A lot of people with anorexia (it's estimated to be about 80%) have issues with exercise and hyperactivity. Some of it is a psychological need to burn calories and lose weight; other parts of this hyperactivity are biologically driven. When rats are deprived of food, they run incessantly on their wheels. I highly doubt the rats are worried if their tails make their butts look fat.

This kind of excessive, compulsive exercise has HUGE damage on the body. It can cause the Female Athlete Triad, characterized by eating disorders, amenorrhea, and osteoporosis. But those are signs and symptoms, not causes. And by the time you see many of these signs, there can already be irreversible damage. I lost my period for only about 9 months, and still developed osteoporosis (which was diagnosed at only 5 months without a period).

Recent research has looked at the role of leptin* in not only appetite, but also in activity-based anorexia. What researchers found was that the lower the leptin levels, the greater the hyperactivity. And since hyperactivity is associated with a poorer outcome in anorexia, finding ways to treat this symptom could help improve the typically dismal recovery rates for chronic patients.

One obvious solution is to treat hyperactivity with leptin. In an animal model of activity-based anorexia, leptin treatments did decrease hyperactivity. Except low levels of leptin are correlated with decreased appetite. Ultimately, the rats still had a negative energy balance Translation: they burned more calories than they ate.

Whoops...

On a more uplifting note, other research has shown that leptin levels normalize with the restoration of a "normal" body weight. Where "normal" here equals the body weight determined by your DNA, and not some formula**. The use of olanzapine (brand name Zyprexa in the US) has been shown to decrease hyperactivity and hence improve the ability to reach a normal body weight. It did help calm the obsessive thoughts in me, only it helped trigger my seizures. Alas.

All of these experiments and discoveries are interesting and crucial (at least to me) in teasing out the causes and effects of anorexia and the malnutrition it causes. However, the most promising treatments are olanzapine, eating a proper level of calories whether you feel hungry or not (when underweight, low levels of leptin mean you feel much less hungry), and prevention of hyperactivity. Some level of activity can help with anxiety. I took brief walks with my mom every day, which was both nice to get outside and relax, as well as have some uninterrupted Mommy-Daughter time. But I also had to make up for the calories I was burning, and as long as my weight remained stable, I was approved for walking.

Because hyperactivity is so biologically driven, so much support is needed to overcome these urges. They're not your fault. And you can overcome them, but you need lots of support.

*Fun factoid: leptin is secreted by adipocytes, a fancy name for fat cells. So as body fat percentage decreases, so does leptin production and secretion. Which enables the sufferer to lose even more weight, and a vicious cycle ensues.
**The formula of 100 lbs for a woman 5 feet tall, and adding 5 pounds for each inch over 5 feet would leave me underweight and batty.