When our mothers were pregnant, they were encouraged to take a second helping. “Have another. You’re eating for two!” was a common refrain. The pregnancy weight gain landscape has changed significantly since those days. In developed countries, one third of women are overweight or obese during their childbearing years. New research is pushing the boundaries of what constitutes healthy calorie intake and weight gain during pregnancy. A new systemic review in the April 2016 Gray Journal examines eighteen studies on weight gain and calorie intake during pregnancy to answer the question: how much extra food should women eat during pregnancy to optimize weight gain?
Weight gain in pregnancy is know to increase the risk of many pregnancy complications, such as gestational diabetes, high blood pressure, preeclampsia, and even the need for cesarean section. Mothers who are obese give birth to infants who are at increased risk of stillbirth, preterm birth, congenital malformations, and high birth weight. Children of overweight and obese women are at increased risk of obesity themselves, leading to a cycle of high health risks. Optimal weight gain during pregnancy is a critical step in breaking the cycle.
Many of our current recommendations come from theoretical calculations. Mathematicians calculated out the number of extra calories a woman would need to eat in a day to achieve the recommended weight gain for each trimester. These numbers come out to a lot less than “eating for two.” It’s very difficult for normal people to add just an exact extra number of calories, and who is to say if adding this number of calories actually results in the “perfect” pregnancy weight gain? It depends on a woman’s pre-pregnancy weight, age, exercise level, metabolism, amongst other factors. Many women gain more than the optimal amount of weight during pregnancy, and losing that weight is difficult after pregnancy when there is a newborn to care for!
The newest research suggests that eating the recommended increased intake will actually lead to too much weight gain. One analysis of 23 studies showed that the average, well-nourished woman only ate an extra 33 calories a day to achieve a healthy pregnancy weight. Perhaps, as we are sitting more and exercising less, we don’t need to eat as much to gain the optimal amount of weight.
This new analysis examined data from 18 studies and a total of 2,644 women from countries around the world. Most of the studies were observational, but four were randomized clinical trials, the gold standard of medical research. Most studies used food records to estimate women’s caloric intake. Women reported eating an average of about 2,000 calories a day during pregnancy. They ate an average of 110 extra calories during pregnancy, which was not statistically significantly different from the amount they ate before pregnancy. They did, however, gain weight during pregnancy- an average of 26 pounds, which is about the recommended weight gain for normal weight women. Perhaps most interestingly, the amount of weight gained did not correlate with the amount of calories taken in. The analysis also showed that there was no difference in mean calorie intake between women in low, normal, and overweight groupings. Most women gained 22 to 35 pounds, as recommended for normal weight women. Underweight women tended to gain less than recommended, and overweight and obese women tended to gain more than recommended.
Unfortunately, the methods for assessing dietary intake were not perfect- estimates, really. But, the weight gain numbers were solid and point to an interesting trend. Perhaps women do not need to significantly alter their diets during pregnancy. Or, perhaps calories just aren’t important, and food content, glycemic index, types of fats and other food qualities matter more. Nevertheless, this analysis of 18 studies and the first analysis of 23 studies both point to healthy weight gain linked to a small (if any) increase in caloric intake, calling into question our current recommendations.