Gluten turns up in the most unlikely places. In 2006, McDonald's was sued because it hadn't informed the public that gluten and casein were used to make its french fries.

Scott Olson/Getty Images

Gluten-free, Casein-free Diet

A 2008 survey conducted by the Autism Research Institute showed that out of the 2,500 cases in which a gluten-free, casein-free (GFCF) diet was used in the treatment of autism, 66 percent of children showed improvement. Fifty-two percent of the more than 6,300 cases in which parents just eliminated casein also got better. However, not all children with autism experience benefits from special diets.

It's pretty challenging to avoid all gluten and casein, and it's important to discuss any dietary changes with a doctor. Most parents begin with removing casein, which is easier to do. Going on the full GFCF diet is generally a slow process that involves eliminating one food at a time, and most believe that the child should be casein-free for about a month to see if there are improvements. Once gluten is removed, the trial period should last at least four months.

Removing all casein and gluten from a child's diet means paying a lot of attention to ingredient lists. The obvious foods containing casein include milk, all forms of cheese, yogurt, ice cream and butter. However, it can also be found in cookies, hot dogs, vitamins, cream soups and salad dressing. If the ingredient list includes casein, caseinate, sodium caseinate, lactose or whey, then it's not allowed on a casein-free diet.

Gluten is even more prevalent. In addition to being in anything made with wheat (bread, crackers, baked goods, pasta), it can also be found in other grains, such as rye, barley and oats. Soy sauce contains gluten, and so do hot dogs, lunch meats, seasonings and spices, licorice, tea (if the tea bags are sealed with wheat paste) and a host of other prepackaged foods. Gluten is even used in nonfood items like toothpaste, lip balm and lotion, so parents must read those labels, too. Those who have gotten positive results from the diet stress the importance of eliminating all casein and gluten and claim that accidental slip-ups have resulted in a return of autism behaviors.

So what do children on GFCF diets eat? There are lots of gluten-free foods available in grocery stores and health-food stores due to the numbers of people with celiac disease, an autoimmune disorder affecting the small intestine that results from a reaction to a specific type of gluten. Most children on these diets eat a lot of lean protein, fruits and vegetables.

Although the GFCF diet is the most common autism diet, some parents take it a step further and remove other foods as well. Those who believe that yeast overgrowth can cause autistic behavior restrict sugar intake because sugar is food for yeast and encourages its growth. The yeast-free diet prohibits any fermented foods (such as vinegar) as well as any foods that may contain molds, like mushrooms.

Other diets may remove artificial colorings, flavorings and preservatives because they can contain salicylates, a plant compound also found in some fruits. The connection between artificial colorings, flavorings and preservatives and behavior disorders isn't new; a similar diet has been used to treat children with ­ADHD since 1979 (and has also been controversial).

For a more in-depth look at autism, related disorders and the issues surrounding it, try the links on the next page.