It is quite a controversial topic...
Here are the results from a recent study conducted by INCA - Impact of Nutrition on Children with ADHD:
Their conclusion was that "A strictly supervised restricted elimination diet is a valuable instrument to assess whether ADHD is induced by food."
Does Diet really affect ADHD symptoms? Everyone has got their own thoughts and theories...
All I know is what I have experienced with my own son who was diagnosed with ADHD and I would say that it definitely made a difference for him.
Let's take a trip down memory lane... it's first grade and my son is having daily issues at school - he can't sit still, he can't focus, he is easily frustrated and melts down quickly when things don't go his way. He has regressed and is hiding under his desk when things don't go as expected. He is exhibiting behavior that clearly illustrates that he feels like everyone is against him. When something happens, he immediately moves into a "fight or flight" type reaction and is unable to reason or logic through any situation until he is given time to calm down. He is being suspended for his behavior in the classroom and no one at school is able to help us. We did want any desparate parent would do, we scheduled an appointment with the psychiatrist to get some answers. Originally it was not clear if the behaviors were related to ADHD or just anxiety or a combination of both. We tried anxiety meds first, but that didn't quite solve the problems... so we tried ADHD meds instead, but that didn't quite solve the problems either. We ended up using meds for both anxiety and ADHD and that seemed to be the magic combination for my son at the time. We had no reason to believe that he had food allergies or sensitivites at this point.
Then my sister was diagnosed with a number of food allergies and in a quest to find a cookbook for her, I ran across a special cookbook for kids with ADHD. As I started to research this diet and the science behind it, it made sense to me. I started seeking out recipes and ran across several Yahoo groups and several wonderful blogs of parents who were already doing the diet and sharing all their converted recipes. I decided it was worth a shot to give it a try and so we started by eliminating gluten & dairy from my family's diet. I located a doctor in our city who was helping parents with this type of intervention for kids with ADHD, Asperger's and Autism and with his help, we discovered additional food allergies/sensitivities and eliminated all known problem foods. As part of this we also began making all our food at home which removes all the processed foods, preservatives, food colorings, etc. which can also cause problems for many kids today.
Fast forward back to the present... my son has been on his special diet for 2 and 1/2 years now and it isn't very complicated, it has become second nature to cook differently and our entire family is healthier because of it. We make most of our own meals at home which saves us alot of money on eating out. We had taken my son of both of his medications the summer between 2nd and 3rd grade and he was doing well without them. My son ended up transferring schools this year due to a change in school boundaries and I think the stress of the changes affected him. We ended up taking him back to the psychiatrist because we were seeing some of those old behaviors and the doctor said it sounds like his anxiety has relapsed. We started him back on anxiety meds and he is a different child. His teacher is amazed at the change in him at school and I no longer get daily communications regarding problems from the teacher. The interesting thing is that he is not exhibiting the significant focus issues that he had in 1st grade. He is on the same anxiety med as back then, but there is no need for the ADHD stimulant medication this time. He is able to focus and complete his work at school. The only difference now is his diet.
When we were first starting out with the food allergy/sensitivity discovery, I read a book that I highly recommend to any parent contemplating a change in diet. Healing the New Childhood Epidemics: Autism, ADHD, Asthma, and Allergies by Kenneth Bock. Doctor Bock explains the science behind the food sensitivities and how it can affect our children and their behavior.
If you are thinking about taking the plunge and trying a removal of gluten & dairy from your child's diet, I highly recommend the book The Autism & ADHD Diet: A Step-by-Step Guide to Hope and Healing by Living Gluten Free and Casein Free (GFCF) and Other Interventions by Barrie Silberberg. I wish I had this book when I first started, it would have made my life alot easier.
With that all being said... I do not believe that diet is the ONLY thing that has helped us overcome the focus issues. He has gone to countless OT appointments to help with many different challenges. We have done Brain Integration Therapy which has helped in certain areas. We have done biofeedback. He receives assistance at school through interventions as needed. We are also supplementing key things that we found him to be low on like Vit D, B12, and Folate. Overall we have done many different things to help him be successful at school and home and his diet is just one piece of the puzzle. As parents of kids with ADHD, we have to have alot of different tools in our toolbox, and this is just one tool that I find useful in helping my son.
I encourage you all to do your own research and decide for yourselves if diet will help your child. There are several different diets that can benefit ADHD symptoms. The one advice I would give is, don't give up too soon! If at first it seems that the diet isn't working, stick with it for several weeks and allow them to rid their systems of all the things that were causing a problem before you decide if it is working or not. Sometimes things get worse before they get better - kind of like an addict going through withdrawls. Keeping a food journal is also very helpful. Remember it can take 24-72 hours to see behavioral effects from a food that is eaten and with a food journal it will be easier for you to track down any behaviors related to food. Best of luck and let me know if you have any questions!