Researchers gathered meta-analyses of double-blind, placebo-controlled trials in children who met the criteria for ADHD. They found fourteen such reviews and kept six that fit their rules. Two looked at removing artificial food colors, two at a few-foods diet, and two at supplements of poly-unsaturated fatty acids.
The few-foods diet, which strips the diet down to a small list of foods, had the strongest results. Its effect sizes ran from medium to large (0.51 to 0.80). When parents rated their children's behavior, the effect was large (0.80).
Removing artificial food colors had a smaller effect (0.08 to 0.44). Fatty acid supplements had the weakest results of all, close to nothing (-0.05 to 0.17), with a small effect when parents and teachers rated behavior (0.16). The authors judged these two too small to help much with ADHD.
The authors note some limits. They searched only two databases and only published reviews, so some work may have been missed. The diet results may apply only to families open to trying a diet.
Anyone considering a diet change or a supplement for a child should talk with a clinician about their own situation.
Source: Pelsser L, Frankena K, Toorman J, et al.. Diet and ADHD, Reviewing the Evidence: A Systematic Review of Meta-Analyses of Double-Blind Placebo-Controlled Trials Evaluating the Efficacy of Diet Interventions on the Behavior of Children with ADHD. PLOS ONE (2017). doi:10.1371/journal.pone.0169277