When a woman goes into pregnancy already carrying excess weight, she’s at particular risk for metabolic and hormonal abnormalities that boost her odds for diabetes, preterm delivery and, ultimately, cardiovascular disease. And increasing evidence suggests that obesity creates a toxic in-utero environment that increases the baby’s birth weight and affects its development and future health.
So a big focus for obstetricians is to minimize weight gain during the pregnancy. Now, a small but intriguing randomized trial suggests that a low-glycemic-load diet is the best way to do that.
Low-GL diets are designed to moderately reduce total carb intake and substitute “good” carbs that are in low in sugar and release sugar slowly (read: whole grains, whole fruits and vegetables, nuts, legumes) for “bad” carbs (white bread and foods high in refined sugars). The study compared the low-GL diet with a standard low-fat diet.
The trial was small — just 46 women – and began relatively late (diets were started in the second or third trimester), so did not show a definitive difference in weight loss or in infant birthweight. Nonetheless, the low-GL group showed some unexpected benefits.
First, women following the low-GL diet were less likely to deliver before 38 weeks’ gestation. This was statistically and potentially clinically significant, because even “late preterm” babies (born at 37 to 38 weeks) have a 1.5- to 2-fold higher risk of adverse outcomes. Study leader David Ludwig, director of Children’s OWL Program, believes the difference may reflect a reduction in chronic inflammation in the low-GL group (as evidenced by a greater drop in the marker C-reactive protein). The low-GL group also had a greater drop in cholesterol, perhaps improving the health of blood vessels in the placenta, and a greater drop in triglycerides.
Infants in the low-GL group also had a larger head circumference, a gross measure of brain development that predicts early-childhood IQ. Ludwig isn’t sure why, but speculates that hormones affected by diet, such as insulin, could affect brain development. “It may be that hormonal changes redirect calories into fat tissue, leaving fewer calories available for brain growth,” he says.