This is a secondary analysis of 621 women in ROLO study, a randomized control trial of low glycemic index (GI) diet in pregnancy to prevent the recurrence of macrosomia, which aims to assess the effect of the diet on maternal and fetal insulin resistance, leptin, and markers of inflammation. In early pregnancy and at 28 weeks, serum was analyzed for insulin, leptin, tumor necrosis factor α (TNF-α), and interleukin 6 (IL-6). At delivery, cord blood concentrations of leptin, TNF-α, IL-6, and C-peptide were recorded. We found no difference between those who did or did not receive low GI advice with respect to the concentrations of any marker in early pregnancy, at 28 weeks or in cord blood. Women in the intervention arm of the study did have a lower overall rise in insulin concentrations from early pregnancy to 28 weeks gestation, P = .04. Of the women in the intervention arm, 20% were in the highest quartile for insulin change (28-week insulin − insulin at booking) compared to 29% of controls (P = .02). In conclusion, a low GI diet in pregnancy has little effect on leptin and markers of inflammation although an attenuated response to the typical increase in insulin resistance seen in pregnancy with advancing gestation was seen in those who received the low GI advice.