High vs Low Glycemic Index Mixed Meal Tolerance Test in Children and Adolescents with Cystic Fibrosis

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PROJECT SUMMARY Cystic fibrosis related diabetes (CFRD) is one of the most common co-morbidities seen in patients with cystic fibrosis. Unlike CF patients without diabetes, CFRD patients have a higher mortality rates and a decline in pulmonary function due to abnormalities in glucose tolerance that often predate the diagnosis of CFRD. Sustained exposure of the islet cell to modestly elevated blood glucose levels is often cited as an important cause of beta cell dysfunction. Recent published data from our adult CF center and others show that patients with CF often consume a low-quality diet with high added sugar intake. We are particularly concerned that a diet which is abundant in high glycemic index (GI) foods and sugar sweetened beverages (SSB) may increase beta cell dysfunction in CF. We propose that we can successfully conduct a feasibility study, which will involve the consenting and randomizing of participants, the following of protocols and gathering of study data, and an evaluation of procedural acceptability from participants. Secondarily, we anticipate that an analysis of outcome data collected from this feasibility study will allow for preliminary data of the association between postprandial changes in glucose and redox imbalance following a mixed meal tolerance test. To test this, we propose the following Aims: Aim 1) Determine the feasibility and acceptability of conducting a randomized, balanced 2x2 factorial design that evaluates postprandial changes in glucose following exposure to a mixed meal that varies by GI and consumption of a SSB. A few of the metrics to evaluate feasibility will include a willingness from participants to consent and be randomized (<20% refusal), high protocol fidelity among investigators and participants (≥85%), high visit attendance by participants (≥85%) and high retention (≥80%), and completion of the primary clinical outcome measurements (≥90%), among others. Aim 2) Evaluate preliminary changes in postprandial hyperglycemia, islet cell function and incretin response to a high or low GI mixed meal tolerance test (MMTT) with and without SSBs in adolescents with CF. Subjects will be equally randomized to either sugar sweetened beverage plus high glycemic index (SSB+HI-GI), sugar sweetened beverage plus low glycemic index (SSB+LO-GI), no sugar sweetened beverage plus high glycemic index (NSSB+HI-GI), or no sugar sweetened beverage plus low glycemic index (NSSB+LO-GI) using permuted blocks. Sub Aim 2) Determine if an association exists between high vs. low GI MMTT with and without SSB and changes in plasma aminothiol redox imbalance.