The research, published in PLoS One, reveals a higher rate of seizures among children with autism who were fed infant formula containing soy protein when compared to milk protein.
Led by Cara Westmark from the University of Wisconsin-Madison, USA, the team explained that the investigation was sparked by mouse studies of a drug that, it was hoped, would inhibit seizures by blocking signals that excite nerve cells.
"It was pure serendipity that we happened to look at soy," Westmark noted.
Findings from an initial study on mice led the team to investigate the links between soy and seizures in a group of nearly 2,000 infants fed either dairy or soy based formula.
The findings showed that children with autism who were fed soy formula had 2.6 times as many febrile seizures as the children fed non-soy formula in the database. That means 4.2% of the soy group had a seizure associated with a fever, compared to 1.6% of the dairy group, said the team.
"Soy is a widespread ingredient in many food products and 25 percent of infant formulas are soy based, so this is something that needs to be studied," commented Westmark - who noted that the results of the study do not mean that autistic children who eat soy-based formula are going to develop seizures, and that the vast majority of infants in both dietary groups did not have seizures.
From mice to humans
The team's interest in soy and seizures came after they tried to simplify the initial mouse study by replacing the standard lab chow, which had a variable composition, with a diet containing purified ingredients. Unexpectedly, that diet reduced the rate of seizures by 50% compared to standard chow, said Westmark.
"We were intrigued that a dietary alteration was as effective as many medicines in reducing seizure incidence and wanted to pursue that finding," she explained. "We found that the main difference between the diets was the protein source. The standard diet was soy-based, while the purified diet was casein, or dairy, based."
Westmark then began to look for the effect in people, and decided to focus on infants who may consume nothing but formula. Knowing that people with autism have a higher rate of seizures, Westmark turned to a database from the Simons Foundation Autism Research Initiative (SFARI).
Using the SFARI database, the team analysed data from 1,949 children fed either soy-based of dairy-based formula.
"There was a 2.6-fold higher rate of febrile seizures, a 2.1-fold higher rate of epilepsy comorbidity and a 4-fold higher rate of simple partial seizures in the autistic children fed soy-based formula," revealed the team.
"No statistically significant associations were found with other outcomes including: IQ, age of seizure onset, infantile spasms and atonic, generalized tonic clonic, absence and complex partial seizures," they added.
The team also noted that the soy-seizure link reached borderline significance among boys, who comprised 87% of the children described in the database.
Westmark added that while the study has shown an association, there must be further clinical work to be sure of causation.
"We can say that we have a potential association between the use of soy-based formula and seizures in autistic children; we can't say that this is cause and effect," said Westmark.
"We were fortunate to be granted access to the SFARI database, but it was not set up to answer the questions we were asking."
Source: PLoS One
Published online ahead of print, doi: 10.1371/journal.pone.0080488
"Soy Infant Formula and Seizures in Children with Autism: A Retrospective Study"
Author: Cara J. Westmark