Knowledge of the risks associated with being underweight and body shape differences among young Japanese women: a cross-sectional study.

Abstract

Background: In Japan, approximately 20% of young women are underweight, a rate higher than that of other developed countries. For women, being underweight at a young age has been associated with amenorrhea, eating disorders, osteoporosis, and adverse pregnancy outcomes. We investigated young women's knowledge of these risks and associated factors.

Methods: A web-based survey was conducted among 984 Japanese women aged 18-29 years. The survey included questions about actual body weight, perceived healthy weight, body image, eating disorder tendency, knowledge of various risks and factors associated with being underweight, and sources of this knowledge. Participants were divided into underweight (< 18.5 kg/m²), normal weight (18.5-25 kg/m²), and obese (≥ 25 kg/m²) groups based on their body mass index (BMI). The body image and knowledge of health risks associated with being underweight were compared across the three groups and with women with and without an eating disorder tendency.

Results: Among the participants, 31.5% were underweight (BMI < 18.5 kg/m²). Of these, 87.4% considered their subjective ideal weight to be underweight, and 66.1% viewed their subjective healthy weight similarly. Underweight women reported greater body satisfaction than did those in other body shape groups. While 73.2% recognized amenorrhea as a risk of being underweight, only approximately half identified infertility, eating disorders, and osteoporosis as risks and associated factors, and few were aware of adverse pregnancy outcomes. Knowledge levels did not differ between underweight and normal-weight women. Conversely, women with a tendency toward an eating disorder were more aware of the risks of osteoporosis (58.6% vs. 49.0%) and eating disorders (66.8% vs. 55.2%) than were women without a tendency toward an eating disorder.

Conclusions: Young Japanese women had insufficient knowledge about the adverse pregnancy outcomes associated with being underweight. Underweight women are not less aware of the health risks and associated factors associated with underweight than normal-weight women. The body shape of young women may not be influenced by their knowledge of health issues associated with being underweight.