Table 1 Participant inclusion/exclusion criteria

• Children (aged 11–17 years)

• BMI < 85% for age and sex

• T1D duration of 4–36 months

• Random C-peptide > 0.17 nml/L

• Able to consume test dose of prebiotic

• Monogenic forms of diabetes or type 2 diabetes

• History of ongoing infection or antibiotic treatment within the past 1–3 months

• History of immune-compromise, recurrent infections, steroid intake (inhaled or oral forms) or other immunosuppressant use in the past 6 months

• History of chronic gastrointestinal disease, including possible or confirmed celiac disease

• Pregnancy or possible pregnancy

• Allergy to corn (prebiotic) or milk, soy (present in the mixed meal) or their products

• Participation in other intervention research trials within prior 3 months

• Anticipated major change in diabetes management during the study (e.g., change from injections to insulin pump therapy or new to continuous glucose monitor usage)

• Consuming a high-fiber or vegetarian diet (consuming three or more servings of high-fiber foods on 4 or more days per week) or any fiber supplements