Race and parity in relationship to body weight

Nutrition Research Newsletter, Sept, 2005 by S. Lee, J. Sobal, E. Frongillo

Obesity in women is increasing in prevalence, with the proportion of obese women now at 33%, up from 25% a decade ago. Obesity is a growing risk factor for increased morbidity and mortality.

Child bearing is considered to be one of the important contributing factors to major weight gain and risk of becoming obese in women. Women's weight tends to increase the most during the first pregnancy compared with subsequent pregnancies. Subgroups of women also tend to be more vulnerable to weight gain with pregnancy and to the risk of becoming overweight. Black women show greater postpartum weight gain retention than white women. Racial differences in parity-related weight gain have not been fully examined. Rural residence has also been linked to greater risk of obesity in women, and living in nonmetropolitan areas may be related to greater postpartum weight retention. In addition to race and residence, a wide variety of biological, sociodemographic, and behavioral factors have been found to be associated with postpartum weight retention.

Researchers undertook a study to examine whether and how relationships between parity and body weight differ by race and size of place of residence, adjusting for various sociodemographic factors and health behaviors, in the Third National Health and Nutrition Examination Survey (NHANES III). NHANES III was conducted on a nationally representative probability sample of US residents from the contiguous 48 states from 1988 to 1994 by the National Center for Health Statistics. Among the total 33,199 people ha NHANES III, only white and black women of childbearing age were included in the analysis. After the exclusion process, a sample of 3398 women were included in the current analysis.

BMI was used as a measure of adiposity. Parity was classified as 1 through 4 based on the self-reported number of live births. Nulliparous women (those who had never given birth) were used as the reference group. Pace was categorized into white and black, as self-reported by respondent. Size of place of residence was available in the NHANES III data as a dichotomous variable of metropolitan and nonmetropolitan.

For these analyses, the sample was divided into four groups by race and size of place of residence: metropolitan white, nonmetropolitan white, metropolitan black, and nonmetropolitan black. Covariate measures included sociodemographic factors and health behaviors. Health behaviors included in the analyses were smoking, physical activity, diet (energy intake, fiber intake, percent energy from fat, and energy density of diet), use of birth control pills, and alcohol consumption.

The parity-weight relationships varied by race and size of place of residence. After adjusting for the covariates, significant relationships between parity and body weight were found only in black women in metropolitan areas and white women in nonmetropolitan areas. Compared with women with no children, white women with two children living in nonmetropolitan areas tended to have lower BMIs, whereas black women in metropolitan areas with one or two children showed higher BMIs.

The parity-weight relationships in these groups of women were not strong or linear. However, the parity-weight relationships of black women in nonmetropolitan areas warrant further examination.

S. Lee, J. Sobal, E. Frongillo, et al. Parity and body weight in the United States: Differences by race and size of place of residence. Obes Res; 13:1263-1269 (July, 2005) [Correspondence: Soo-Kyung Lee, Department of Nutritional Sciences, Rutgers, State University of New Jersey, 26 Nichol Avenue, New Brunswick, NJ 08901-2882. E-mail: SKLee@aesop.rutgers.edu]