Heterogeneity Informed Nutrition Therapy for Gestational Diabetes Mellitus (HINT-GDM)

The hypothesis for this study is that women with different physiologic subtypes of gestational diabetes (GDM) (insulin secretion deficit vs. insulin sensitivity deficit) will differ in their glycemic responses to meals with different portions of dietary macronutrients. Investigators will determine GDM subtype based on glucose and insulin levels taken at multiple time points during an oral glucose tolerance test. Participants will consume two meals with different macronutrient content while wearing a continuous glucose monitor which will allow investigators to assess the glycemic response to the meals.

Diabetes mellitus can be classified based on impairments in two different physiologic parameters, insulin secretion and insulin sensitivity. The investigator involved in this trial has previously defined GDM subtypes based on underlying physiology and demonstrated that women with GDM and predominant sensitivity defects have an elevated risk of adverse pregnancy outcomes, while women with predominant secretion defects do not appear to carry the same risk. This supports the idea that not all gestational diabetes is the same. Ideal treatment strategies may differ between GDM subtypes. In this trial, investigators will evaluate the postprandial glycemic response to two test meals with different macronutrient content in different GDM physiologic subtypes. Two test meals with different macronutrient proportions have been designed by research dieticians. Participants will eat test meals at home for breakfast in a randomized order after an overnight fast. Participants will complete food and blood sugar diaries, and will wear a continuous glucose monitor, which will measure postprandial glucose.

Participants defined as having abnormal insulin sensitivity without an absolute defect in insulin secretion.

Participants who cannot be classified as having abnormal insulin secretion or abnormal insulin sensitivity or who have both abnormal insulin sensitivity and abnormal insulin secretion.

Area under the curve of CGM measured glucose from the start of the test meal to three hours after the test meal is started

Length of time at which the patient's BG are within goal range (65-140 mg/dl) on the day of test meal assessed by CGM

Inclusion Criteria: -Diagnosis of gestational diabetes Exclusion Criteria: Known diabetes mellitus that preceded pregnancy Food allergies to components of the test meals Use of medications known to affect glucose tolerance Have extensive skin changes or diseases making CGM sensor use problematic Demonstrated allergy to CGM adhesive Inability to adhere to the swimming and bathing instructions Plan to have MRI, CT scan, X Ray or diathermy (heat treatment) during the 7-day CGM study period Inability to adhere to Vitamin C guidelines during study period (using more than 500 mg of Vitamin C/day which could interfere with the CGM) Use of medications known to affect glucose tolerance In the opinion of the principal investigator (PI), demonstrate any other factor likely to limit compliance with the protocol

Powe CE, Allard C, Battista MC, Doyon M, Bouchard L, Ecker JL, Perron P, Florez JC, Thadhani R, Hivert MF. Heterogeneous Contribution of Insulin Sensitivity and Secretion Defects to Gestational Diabetes Mellitus. Diabetes Care. 2016 Jun;39(6):1052-5. doi: 10.2337/dc15-2672. Epub 2016 May 13.