MAIN STUDY: Low Glycaemic Index (GI) Diet in the Management of GDM SUB-STUDY: The Breast Milk Sub-Study

The Effect of a Low GI Diet on Maternal and Neonatal Markers of Glycaemic Control and Postpartum Diabetes Risk SUBSTUDY The Effect of a Low GI Diet on Postpartum Markers of Oxidation in Breast Milk of Women With Gestational Hyperglycaemia

MAIN STUDY: Low glycaemic index (GI) diets are recommended by the Canadian Diabetes Association for treating type 1 and 2 diabetes mellitus (DM), but the role of GI in the management of gestational diabetes(GDM)is not yet clear. The main purpose of this study is to determine the effect of a low GI diet on blood sugar control in women with GDM. The effect of a low GI diet on maternal oxidative stress, pregnancy and delivery outcomes and markers of risk for diabetes after birth in both the mother and baby will also be assessed. SUB-STUDY: The main purpose of the sub-study is to determine if the breast milk (BM) of women with GDM consuming a low GI diet will have a higher antioxidant capacity than the BM of women receiving a medium-high GI diet (control/standard care). The effect of a low glycaemic index diet on maternal dietary intake of specific nutrient-antioxidants (i.e. vitamin C, E, and beta-carotene) (prenatal and postpartum) and concentration of vitamin C, E, and beta-carotene in participants' transitional and mature BM will also be assessed. The ORAC (Oxygen radical absorbance capacity) assay will be used to assess overall antioxidant capacity. The antioxidant capacity of BM in women with GDM will also be compared with that of women without GDM.

Hypotheses:

MAIN: The use of low-GI foods in the management of GDM reduces postprandial BG and oxidative stress; thereby reducing maternal and infant perinatal complications.

SUB-STUDY: Breast milk (BM) of women with GDM consuming a low GI diet will have higher BM antioxidant than women receiving the medium to high GI diet. BM of women with GDM will have lower antioxidant capacity than that of women without GDM.

MAIN STUDY: Use of low GI education is currently accepted by the Canadian Diabetes Association in treatment of type 1 and 2 DM, but is not included in the clinical practice guidelines(CPG) for management of GDM. Data collected to date support use of low GI in treatment of GDM, but more data are needed to influence CPG. In this study the effect of a low GI diet on maternal and neonatal markers of glycaemic control and postpartum diabetes risk in mother and baby will be determined. This study will also assess the role that maternal oxidative stress may play in this relationship.

Hypothesis: The use of low-GI foods in the management of GDM reduces postprandial BG and oxidative stress; thereby reducing maternal and infant perinatal complications.

SUB-STUDY: Breast milk (BM) is accepted as the optimal source of nutrition for infants. A wealth of literature on BM composition exists. This work includes measurement of antioxidants in BM. Women diagnosed with gestational hyperglycaemia have decreased antioxidant capacity in comparison to normoglycaemic pregnant women. A direct relationship exists between postprandial glycaemic response and oxidative stress. Low GI carbohydrate is converted to blood glucose (BG) more slowly than medium to high GI carbohydrate

Hypotheses: Breast milk (BM) of women with GDM consuming a low GI diet will have higher BM antioxidant than women receiving the medium to high GI diet. BM of women with GDM will have lower anti-oxidant capacity than that of women without GDM.

MAIN STUDY

Inclusion Criteria:

Women:

1. ≥ 18 years of age
2. diagnosed with gestational diabetes mellitus (GDM) or impaired glucose tolerance of pregnancy (IGTP) according to Canadian Diabetes Association (CDA) criteria
3. being followed within DIP (one of 4 sites)
4. willing and able to give informed consent
5. willing and able to comply with the study protocol

Exclusion Criteria:

Women:

1. with acute or chronic illness other than GDM or IGTP or use of drug (other than insulin) which may affect carbohydrate metabolism, gastrointestinal function or carbohydrate digestion (i.e. crohn's disease, HIV/AIDS, liver disease, kidney disease etc.).
2. known to have type 1 or type 2 DM prior to pregnancy
3. known multi-fetal pregnancy at enrolment
4. ≥ 33 weeks' gestation
5. prescribed oral anti-hyperglycaemic medication
6. insurmountable language barriers

SUB-STUDY control group (women without GDM) Same as for Main study except absence of GDM