Malabsorption syndromes can cause significant weight loss and loss of appetite, so diagnostic testing for these syndromes is essential before a diagnosis of AN can be reached. Many of these disorders will present with only vague symptoms, and may be overlooked by the attending physician.
I have spoken with several AN patients who insist they are sticking with their high-calorie meal plan, but are unable to gain weight. It is not uncommon for therapists to simply assume that the patient must therefore be inducing vomiting after eating. The patient generally is not trusted to tell the truth, so they are often accused of lying about this. Some are told they have a "racing metabolism", or that they must be burning off the calories by exercising secretly.
Malabsorption can be the result of a broad spectrum of diseases. Typically, malabsorption can be the failure to absorb specific sugars, fats, proteins, or other nutrients, or it can include a general nonspecific malabsorption of food. Diarrhea (sometimes alternating with constipation), bloating or cramping, failure to thrive, frequent bulky stools, muscle wasting, and a distended abdomen may accompany malabsorption.
Malabsorption can affect growth and development or can lead to specific illnesses. Some of the causes of malabsorption include cycstic fibrosis, celiac disease, Whipple disease, lactose intolerance, Shwachman-Diamond syndrome, bovine lactalbumin intolerance, soy milk protein intolerance, acrodermatitis enteropathica, biliary atresia, abetalipoproteinemia,diphyllobothrium latum (tapeworm) infestation, bovine lactalbumin intolerance, juvenile pernicious anemia, giardia lamblia (beaver fever) infestation, strongyloides stercoralis (threadworm) infestation, necator americanus (hookworm), Crohn's disease, bile duct obstruction, amyloidosis, lymphoma, biliary cirrhosis, and many others. Some of these disorders are rare, while others are quite common. For an excellent article on malabsorption syndromes, click here.
The human digestive tract is extremely complex, and a lot can go wrong. Knowing this, the importance of diagnostic testing cannot be ignored. Due to the minimal amount of diagnostic testing done by many eating disorder programs, there is a high probability that a significant number of patients diagnosed with AN actually have some malbsorption syndrome as an underlying cause of their weight loss. This cannot be determined without appropriate diagnostic testing. Even if the patient started out dieting or exercising to lose weight, it should never be assumed that excessive weight loss is due to mental illness. Treating malabsorption syndromes with psychotherapy can have disasterous results.