Dietary change after gestational diabetes mellitus for prevention of type two diabetes mellitus

Women with a history of gestational diabetes mellitus (GDM) are at an increased risk of developing type two diabetes mellitus (T2DM). Nutritional guidelines for the prevention of T2DM recommend a reduction of 7% of body weight if overweight, reduction in the intake of fat and an increase in the intake of dietary fibre. Current research indicates overweight and obesity and consumption of excessive dietary fat, are prevalent problems amongst women with prior GDM. Thus, there is a need to develop interventions targeted towards lifestyle change in these women. This thesis is a secondary analysis of dietary data from a pilot behavioural lifestyle intervention in women with prior GDM: the Healthy Living Program after Gestational Diabetes Mellitus (HeLP GDM) study. The following two central hypotheses were tested: 1. dietary change was achieved in the HeLP GDM study 2. the associated dietary intakes collected from two dietary assessment methods provided relatively comparable estimates of macronutrient intake. Methods: In the HeLP GDM study 59 overweight or obese women with prior GDM were randomised to either a six month telephone diet and physical activity behavioural change intervention group or a no treatment control group. For this thesis changes in intake of energy, fat and fibre from baseline to six months were analysed using nutrient estimates obtained from three day estimated food records and seven day telephone diet histories. Additionally change in body weight from baseline to six months was assessed using selfreported weight. To assess relative validity baseline diet history and food record paired data were compared for group differences. Change in bias from baseline to six months was assessed using paired t tests with individual precision and presence of systematic error determined by Bland Altman scatterplots. Results: At six months diet history analysis demonstrated the intervention group compared to the control group reduced energy by -1251 kJ (95%CI -2169, -332), total fat by -16.8 g (95% CI -28.5, -5.0) and saturated fat by -7.2 g (95% CI -12.2, -2.1). Analysis of food record data demonstrated only a relative reduction in saturated fat of -4.7 g (95% CI -9.0, -0.4) in the intervention group. The reduction in energy by -849 kJ (95% CI -1774, 76) and total fat by - 11.5 kJ (95% CI -23.2, 0.2) approached but failed to achieve statistical significance. Intervention participants were more likely than control participants to consume an intake of total fat less than ≤30 of total energy [9.2 greater odds (95% CI 2.1, 41.3)] and 15g per 4200kJ of fibre [8.5 greater odds (95% CI 2.0, 35.4)] identified by the diet history but not the food record. Greater reduction in energy intake by the intervention group was confirmed by a small but clinically significant reduction in weight of -2.4 kg (95% CI -4.5, -0.3). Relative validity analysis identified mean bias between paired food record and diet history estimates for all variables were not significantly different at baseline. For all variables no significant change was found in bias at six months. However for each nutrients there was a large standard deviation of the mean bias which indicated low precision between dietary assessment estimates. No linear relationships were demonstrated between bias and mean intake indicating an absence of systematic error for all variables. Conclusion: Dietary intervention targeted at overweight or obese women with prior GDM resulted in short term decreases in intake of energy, total fat and saturated fat, while an appropriate intake of dietary fibre was maintained. Furthermore the reduction in energy intake was accompanied by a decrease in body weight. Overall data obtained from both the diet history and food record compared well at the group level and both methods identified similar dietary change trends