Eating disorder charity Beat believes this issue is being fuelled by the increasing use of social media, as more young women are suffering from functional hypothalamic amenorrhoea. This is a condition where the body enters survival mode because it is severely under-fuelled. It results in menstruation stopping, but it can be reversed.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/why-are-more-young-women-losing-their-periods-due-to-restrictive-diets-and-excessive-exercise