Mental disease mocks our manners and parodies our social values in the distorted mirrors of madness. Eating, especially, offers food for thought about normal behavior. Nowhere is this more evident than in a mental disease called anorexia nervosa.

Predominantly an illness of pretty, bright, and rich adolescent girls, anorexia nervosa is characterized by excessive dieting and loss of weight, which leads to dangerous infection and occasionally death. While its victims live on self-imposed diets that can lead to starvation, they devour attention, and that - it seems - is their unconscious purpose.

In our carbohydrate-conscious culture, it is difficult to know just when someone slips below the working weight of the stylish woman with hollow cheeks in the pages of Vogue. Sufferers of anorexia nervosa, nevertheless, make Twiggy look like the fat lady of the circus. By the time they see Dr. Hilde Bruch, professor of psychiatry at Baylor College of Medicine in Houston and a specialist in the disease, they weigh, typically, about 65 pounds. If they refuse to gain weight by eating, and many do, they must be fed intravenously before they can begin the find the causes of what Bruch calls their "relentless pursuit of thinness."

Anorexia nervosa means a nervous lack of appetite, but actually those afflicted with it are preoccupied with food. Many frequently go on eating binges and make themselves throw up afterward. What begins as a simple desire to lose weight becomes a moral mission. Self-denial and discipline become the ultimate virtues. Like ascetics, whom they usually resemble in appearance, sufferers condemn any satifaction or pleasure derived from the table as a shameful form of self-indulgence.

The disease probably would hold little popular interest if it were as rare today as it was a century ago when it was first described by British physician Sir William Gull. According to Bruch, who specializes in treating many different kinds of eating disorders, its increase during the past 20 years could be considered an epidemic except that "there is no contagious agent." Instead, growing social pressures compound the psychological problems.

Fashion, movies, magazines, radio and television all carry the same message: "One can be loved and respected only when slender." Bruch's patients believe that more is less. No matter how slim, they see themselves as "too fat." Greater sexual freedom also may be a factor, particularly when liberation is perceived as a demand. Bruch says that a teen-age girl "who doesn't date feels, or is treated as if she were on the fringe. Often anorexia appears after a film or lecture on sex education which emphasizes what she should be doing but is not ready to do." Anorexics are afraid, if not overwhelmed by the choices confronting an active, healthy teen-ager, and they recoil from adult female roles. The disease retards or stops menstruation and breast development.

Anorexia nervosa, like gout, usually strikes the financially fortunate. In a recent survey in English private schools, one girl in 200 was found to be suffering from it; yet only one case in 3000 students was found in the English free-school system. Prosperity appears to be part of the problem.

Ida - whose case gave the book its title - is a sad example. She describes herself as a sparrow in a "golden cage," too plain and simple for the luxuries of her home, but also deprived of the freedom of doing what she truly wants to do. Golden cages are for big colorful birds to show off their plumage, she says. By comparison, she is an energetic sparrow who wants "to take off on its own." Ida compromises. she takes off weight. Senior year in high school she reaches a nadir of 63 pounds.

Many anorexics express themselves as Ida did, Bruch writes. "Their whole life has been an ordeal of wanting to live up to expectations of their families, always fearing they were not good enough in comparison with others, and therefore, disappointing failures." They lack control over their lives, but not their bodies. Before they diet, many of them are model children, sweet, compliant - what they later recall in therapy as "the great put-on," academy-award performances for parents. When they develop anorexia they speak of being split into two people, one of whom is "the little man who objects when I eat." Prevention of the disease, says Bruch, requires that parents and teachers recognize "pleasing superperfection" as a "sign of inner misery."

There is no easily identifiable family portrait for the anorexic patient, but their parents, Bruch says, "tend to present family life as more harmonious than it actually is." Because the development of the disease is closely related to abnormal family patterns, she says, "successful treatment must always involve resolution of the underlying family problems."

Bruch criticizes "outmoded concepts of psychoanalytical treatment" which stress symbolic and unconscious attitudes about food, as well as behavior modification methods which reduce the problem to a learned response and simply offer rewards and punishments as a means for changing an anorexic's eating habits. She believes that individual psychotherapy and a weight program in cooperation with the psychiatrist, is the treatment choice. Family therapy works sometimes, she says, but well-informed and open-minded parents will get therapy on their own.

Bruch's evidence, based on personal experience, is persuasive. But it is far from conclusive, and she concedes that more detailed information is needed. Despite continuing research at the National Institutes of Health, in many ways anorexia remains an enigma.

Though "The Golden Cage" is written primarily for clinicians, researchers, parents and teachers who see "skinny kids" like those whom Bruch treats, the book is likely to fascinate and move any reader who has struggled with a calorie counter and who has, with guilty fingers, found the bulge in the flesh even before the tongue has had time to savor the taste of the tart.