Some believe that an overgrowth of the yeast Candida albicans (which naturally occurs in the body) can damage the intestines of children with autism.

Photo courtesy CDC/Dr. William Kaplan

Food Allergies and Leaky Gut Syndrome

There are a couple of different theories as to why children with autism can benefit from a diet free from gluten and casein. One draws a connection between food allergies and behavioral problems. An allergy is essentially an extreme inflammatory response by the immune system to a substance that it sees as an invader. Allergies can manifest in a wide variety of physical symptoms, including diarrhea, vomiting, hives, wheezing and rashes.

Children with autism often have trouble communicating, so they may not be able to tell their parents that they're experiencing painful symptoms like acid reflux and stomach cramps. Instead, they scream, act aggressively and throw temper tantrums. The discomfort, pain and other physical reactions from the allergic response could trigger autistic behaviors.

­Another theory states that many children with autism have a "leaky gut," also known as increased intestinal permeability. This theory suggests that autistic children have tears and holes in their intestinal walls, possibly due to damage from toxins, antibiotic sensitivity or infections (such as an overgrowth of the yeast Candida albicans). In addition, these children may lose healthy digestive bacteria and have damage to the cells that produce enzymes needed to absorb certain proteins (such as gluten) properly.

Both leaky gut and problems with absorbing specific proteins, the theory goes, can cause intestinal contents to enter the bloodstream. This not only includes toxins and bad bacteria, but also protein molecules that haven't been fully digested. The latter may actually lead to food allergies because the immune system treats the molecules as foreign matter. It can also lead to what some autism researchers call the opioid effect.

Proponents of the leaky gut theory believe that the partially digested protein molecules from gluten and casein, also known as peptides, can reach the brain via the bloodstream. Peptides have a molecular structure similar to that of your brain's natural opioids (endorphins), so they're drawn to the brain's opioid receptors. This leads to problems with behavior, speech and social skills. Just as opioid drugs such as heroin are addictive, so are foods high in gluten and casein for children with leaky gut.

Some autism researchers have tested the urine of these children and found high levels of these peptides, which seem to support the leaky gut syndrome theory. Researcher Dr. Paul Shattock has drawn a connection between escalating levels of peptides and the most severely impaired autistic children [aource: McCandless]. However, a March 2008 study published in the Archives of Diseases in Childhood by British researchers found that children with autism didn't have a higher level of peptides than those who did not have the disorder.

Many doctors don't believe that leaky gut syndrome exists. Some children with autism do have food allergies when tested, but not all. But for their parents, some don't mind that there's not science-based evidence to back up the autism diet. What matters is that it worked for their child. We'll look at exactly what a gluten-free/casein-free (GFCF) diet entails, as well as avoiding salicylates and other foods, next.