We investigated whether food supplementation within the first year life or age at introduction of gluten-containing foods influenced the risk of developing islet autoimmunity and type 1 diabetes. A total of 2,291 children with a family history of type 1 diabetes were prospectively followed from birth for 28,983 patient years (median 13.1 years). Dietary exposure data were collected by questionnaires, food records and by family interview. Exposure to gluten-containing foods before age 3 months, which occurred in 19 children, increased the risk of developing islet autoantibodies (n = 4), multiple islet autoantibodies (n = 4), and type 1 diabetes (n = 3) compared to exclusive breastfeeding within the first 3 months [adjusted hazard ratio (HR) 3.97 (95 % confidence interval 1.41-11.17), 5.39 (1.89-15.35), and 3.45 (1.04-11.48), respectively] and also compared to first exposure to gluten between 3.1 and 6.0 months of age [adjusted HR 3.40 (1.19-9.70), 4.25 (1.47-12.26), and 3.43 (1.01-11.66), respectively]. Children who received infant formula or other solid food within the first 3 months and children who received gluten-containing foods after age 6 months did not have an increased risk of islet autoantibodies, multiple islet autoantibodies or type 1 diabetes. Our present data affirm that compliance to infant feeding guidelines is a possible way to reduce type 1 diabetes risk in genetically susceptible children.