There’s a lot written about nutritional treatment for ADD ADHD. A lot of it seems to me to be wishful thinking. Here’s some science, from Dr. Farone. I’ve edited his post.
More recent meta-analyses of omega-3 fatty acids suggest that they show some efficacy, about half as much as stimulant drugs. Those with a high EPA/DHA ratio seem to have the best effect.
Using a standardized measure of treatment response effect where 0 means the treatment does not work and higher numbers are better. For stimulant drugs, the effect is 0.9, for food color restrictions it is about 0.5 and for other elimination diets it is about 0.4. Because most of the food color studies focused on kids with high levels of food colorant intake, the overall effect is smaller. The effect for other elimination diets is not reliable. A key issue is that the elimination diets are not easy to implement.
To to my surprise, there are a few people for whom the color additives make a difference. Please note that one of my son in laws takes a handful of “natural” pills and swears that they help his ADD ADHD.