Pre-Pregnancy Dieters Gain Too Much Weight

Oct. 1, 2008 -- Women who diet before pregnancy tend to gain too much weight during pregnancy.

Even women who succeed in controlling their weight before pregnancy tend to gain too much weight while they're carrying a child, say Anna Maria Siega-Riz, PhD, RD, and colleagues at the University of North Carolina at Chapel Hill.

"When they are not pregnant, many women are really trying to hold their weight down. But when they become pregnant the message they get is 'Eat for two; give in to your cravings,'" Siega-Riz tells WebMD.

The UNC researchers asked 1,223 women who had just become pregnant about their previous dietary habits. About half the women had restrained their eating habits in some way. They simply cut back on what they ate, followed specific diet plans, and/or cycled between gaining and losing weight.

Regardless of how they did it, all normal-weight, overweight, or obese women who had tried to restrict their diets gained more weight during pregnancy than did women who did not diet before pregnancy.

Moreover, the pre-pregnancy dieters gained more weight during pregnancy than doctors recommend -- putting themselves and their babies at risk.

Women who gain too much weight during pregnancy have more C-sections, more preeclampsia, and are more likely to have babies with growth problems, says obstetrician J. Christopher Glantz, MD, MPH, director of the perinatal outreach program at the University of Rochester Medical Center.

"You might think people who are dieting before pregnancy would tend to gain less weight. Not only is that not true, this study shows that in pretty much all weight categories, the restrained eaters seem to gain more weight once they get pregnant," Glantz tells WebMD.

Surprisingly, normal-weight women don't need much more food once they're pregnant:

• Extra daily calories needed during the first trimester: 0
• Extra daily calories needed during the second trimester: 340
• Extra daily calories needed during the third trimester: 450

It's a different story only for women who are underweight before pregnancy, but who restrict their diets anyway. These women, Siega-Riz and colleagues found, did not gain enough weight during pregnancy -- and many likely suffer from eating disorders.

"Pregnancy doesn't require you to eat that much more calories -- just an extra glass of milk and an apple during the last two trimesters," Siega-Riz says. "But you have to make sure you are eating a nutrient-dense, healthy diet and not becoming physically inactive."

Glantz says the findings suggest that women, especially those whose weight goes up and down, may not have a good internal sense of how much food they really need.

"In these cases, it would be important to have a nutritionist meet with these patients, because most obstetricians -- including me -- don't have the training to know what specifically to recommend," he says.

"The amount of weight you gain during pregnancy is important for the health of your child and for your own future health," Siega-Riz says. "A lot of women think, 'I will just gain anything and just get it off later. That doesn't happen, because it is really hard to lose weight in the postpartum period."

The study appears in the October issue of the Journal of the American Dietetic Association.