Can there be too little body fat?

Question
I consider myself to be a very healthy 25 year-old woman.  I am a little over 5'6'', around 115 lbs., have a diet high in fruits, veggies, and whole grains, very low in fat, and exercise very regularly.  Perhaps too regularly.  I have eased up a bit and am now running about 10 miles a week, rollerblading about 13.5 miles a week, doing aerobics about 40 min. a week, and doing weight training about 3 times a week.  I figure I consume about 1,900 calories each day.  My main concern is that my menstration has ceased again.  
  Earlier in the year this happened, and my weight likely dipped below 110.  I gained up to 10 lbs. and started having periods again (2 regular cycles) and have stopped once again.  Are my eating and exercising habits really too stringent and detrimental to my fertility, or are they fine and something else may be to blame?  Others tell me I just need to stop exercising and eat more fat (in other words, gain weight), and while I do want to be fertile and healthy, I don't want to lose the tone and physique I've worked so hard for.  Please help!

Answer
Dear Julie,

Clinical and epidemiological studies have revealed that not only excess body weight but also too low  body weight may increase risks for diseases. There is a U-shape curve describing how body weight influences health including hormonal health weigh the lowest part of the curve being optimal weight and the "wings" belonging to both overweight and underweight. Actually, we should be talking about body fat not weight:

- A healthy male's body should be approximately 12 percent to 18 percent fat.

- In females the number is slightly higher; approximately 14 percent to 20 percent fat.

Download the calculators excel worksheet to estimate your body fat:
http://dietandbody.com/plan/measuring.html

Losing weight can be as bad as being overweight.
http://dietandbody.com/article1080.html

Lose weight and live longer. Does it Work?
http://dietandbody.com/article1052.html

1. Prev:Enough Fat?
2. Next:Is full cream sweetened condensed milk good for you?