This is an open access study so the text of the study is available for you to read.
The authors of this study conducted a systematic review that looked into the question of how safe and effective Omega-3 fatty acids are for treating autism. This is one of the most commonly used alternative therapies used for children with autism (28.7% of children).
The mechanism of how Omega-3 fatty acids would improve the symptoms of autism is unknown but it is thought that some of the fatty acids (DHA) are essential to the growth and development of the human brain. They are also known to have an anti-inflammatory effect.
There have been some some studies that have reported a low level of Omega-3 fatty acids in children with autism when compared to controls as well as other studies that have reported deficiencies in individuals with other psychiatric disorders such as schizophrenia and ADHD.
The authors' review found a total of 143 potential articles of which 6 were considered robust enough to be included in the analysis.
Of these four were open-label studies that showed some potential benefits but all suffered from missing data, methodological flaws, or other problems that rendered them of little use.
One of the articles was a case report of an 11 year old child with autism whose anxiety and agitation were successfully treated with omega-3 supplements. However, case reports being what they are, this article provides little information.
The final study was a randomized controlled trial of 13 children with autism. This study showed some improvements between the treatment and control groups but none of the improvements were statistically significant.
The authors concluded that while Omega-3 fatty acids are relatively safe there is insufficient evidence to say whether they are beneficial in the treatment of autism - but since this is such a commonly used therapy there needs to be more research done in this area.
I would like to point out two very good sections in Appendix 2 of the study that attempts to answer the following questions concerning alternative (CAM) therapies for autism
How do I decide whether to try a CAM therapy for my child who has an ASD?
How do I evaluate the scientific evidence of CAM therapies?
Since this is an open access study you can go read the sections for yourself - they start on page 8 are are worth the time to read. However I am going to copy the last paragraph from the second question because I think it is a very important point that tends to get lost in all of the discussions out there:
For the vast majority of CAM therapies for ASD, there is little or no evidence to document efficacy. However, the lack of evidence should not be equated with a conclusion that a therapy is ineffective. In the absence of scientific evidence, there is an equal chance that any therapy will be beneficial or harmful.