Japan’s National Health and Nutrition Survey (NHNS) is the oldest of all national health examination surveys currently conducted in the world. The NHNS originally began as the National Nutrition Survey after World War II under the General Headquarters of the Allied Forces, to investigate the nutritional status of the civilian population undergoing food shortages and to secure emergency food aid from abroad. After the end of occupation in 1952, the survey continued under the Nutrition Improvement Law. As the nutritional status of the Japanese population improved, the focus of the survey shifted to the management of noncommunicable diseases. The National Nutrition Survey was redesigned and renamed the NHNS in 2003 under the Health Promotion Act, to cover various aspects of health for assessment of the risks for noncommunicable diseases. The history of the National Nutrition Survey from 1945 to 2000 has been described in detail elsewhere, ¹ and this paper focuses on the NHNS since 2003.

Objectives. We described changes in body mass index (BMI) and the prevalence of thinness among young Japanese women (aged 15–29 years) from 1976 to 2000 by reanalyzing the nationwide data in the National Nutrition Survey, Japan. Methods. We used height and weight data sets for 30 903 nonpregnant, nonlactating women during the 25-year period. We calculated the mean values of BMI and the prevalence of thinness for 3 age groups (15–19, 20–24, and 25–29 years of age). Results. Changes in BMI per 10 years were −0.17 kg/m², −0.22 kg/m², and −0.34 kg/m² for each age group, respectively. Extreme thinness (BMI < 17 kg/m²) increased from 2.4% in 1976–1980 to 4.2% in 1996–2000. Conclusions. Further studies regarding topics such as increased smoking prevalence are needed to identify the underlying causes of increasing thinness.