I'm 17 and have been doing low carb for a year. I eat way healthier than I ever have in my life. I eat more fiber, more veggies, etc. Anyway, I haven't had any problems except for missed periods, which is normal for someone who has lost weight, especially teenagers.

It is not normal to lose to your period. The only way time most lose it when losing weight is if they go below their set weight. Judging from your stats you are not underweight. Please talk to your doctor, amenorrhea is a strong indicator of malnutrition and severe calcium loss. Trust me, you don't want to find out that at age 20 your already have osteoporsis.

Excessive exercise along with dieting can cause missed periods too, especially among atheletes. I was on an AAU synchronized swimteam when I was young and missed and irregular periods were common among my teammates. 30 years ago, we didn't know what all that exercise and dieting could lead to. We were encouraged to look like gymnasts of the day, flat chested and no shape.

However, I missed my periods when I was a teenager because I had PCOS. If I'd known to low-carb then, I might have saved myself a lot of grief.