Amenorrhea?

I'm 16, female, 5'5", 134 lbs, and have been on maintenance for about two months now. According to my measurements, I have about 19.5% body fat, and a small frame. I eat an average of 2000 calories a day, but this varies wildly, usually close to 3000 on the weekends and 1300 on the week days. I also walk at 4.4 MPH six days a week for 95 minutes on a variable surface.

But whenever my weight approaches 135 or so, I lose my period. I haven't had it since March, when I finished taking off 15 Christmas pounds. The same thing happened last year, too; when I got to 135, I lost my period for eight months, and got it back when I gained weight after vacation.

Why has this happened? I've had my period since I was 11 years old; I'm at a rather high BMI for my height and age. It doesn't make any sense.

Thank you in advance for any advice you can give me.

~Sam

Your body fat percentage dips too low. You need a certain amount of body fat to produce estrogen.

I'd agree with the previous poster. Obviously you have a fair bit of muscle if your body fat percentage is 19.5%, and it's a lack of body fat rather than purely BMI which affects your ability to have a period. Losing your period is definitely a sign that something isn't right with your body, so you might want to talk with your doctor about it.

You should talk to a doctor about your concerns.  There are a lot of other reasons why a female body can stop menstruating besides body-weight.  Too-low body fat, a poor diet, stress and overexercising are just some.  And there are also various illnesses that can affect fertility.

To be on the safe side, don't self-diagnose or use internet message boards go to see the professionals.... a doctor.

As an alternative to traditional medicine, I recommend checking out an Arvigo Mayan Abdominal Massage practitioner.  http://arvigomassage.com/practitioners_list.p hp

I've experienced Amenorrhea a couple of times over the past decade, for different reasons, and found that my practitioner's approach was very gentle, natural, non-invasive. In addition to the reason's gi-jane mentions, on one occasion, my uterus was displaced due to a fall, which was causing the amenorrhea. Through abdominal massage and herbal teas/tinctures, she was able to support my body to get back on track rather quickly.  It was amazing, actually. She also taught me some self-care techniques which I practice to this day. 

Additionally, a friend of mine was scheduled to have a hystorectomy a couple of years back. I recommended she see my practitioner first just to see if there was anything she could do. She was able to get her back on track, much to her Doctor's surprise, and she was able to avoid the hystorectomy.

Good luck.