autoantibodies, a preclinical state defined as islet autoimmunity. Several environmental exposures have been associated with the initiation of islet autoimmunity but the triggers remain largely unknown. Rapid growth and weight gain during childhood are some of the exposures that have been proposed to promote islet autoimmunity. A high intake of protein and animal milks in early childhood is consistently associated with increased later obesity. Growth during early childhood is directly related to dietary intake and especially protein intake and this association has been linked to increased risk of islet autoimmunity and type 1 diabetes. The Intensive Dietary and Activity Counselling (IDAC) study aims to determine whether a healthy lifestyle counselling from age 3 months to age 2 years improves β-cell health in children with increased risk for islet autoimmunity. METHODS AND ANALYSIS: The IDAC study is a randomised trial (1:1 allocation) with two parallel groups, aiming to enrol 1244 children at increased genetic risk of type 1 diabetes before the age of 4 months. Participants will be randomised to either the control or intervention group based on the child's current breastfeeding status (currently breastfeeding or no longer breastfeeding). The intervention group will receive regular dietary and physical activity counselling. The primary outcome is β-cell health at 36 months, assessed by fasting and stimulated proinsulin-to-C-peptide ratio. Secondary outcomes include accelerated growth during infancy, overweight at 36 months, and time to development of persistent confirmed islet autoantibodies or type 1 diabetes. Growth measures, blood samples for serological markers, stool samples, dietary intake (nutrients and food group data) and questionnaire data will be collected regularly throughout the study period. Regression models will be used to estimate the effects of the intervention on the primary outcome. ETHICS AND DISSEMINATION: The research protocol was approved by the Swedish Ethical Review Authority (dnr 2024-05217-01, 2024-08622-02, 2025-01759-02). Study findings will be presented at national and international conferences, submitted for publication in peer-reviewed journals, shared on social media and disseminated through patient-education materials. TRIAL REGISTRATION NUMBER: NCT06670625.