This article contains descriptions of eating disorders that may affect some readers.
As a teenager, Sarah Mizugochi, who is 1.64 meters tall, was underweight.
“I thought about food all the time and was always hungry. I only ate cake once a year, on my birthday, and that lasted for three to four years. I wasn’t happy at all.”
Cases like Sarah’s, who is now 29, are so common in Japan that the prevalence of underweight among young women has become a serious health problem.
A survey conducted by Japan’s Ministry of Health in 2019 found that 20.7% of women aged 20 to 29 were clinically underweight, defined as having a body mass index (BMI) below 18.5. Sarah’s BMI was below the healthy weight range.
The World Health Organization (WHO) recommends that people aim for a BMI between 18.5 and 25.
Japan is the only high-income country in the world with such a high prevalence of underweight women. Similar rates are only found in poorer countries like Timor-Leste, Burundi, Eritrea, and Niger, according to a 2024 global study on trends in underweight and obesity published in the medical journal The Lancet.
In 1990, Japanese women had fewer underweight problems than today, and Japan was not an outlier in international statistics. Now it is.
Several studies and national surveys have revealed a growing trend toward thinness among young women.
A few years ago, the term “Cinderella weight” circulated among young women in Japan. The term refers to a BMI just below the healthy weight range, which is officially classified as underweight in the BMI scale, but which many women want to achieve.
However, Cinderella weight (in kilograms), which is calculated by squaring a person’s height in meters and then multiplying that number by 18, sparked a debate online. Some people spoke out against what they saw as an unrealistic and unhealthy goal.
Cultural Norm
Tomohiro Yasuda, a professor at Seirei Christopher University’s School of Nursing in Hamamatsu, Shizuoka Prefecture, studied underweight young women in Japan.
His research showed that while the women admitted they needed to gain weight, their idea of how much weight they needed to gain was far less than what would be required for a healthy BMI.
The underweight women in his study needed to gain an average of 10.3 kg to reach the ideal weight (defined as a BMI of 22), but when asked, they said they wanted to gain an average of only 0.4 kg.
“In Japan, there is a prevalence among young women of being underweight, which increases the risk of infertility, low birth weight, and sarcopenia (a type of muscle loss that typically occurs with aging and/or immobility),” the expert told the BBC.
Malnutrition can lead to bone loss, anemia, and menstrual irregularities, while insufficient protein intake tends to cause low muscle mass.
Some students in Professor Yasuda’s class on obesity and thinness said they wanted to lose weight because their favorite celebrities and influencers were thin.
“It has a lot to do with the strong influence of Japanese media and the long-standing admiration for the U.S. and Europe, which have led fashion and other aspects of Japanese culture for some time,” he says.
Professor Yasuda explains that, in Japanese media, men appear as people of various ages and appearances, while women are often portrayed as young and thin.
“And because so many young women are portrayed as thin, it creates the impression that ‘thin people are better,'” he adds.