Food glycemic index changes in overweight/obese pregnant women enrolled in a lifestyle program: a randomized controlled trial

BACKGROUND: The calculation of the glycemic index of food mirrors a rise in blood sugar levels. A low-glycemic index carbohydrate diet in pregnancy has been associated with normal infant birthweight. Thus, strategies to lower the food glycemic index could be successful in improving pregnancy outcomes. OBJECTIVE: The purpose of this study was to compare different prescribed diets on food glycemic index intake and its relationship with rate of large-for-gestational-age infants. STUDY DESIGN: At the 9th-12th week of gestation (with a gynecologist and a dietitian both present), 273 Italian women with a body mass index of ≥25 kg/m2 were assigned randomly either to a customized low-glycemic index diet that was detailed by a dietitian (customized intervention; n=139 women; 1800 kcal/d+30 minutes walking 4 times/wk) or to generic lifestyle advice (standard care; n=134 women) with counseling about a prudent diet and physical activity, according to Italian guidelines. At enrollment and at the 36th week of gestation, the food frequency questionnaire was completed. In 73 Italian foods, the glycemic index was assessed with the use of a classic formula (available carbohydrate×glycemic index prescribed/total carb content of the meal) then was subdivided according to meal pattern. The main outcome was the change in food- glycemic index. RESULTS: Sociodemographic features were similar between the groups. One hundred fifty-six women completed the study (customized intervention=81; standard care=75). The mean daily glycemic index decreased from 58.4±19 to 52.5±11.2 (P=.008) in the customized intervention group although it remained unchanged in the standard care group. After the intervention, women in the customized intervention group reported a significant decrease in the diet glycemic index at dinner compared with both lunch and breakfast values (P<.02). Lower birthweight and fewer large-for-gestational-age infants were observed in the customized intervention group. CONCLUSION: A customized low-glycemic index, calorie-restricted diet that was associated with constant physical activity effectively reduced the food glycemic index. This reduced food glycemic index is associated with lower rate of large-for-gestational-age newborn infants.