Although obesity is an increasing concern worldwide, over 20% of Japanese women in their twenties in the 2000s were underweight. However, many ultra-skinny models appear in the media, causing women to believe that being underweight is ideal. Many studies have reported that being underweight is harmful and causes several physical and mental symptoms. Different from other developed countries, a low birth weight is increasing despite medical progress in Japan because of mothers being underweight. This may negatively influence the health of newborns.
 Previous studies demonstrated that calorie restriction extends the healthy life span. However, a recent study that aimed at confirming the life-extending effects of calorie restriction in monkeys for thirty years revealed that calorie restriction at an old age extends the life span, whereas calorie restriction at a young age may reduce the life span.
 The normal BMI range of 18.5 to 25.0 set by WHO lacks substantial evidence. It should instead be defined based on the body weight with the lowest mortality. Recent studies found that the BMI associated with the lowest mortality increased in the last few decades because of medical advances for obesity-related diseases. Therefore, the risks of being underweight are now higher.
 In some European countries, ultra-skinny models are prohibited by the government from appearing in the media in order to correct the social trend that being underweight is ideal. However, there are no regulations for ultra-skinny models in Japan. The risks of dieting behaviors at a healthy body weight that lead to eating disorders are underestimated.
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