The newest recognized eating disorder is actually not yet medically classified as diagnosable in the classic psychological diagnostic manual (The DSM). Then again, bulimia wasn't officially classified until the 1980's. Orthorexia is a disordered type of eating where the person focuses on avoiding foods and ingredients they believe are bad for them.
In a balanced life, people enjoy foods they like to eat and limit foods that aren't good for them. Some people, of course, eat what they like regardless of whether it's good for them or not. People with orthorexia do not see food as something enjoyable. They eat because they want to be nourished. They avoid certain fats or additives or food components because they want to be healthy. Ironically this condition leads to poor health in many ways.
Some foods are excluded to the extent that the person may suffer a deficiency of fat, protein, vitamins, or minerals. Usually too much weight is lost and the person suffers some degree of malnutrition. Emotionally, much of the person's time is spent figuring out what to eat, reading labels, reading about the latest "bad" food and feeling near phobic about ingesting something they view as toxic.
Their social life is affected because they can't eat in restaurants and they can't eat what other people might be serving. They become obsessed with healthy eating to the point that it's not healthy anymore.
Signs that someone is orthorexic include focusing hours a day on purchasing and planning meals, staunch avoidance of certain classes of foods (eg, no fat, or no dairy, or no processed food, or no additives), obsessively reading labels, and often having the same food every day for each meal. For example it would be common to hear someone say, "I have whole grain cooked hot cereal for breakfast with rice milk, organic yogurt and carrot sticks for lunch, grain-fed chicken with brown rice for dinner, and an apple or rice cake if I want a snack". At first glance this may sound healthy, but the diet is actually quite low in calories (less than 800), low in protein (less than 45 grams) and almost devoid of fat and vitamin C.
It is unfortunate that the initial goal to be healthy actually leads to health problems in many of these people (more commonly they are women, as is true for other eating disorders as well). If you or someone you know fits some of this description it's important to find a trusted health professional to speak with. You can get back on the right track and get your health back!