Female high school students who are underweight or who think of themselves as overweight may be at increased risk of engaging in unsafe sexual behavior.1 Among sexually active women participating in the 2005 Youth Risk Behavior Surveillance Survey, those with a low body mass index (BMI) had reduced odds of having used condoms the last time they had sex; those who considered themselves overweight had elevated odds of having initiated intercourse before age 13 and, regardless of the accuracy of their weight perception, reduced odds of reporting condom use at last sex. Associations between weight-related measures and risky behaviors varied among white, black and Latina young women.

Analysts used data on the 7,193 female participants in the nationally representative school-based survey to determine whether BMI, perceived weight and weight misperception were related to selected sexual behaviors. They categorized respondents as overweight if their BMI was at the 85th percentile or higher, as normal-weight if it was at least the fifth percentile but did not reach the 85th, and as low-BMI (or underweight) if it was below the fifth percentile. Using responses to a closed-ended question, they categorized participants as perceiving themselves to be “underweight,”“about right” or “overweight.” Comparisons of respondents’ BMI and perceived weight yielded the weight misperception measure. Separate analyses were conducted for whites (who made up 62% of the sample), blacks (15%) and Latinas (10%).

Overall, 69% of young women were normal-weight, 30% overweight and 2% underweight. Results of chi-square analyses indicated that whites were the most likely to be normal-weight (73%), and blacks the least likely (57%); no more than 2% of any group had a low BMI. Half of all teenagers considered their weight about right, four in 10 thought that they were overweight and the rest said that they were underweight; these findings were similar in all racial and ethnic groups. In the sample as a whole and in each subgroup, two-thirds of respondents assessed their weight accurately. Fifteen percent overall misperceived themselves as underweight, and 17% as overweight. Black teenagers were the most likely to wrongly classify themselves as underweight (23%) and the least likely to mistakenly think they were overweight (9%).

Half of women surveyed had had sex. Of those who had done so within the previous three months, 4% had first had intercourse before age 13, and 12% had had four or more partners in their lifetime; the last time they had had sex, 19% had been drinking, 56% had used condoms and 21% had been on the pill. Blacks were the most likely to report every risk behavior except alcohol use at last sex; whites were the most likely to report pill use, and blacks the most likely to report condom use at last sex.

In analyses that adjusted for age, race or ethnicity, and history of intimate partner violence (which was reported by 17% of respondents), BMI was associated with only one risky behavior: Underweight women were less likely than normal-weight women to report having used a condom at last sex (odds ratio, 0.4). Perceived weight, however, predicted a number of behaviors. Compared with women who considered their weight about right, those who thought of themselves as overweight were less likely ever to have had sex (0.8); among those who were sexually active, women who considered themselves overweight had elevated odds of having initiated sex before age 13 (1.6) and reduced odds of reporting condom use at last sex (0.8). Weight misperception was associated only with condom use at last sex: Women who incorrectly thought of themselves as being overweight were less likely than those who assessed themselves accurately to report this outcome (0.6).

Patterns of associations were very different for women of different races and ethnicities. Among whites, neither BMI nor perceived weight was related to risky behavior. However, those who underestimated their weight had elevated odds of being sexually experienced (odds ratio, 1.3) and, if they were sexually active, of having had four or more partners (1.9); among sexually active women, those who overestimated their weight had reduced odds of reporting condom use at last sex (0.5). For sexually active blacks, by contrast, a low BMI predicted a reduced likelihood of condom use at last sex (0.05), and the odds of having had four or more partners were raised if women thought of themselves as overweight (1.5). Among sexually active Latinas, all three weight-related measures were associated with risky behavior: Overweight women had increased odds of early sexual initiation (2.6), while underweight women were at risk of having had four or more partners (11.9). Sexually active Latinas who considered themselves overweight had elevated odds of having used alcohol at last sex (2.4), and those who underestimated their weight had elevated odds of early sex (3.3) and reduced odds of having had at least four partners (0.3).

The analysts point out that their study is limited by its cross-sectional design, its reliance on self-reported measures and the brief recall period used for the sexual behavior variables. However, they add that its use of a nationally representative sample and a variety of weight-related measures bolster the scant literature on the relationships between teenagers’ weight, self-image and sexual behavior. Their findings, they conclude, illustrate “that knowing how a girl perceives her weight may be as important [for reducing sexual risk] as knowing her actual weight” and that programs aimed at reducing teenagers’ risk may need to take into account their racial and ethnic background. —D. Hollander

REFERENCE

1. Akers AA et al., Exploring the relationship among weight, race, and sexual behaviors among girls, Pediatrics, 2009, 124:e913–e920, <http://www.pediatrics.org/cgi/content/full/124/5/e913>, accessed Oct. 28, 2009.