This group will receive a one-on-one counseling session during one visit with a Certified Diabetes Educator (CDE), who will provide standard advice on diabetes prevention and healthy lifestyle. They will receive a booklet on exercise and healthy diet as per current Canadian guidelines for healthy eating. This group will also receive a check-in telephone call from the Study Coordinator, half-way through the study. This group will not receive motivational interviewing, health coaching on low GI diet and/or exercise, or additional telephone follow-up.

Participants assigned to this arm will receive a combination of the home-based physical activity program with health coach and the home-based low-GI diet program with health coach, as described in the respective individual arms. The Health Coach for this group will be a CDE.

Participants will be counseled to follow physical activity recommendations for Canadians, which is at least 150 minutes of moderate physical activity per week. Participants will be asked to participate in aerobic, strength training and stretching activities. Health Coaches will use motivational interviewing, goal-setting and problem solving to assist participants in meeting their physical activity goals. More participants will be randomized to this group and the participants will either have CDE or a Registered Kinesiologist (R. Kin) as their health coach.

This arm will receive either a trained CDE or R. Kin as a health coach and a home-based physical activity program for 6 months. Health coaches will provide one-on-one motivational interviewing (MI) and goal-setting, and will account for baseline fitness, resources, childcare, and breastfeeding, to be undertaken at participants' homes or in their communities. Prescriptions will be based on minimum recommendations for moderate-intensity exercise for postpartum women. Participants will maintain at least 150 min/week of moderate activity at a target heart rate of 30-80% with a perceived exertion of 12-15 on the Borg Scale. They will also be counseled on resistance training and pelvic floor exercises. They will receive regular telephone-based coaching to advance goals. Phone-calls will be administered on a weekly basis during weeks 2-8 of the intervention, biweekly basis on weeks 10-12, and monthly basis on weeks 16-24.

Beta-cell function will be measured using the Insulin Secretion Sensitivity Index 2 (ISSI-2), which is an established oral glucose tolerance test (OGTT)-based measure of beta-cell function that has been validated against the disposition index from intravenous glucose tolerance test (ivGTT) and has been used in previous clinical trials. ISSI-2 is the product of insulin secretion [the ratio of area under-the-insulin-curve (AUCins) to area-under-the-glucose curve (AUCgluc)] and insulin sensitivity measured by the Matsuda index:

ISSI-2 = (AUCins / AUCgluc) × [10000 / √(Fglu × Fins × Mglu × Mins)]

Where Fglu = fasting glucose; Fins = fasting insulin; Mglu = mean glucose; Mins = mean insulin

These measures will be calculated using the glucose and insulin values at baseline, and at 60 and 120 minutes following a 75-gram oral glucose load.

For the effectiveness phase weight is now the primary outcome and change in baseline-adjusted pancreatic beta-cell function a secondary outcome. Weight in kilograms (kg) will be measured using a medical grade scale at the baseline and final health assessment.. We will also measure height in metres (m) using a medical grade stadiometer to calculate body-mass index (BMI, kg/m2). We will analyze the weight and height outcomes as continuous variables. We will then categorize BMI as under/normal weight (< 25 kg/m2), overweight (25.1-29.9 kg/m2), and obese (≥ 25 kg/m2). Finally, we will also calculate the proportion of participants who return to their pre-pregnancy weight or less, based on self-reported pre-pregnancy weight.

Feasibility measures will include recruitment, pre- and post-randomization attrition, adherence and follow-up rates, and symptoms, side effects, and satisfaction of the interventions. Adherence to exercise will be assessed with the International Physical Activity Questionnaire (IPAQ), physical activity records and accelerometer administered/worn at baseline, mid-study (week 12 of intervention) and follow-up, which estimates whether activity guidelines are met. Participant log books will be reviewed to assess diet and exercise adherence. Optimal adherence will be defined as meeting activity guidelines or consuming low GI foods at least 60% of the time for the exercise and diet arms respectively. Safety of interventions will also be assessed based on self-reported symptoms and side effects during telephone follow-up and at study end.

Participants will also complete questionnaires on satisfaction of the education and interventions throughout the study and at study end.

Exercise capacity: The primary endpoint for the exercise intervention will be baseline-adjusted exercise capacity at study end based on peak oxygen consumption (VO2max) from the graded exercise treadmill test. Change in metabolic equivalents (METs) and percent age-predicted fitness will also be calculated based on the Bruce protocol:

% age-predicted fitness = (100×observed MET)/age-predicted MET, where MET = VO2max / 3.5

Diet GI: The primary endpoint for the low GI diet intervention will be baseline-adjusted diet GI, which will be calculated using a three-day diet record using the following validated formula:

Dietary GI = [ΣC×F×GI]/[ΣC×F]

Where C=quantity of carbohydrate in age-specific portion of food; F=frequency of consumption/day; GI = GI of the food with glucose as the reference (GI=100).