Aims: The prevalence of gestational diabetes mellitus (GDM) is rising. There is little evidence to demonstrate the effectiveness of one dietary therapy over another. Our aim was to investigate the effect of a low glycaemic index (GI) versus a conventional high fiber (HF) diet on pregnancy outcomes, neonatal anthropometry and maternal metabolic profile in women at high risk of developing GDM.

Methods: A total of 139 women (mean±SD age: 34.7±0.4 y; mean±SD pre-pregnancy BMI: 25.3±0.5 kg/m²) at high risk of GDM (age≥35 yr, family history of type 2 diabetes mellitus, or BMI≥30 kg/m²) were randomised to follow a low GI (LGI, n=72; target GI≈50) or a high fiber, moderate GI diet (HF, n=67; target GI≈60). Women were enrolled into the study at 14-20 weeks gestation (mean 17.6±0.2 weeks). Dietary intake was assessed by 3 day food records. Anthropometry of the offspring was measured with a PeaPod®. Pregnancy outcomes were collected from the medical records. 

Results: The LGI group achieved a lower GI than the HF group (mean±SEM: 51±1 vs 58±1, p<0.001). At baseline 10 women had GDM in the LGI group and 11 in the HF group. Similar numbers of women developed GDM by week 28 (LGI group n=10 and HF group n=9). There were no differences in fasting glucose, HbA1c, fructosamine or lipids at 36 weeks gestation. There were no differences in birth weight (LGI 3270±50 vs HF 3260±60 g, p=0.906), ponderal index (LGI 2.71±0.03 vs HF 2.69±0.03 kg/m³, p=0.958), birth weight centile (LGI 46.2±3.2 vs HF 42.8±3.3, p=0.888), %fat (LGI 10±1 vs HF 10±1%, p=0.347), or adverse pregnancy outcomes. 

Conclusion: In intensively monitored women at high risk of GDM, a low GI diet and a conventional high fiber diet produce similar pregnancy outcomes.