21 year old female hasn't had period in months

@melissa123
You mentioned few things that might be reason, low body fat and excess exercises. The condition is called amenorrhea.
Here is article on:
https://www.mayoclinic.org/diseases-conditions/amenorrhea/symptoms-causes/syc-20369299
Is she just seeing her primary provider? She may want to seek advice from a gynecologist.

@melissa123
I would encourage her mother to consider getting a mental health specialist for her daughter. It is concerning that she is on an elliptical machine so long and doesn’t eat much. It sounds like an eating disorder and unhealthy obsession with excessive exercise/body image.

She may also want to see her gynecologist to get an abdominal and transvaginal ultrasound to make sure everything appears normal.

Her primary doctor may want to look more closely at her thyroid to ensure it is functioning properly.

@melissa123 It's so kind of you to bring your concern about your friend's daughter here. Is the mother also concerned?

I agree with the recommendations of @dlydailyhope and @roch. Spending 3 hours on an ellipitical is excessive exercise and then the report of the restricted diet leads me to think the daughter is experiencing problems with her body image and perhaps an eating disorder. I've read many accounts of female athletes such as gymnasts, x-country skiers, and runners who experience amenorrhea but it does not sound like this young woman is in training for a sport. Is that correct?

The place to start is with the primary care doctor. Since the daughter is 21-years-old she is an adult and so the mother cannot bring the daughter to an appointment as she might with a young child.

Have you discussed these recommendations from the members here with your friend?

This is exactly true. She has an unhealthy relationship with food and exercise. She is seeking mental health and going to a doctor for this. They didn't find anything from the bloodwork. I think its her diet and excessive exercise.

No you are completely correct. Definite body image issues. Her mom is getting her help but it's difficult. She is an adult.

@melissa123 My understanding is that body image disorders and eating disorders are difficult to treat. I know a few people who needed to be hospitalized and go through inpatient treatment. If this were my daughter I would be very frightened but ultimately it will be up to her daughter, as an adult, to make the decision for treatment. And if the daughter does not want treatment? What support groups are available in your area for the family members because the mother may need her own source of support?

Here is what I know. I have an extremely healthy daughter who is now 36. She has been a runner and a soccer coach since she was a teen. She runs maybe 8 to 14 miles a day after her day job as a social worker and right before she goes to soccer. She doesn’t eat much in the day at work except snacks like a protein bar or some addictive favorites that aren’t good for her( goldfish and DOTS pretzels). She drinks a ton of water! Her bloodwork is perfect! She hasn’t had a period since probably before she was 21. If she ever gets one she wouldn’t probably have more than a spotting. Like you I worry because girls who don’t get their periods are more likely to develop bone issues later in life. We have periods for a reason. I think it is unlikely it would interfere with your daughter’s ability to have a baby . As a child I was not a runner but didn’t get my period very often most likely because I didn’t eat well, and I got married and had four biological children. My daughter is adopted from a Chinese orphanage. Bottom line I wouldn’t worry about the baby thing - but the bone thing is a concern ! Irene5

it's my friends daughter. Yes I'm sure her mom is worried. The doctors didn't seem to have an answer. I just thought it was her eating and excessive exercise.

And you are probably correct. Your friend might want to take her to a nutritionist to make sure she is consuming enough calories . As for my adopted daughter, she is like Mary Poppins - practically perfect in every way:). Her BMI is fine - I believe. Her doctors aren’t concerned. Often young girls exercise and don’t eat a lot and develop anorexia which clearly is not good and involves not having a period as well. . But runners do typically have light periods or none at all. One of my own biological children was a runner but became anorexic. As her mom I did not know she had issues other than wanting to be fit. . Not having a period is one thing - not eating enough is something else entirely. Tis a fine line. Your friend has a right to be concerned. A nutritionist is a good place to start. Life can be hard for some girls, and they are good at keeping secrets. Irene 5

I had a similar situation at your daughter's age. Working out, no period, very careful what I ate, on and on. Ended up I was full of large fibroid tumors on my ovaries for years. I was diagnosed 10 years after the amenorrhea started. The gyno that I had then never picked them up in the pelvic exams that I went to every year. This doctor retired and my new gyno found them on the first visit. This may be something to check.