Here is the theory of the gluten and casein free diet:
"Gluten and casein are getting a lot of attention in the autism community and from doctors in the "Defeat Autism Now!" biomedical movement. Some parents, doctors and researchers say that children have shown mild to dramatic improvements in speech and/or behavior after these substances were removed from their diet. Some also report that their children have experienced fewer bouts of diarrhea and loose stools since starting a gluten-free, casein-free (GFCF) diet. Author Donna Williams, who has autism, says she has been helped by "nutritional supplements together with a dairy/gluten-free and low Salicylate diet." (Salicylates are found in some fruits likes apples and other foods). Some people report no benefits from the GFCF diet.
Casein is a protein found in milk and foods containing milk, such as cheese, butter, yogurt, ice cream, whey and even some brands of margarine. It also may be added to non-milk products such as soy cheese and hot dogs in the form of caseinate.
There is growing interest in the link between autism and gastrointestinal (GI) ailments. A study by the University of California Davis Health System found that children with autism born in the 1990s were more likely to have gastrointestinal problems, including constipation, diarrhea and vomiting, than autistic children who were born in the early 1980s. Some people use the GFCF diet mainly to ease gastrointestinal problems and food allergies or sensitivities.
According to one theory, some people with autism and PDD cannot properly digest gluten and casein, which form peptides, or substances that act like opiates in their bodies. The peptides then alter the person's behavior, perceptions, and responses to his environment. Some scientists now believe that peptides trigger an unusual immune system response in certain people. Research in the U.S. and Europe has found peptides in the urine of a significant number of children with autism. A doctor can order a urinary peptide test to see if proteins are being digested properly.
Studies are underway to examine the effectiveness of the GFCF diet, which has not gained widespread acceptance in the medical community. One recent study found behavioral improvements in children on a GFCF diet, while another study found no significant effects from the diet.
Medical tests can determine if your child has a sensitivity or an allergy to gluten, casein and other foods such as eggs, nuts and soybeans. Any pediatrician or a physician from the Defeat Autism Now! list can order these tests before you begin the diet."
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Hope it helps!