A lot of parents turn to different nutrition therapies for their children. A new research review sheds light on whether they work.

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There's solid evidence that behavioral and educational treatments can help children with autism spectrum disorder. But at one point or another, many parents will also try some kind of nutritional approach too, whether it's supplements or a special diet. Do those approaches work—and is there any harm in trying them?

In a new research analysis published in Pediatrics, researchers from Vanderbilt University analyzed nineteen studies and concluded that there was little evidence to support popular therapies such as fish oil tablets or a gluten-free/casein-free diet (GFCF) for children with autism.

Though some of the studies showed improvements in areas like challenging behavior, communication, and language, others indicated no changes at all—or in one case, more improvement was seen with a placebo than with a supplement. Researchers say one major issue is that most of the studies are simply too small or too short. More and better research is definitely needed.

But just because the science isn't overwhelming isn't a reason to dismiss these strategies outright, says Naureen Hunani, RD, a pediatric nutritionist and feeding specialist in Montreal. She says there is anecdotal evidence that some nutritional approaches may work for certain kids. For instance, a GFCF diet can be helpful for children with autism who also have GI symptoms such as abdominal pain, diarrhea, and constipation.

In fact, Hunani tried a gluten-free diet for her own son about two years after he was diagnosed with autism. "After a few days on the diet, my son looked straight into my eyes and said 'Mommy, I feel better'. I was shocked," she remembers.

Within a few weeks, she saw a difference in his behavior too. "I noticed he was more engaged," she says. "His speech improved significantly, he seemed more focused, less withdrawn, and was interested in socializing. His daycare teachers and therapists all noticed these positive changes as well." To test whether the diet was really making a difference, they went back to their normal pattern of eating. Sure enough, his behavior regressed.

Before embarking on a special diet, it's best to work with a dietitian to make sure your child is getting the nutrition he needs, since you'll be cutting out food groups (like dairy) or large numbers of foods (such as anything containing gluten).

"Restricted diets are tricky, especially in children," says Hunani. "Most children on the autism spectrum are not able to make dietary modifications easily as they have rigid and limited diets." Some kids may only eat a handful of foods, she says—and those foods are often gluten-rich. Feeding disorders and selective eating are also very common among children with autism. If your child doesn't eat a wide variety of foods and doesn't accept new foods easily, working with a feeding therapist can help—especially if you start feeding therapy before implementing a new diet, to allow your child time to increase the variety of foods he'll eat, she adds.

In terms of supplements, vitamin B12, digestive enzymes, and omega-3 fatty acids are among the most frequently tried for children with autism. There is some evidence that children with autism may be lacking in omega-3 and that supplementation can help, says Hunani. But you should always get professional advice before starting your child on supplements. Even though they seem like a "natural" approach, some supplements can cause harm in large doses.

Sally Kuzemchak, MS, RD, is a registered dietitian, educator, and mom of two who blogs at Real Mom Nutrition. She is the author of The Snacktivist's Handbook: How to Change the Junk Food Snack Culture at School, in Sports, and at Camp—and Raise Healthier Snackers at Home. She also collaborated with Cooking Light on Dinnertime Survival Guide, a cookbook for busy families. You can follow her on Facebook, Twitter, Pinterest, and Instagram. In her spare time, she loads and unloads the dishwasher. Then loads it again.