Obesity Case 5

A 28 year-old woman seeks advice about prevention of gestational diabetes mellitus. Three of her sisters have had pregnancies complicated by gestational diabetes mellitus (GDM). Although good randomized trial data evaluating whether specific diets can prevent gestational diabetes are lacking, she was advised to lose weight. Eighteen months later, the patient has not succeeded in losing any weight, but has become pregnant. She continues to follow a typical Western diet with an abundance of processed food. She walks for 20 minutes five days per week. She comes to your office at 26 weeks of gestation because her glucose tolerance test showed gestational diabetes.

Question 1

Which of the following statements reflect the best available evidence regarding which diet she should follow to control her blood sugars?

A. A Mediterranean diet followed during pregnancy will help control gestational diabetes.
B. A low fat diet will help control gestational diabetes
C. A low glycemic index (GI) diet will help control gestational diabetes.
D. Energy restriction is not recommended during pregnancy.
Correct Answer
C. A low glycemic index (GI) diet will help control gestational diabetes.

A low GI diet is typically advised as treatment for women with GDM. Although data from randomized control trials is limited, low GI diets have demonstrated benefits and no harm. In a meta-analysis, low GI diets demonstrated a lower risk of macrosomia and a lower risk of insulin usage. Additionally, low GI diets with increased dietary fiber have been shown to reduce the risk of macrosomia beyond that of a low glycemic index diet alone.

Most clinical practice guidelines recommend that women with gestational diabetes limit carbohydrate intake to 35% to 45% of total calories with a minimum of 175 g/day to avoid ketogenesis, distributed in three small- to moderate-sized meals and two to four snacks, including an evening snack. The carbohydrate choices should preferably be low glycemic index with increased dietary fiber.Energy restriction is recommended by the Endocrine Society with their guideline that women with obesity and overt or gestational diabetes reduce their calorie intake by approximately one-third (compared with their usual intake before pregnancy) while maintaining a minimum intake of 1600 to 1800 kcal/d.

For her next pregnancy, assuming that she is not diagnosed with diabetes at the conclusion of the current pregnancy, it is unclear which dietary recommendations should be given to prevent repeat gestational diabetes. Large population surveys have demonstrated that women eating the highest quantities of plant-based carbohydrate and protein and the lowest amount of saturated fat/red meat are least likely to be subsequently diagnosed with gestational diabetes mellitus (independent of body mass index). Low glycemic index and low carbohydrate diets have not been shown to be effective in preventing GDM in prospective randomized control trials. Low fat diets have been shown to reduce the risk of type 2 diabetes mellitus in persons with impaired glucose tolerance, but have not been studied in a population likely to develop GDM.