MONDAY, Feb. 28 (HealthDay News) -- The stress of parenthood can lead new moms to forego physical activity and gain weight, researchers report.

The Georgia Health Sciences University team checked the body-mass index (BMI) of 60 first-time mothers who were asked about their levels of stress and physical activity.

"Sedentary lifestyle, or a low amount of physical activity, was most influenced by the type of parenting stress [that] the mothers reported. More parenting stress, including depression, was associated with less physical activity and a higher postpartum BMI," Dr. Deborah Young-Hyman, a behavioral psychologist with the Georgia Prevention Institute, said in a GHSU news release.

She and her colleagues also found that social interaction was associated with a higher BMI.

"We think women are socializing with their friends, not isolating themselves, but they are doing sedentary things like talking on the phone, watching television or hanging out at home, instead of taking their babies on a walk together," Young-Hyman said.

And the higher BMIs packed a psychological wallop.

New moms with a higher BMI had more depressive symptoms, while those with lower BMIs were more physically active and had fewer depressive symptoms.

"We know that physical activity improves your mood and helps you lose weight, but no one has ever asked how physical activity is related to parenting stress in first-time moms," Young-Hyman said.

She noted that being in a good mood is associated with higher levels of physical activity and lower intake of calories.

The study was published recently in Women and Health.

More information

The American College of Obstetricians and Gynecologists outlines how to get in shape after having a baby.