The Breakfast Rise, Education and Knowledge Study (BREAK)

This is a quantitative study. Dexcom CGM data will be collected for the period of recording. Participants will be asked to test three breakfast meals on two occasions and submit a postprandial questionnaire after each test meal to confirm it has been tested. The postprandial period will be three hours following the end of the breakfast test meal. The test meal recipes will be provided by the chief investigator. The dietary composition of the meals has been analysed using the a dietary analysis programme. The glycaemic index and load of the meals is estimated from this programme which uses available date from the international tables of glycaemic index and glycaemic loads (Atkinson et al. 2008; 2021). Most foods were based on average composition across different brands. For the added fibre bread used in test meal 3, an average of three known brands was used calculated by the chief investigator. The meals will be taken in the home environment with the food provided by the families. The participants will be asked to take the test meal on a day when their CGM reading is between 4-10mmol/l and when there has been no nocturnal hypoglycaemia on the night before the planned test. The participants will act as their own control. They will be asked to complete a postprandial questionnaire for control meals as well. The control meals will be there usual breakfast of choice. The study duration, commencing with the recruitment of the first participant and ending when data has been fully described, is anticipated to be two years.

Recruitment Paediatric diabetes dietitians, working across the UK, will be enrolled to help recruit participants and become principal investigators (PI) for their site.

Sample size The sample size power calculation is 64. This is based on using ANOVA repeated measures, within factors with four groups and measurements (3 test meals and control) with small effect size (0.15), P value 0.05 and power 0.80 and correlation among repeated measure of 0.5. The drop rate of clinical trials is often over 40%. Therefore, the aim is to recruit 90 participants to allow for this dropout rate and meet the sample size of 64. It may be possible to recruit this number of participants. There are approximately 29,000 children and young people living in the UK with T1D (Juvenile Diabetes Research Federation (JDRF), 2018). In the first phase of this study, 12 NHS sites were enrolled, and 96 children and young people were recruited to the study.

Methodology Baseline data

In order to make comparisons between relevant variables and glucose levels, the following baseline data will be collected from the dietitians and sent to the chief investigator, along with the artificial identifier on the Excel spreadsheet as discussed earlier at the stage of recruitment of participants:

• Parent's email address
• Sex, date of birth and recent weight and height (for calculation of BMI and BMI centile) and date of when this was taken
• Date of diagnosis of T1D
• Last four HbA1c
• Total daily insulin dose (TDD)
• Insulin: carbohydrate ratios (ICR) and Insulin Sensitivity Factor (ISF)
• Current insulin regimen - including the type of insulin prescribed and if applicable type of insulin pump i.e. open or closed loop system.

Run-in period At recruitment the dietitians will be asked to arrange a review of the participants insulin regimen including the insulin to carbohydrate ratio's (ICR), insulin sensitivity factor (ISF) and basal background insulin doses/rates. The dietitian will be asked to inform the chief investigator when this has taken place. Participants will be asked to commence the test meals following this.

Glucose measurement Data on interstitial glucose will be collected via Dexcom CGM. The Dexcom CGM data will be accessed by an NHS Highland research 'Clarity Clinic' with Dexcom CLARITY® Clinic Portal (Dexcom In, San Diego, California (CA), USA). The chief investigator is administrator of this clinic. Once the managing dietitian has obtained each participant's consent, the participant's parent's email address will be sent to the chief investigator along with the baseline information/data as described above. The chief investigator, as administrator of the Clarity Clinic account, will then invite the participant, via email, to be added to the clinic. Once the invite has been accepted, it will stand for the period of the recording i.e. until all the test meals and questionnaires have been completed. Once the participant has submitted their last questionnaire, they will be removed from the Dexcom CLARITY® Clinic Portal.

Following the provision of CGM data and review of the insulin regimen by the diabetes team, participants will be randomised to test each of the three test meals on two separate occasions with a control meal (usual breakfast meal) for each test meal. Randomisation will be achieved using a Latin square randomisation. The tool used for this will be http://www.jerrydallal.com/random/randomize.htm. Randomisation will be done in a block of four.

The test meals are based on foods children and young people enjoy eating. There are three meals. Test meal one includes a high glycaemic index cereal meal with milk and has a high glycaemic load (> 20), test meal two is the same cereal meal with a high glycaemic load (>20) with addition of 10g protein and test meal three has a medium glycaemic load (10-20). For test meals one and two there are three portion size options to meet age appropriate requirements and appetites. The participants will be able to choose from two different cereals for test meal 1 and a choice of protein sources for test meal 2. They will be asked to keep to the same choice of cereal and protein source for the repeat meal. They will be asked to consume at least 75% of the meal to ensure the threshold of the glycaemic load is met. The instructions and details of the test meals are presented in Appendix 11. The control meals will be the participant's usual breakfast of choice.

Participants will be asked to follow their usual insulin regimen as advised by their diabetes team i.e. their usual insulin dose and dose timing. For both test and control meals participants will be asked to avoid any further food intake during three-hour postprandial period other than carbohydrate adjustments required to treat any hypoglycaemia. Participants will also be asked to avoid drinks except water or carbohydrate free juices. They will also be asked to avoid physical activity of more than 30 minutes in duration. To minimise disruption to their normal daily activities, they will be advised to test the meal on a day when there is no planned physical activity i.e. a school day with no morning physical education. The CGM data will be collected throughout this time as discussed above.

Postprandial Questionnaire The participants will be asked to complete a postprandial questionnaire using 'online survey'. This includes questions about the meal and the three-hour postprandial period. The questionnaire is presented in Appendix 10. They will be asked to wait a minimum of three hours before answering and submitting the questionnaire. They will be encouraged to complete it on the same day as the test or control meal.

Data analysis This will be a mix of univariate, bivariate and multivariate analysis as this is best suited to describing, summarising and visualising these data. Outputs will include the distribution of glucose levels post-breakfast to determine the spread and dispersion of the data.