Understanding and Addressing Girlfriend's Underweight Concerns

Question
Hello Doctor,

This is regarding my girlfriend. We know each other from past 16years and I really love her a lot, we are planning to get married in 2-3 years. She is 22 yrs old 5ft 2" tall. The other day we checked her weight and since then I'm soo worried. She weighs only 38 kilos which I know is too less for a girl of her age/height. She said she was 41 kilos 6 months ago and i know she reduced to 38 because she wasn't eating well. She says she used to weigh 38 at the age of 15.  

She is quite healthy and active and its been like 10yrs or more since she has seen a doctor or fallen sick. The only issue with her health i know is that she feels like vomiting and sometimes faints if she over eats, and also faints if she see a doctor injecting someone or things like that. she hasnt seen a doctor for it and i read on the internet its Neurocardiogenic syncope.

Her periods are also usually quite on time but this month it was 7 days early and she said she din bleed much and it lasted only for two days. Her periods normally lasts for 3 days but from past 2-3mnths its lasting only 2 days, is it because she is underweight? Should I be really worried about her weight? Please advice.. Thank you soo much in advance any advice you can provide.

Answer
Hello Jino,
Your girlfriend is very thin, and that's probably why her periods are light and short.  Some very thin women stop having periods altogether.  Her body mass index (BMI) is only 15.3.  A BMI under 18.5 is considered underweight.  I suspect that she has an eating disorder (anorexia or bullemia).  I think it would be advisable for her to see a doctor for this, ideally one that specializes in eating disorders.  Although she may seem healthy, eating disorders can be very bad for health over time.  Women with eating disorders think they're overweight, when it's obvious to everyone else that they're too thin.  I hope you can get her to see someone.  Best wishes.