Physiology & Behavior, 135 (2014), 174-179.
SULT1A inhibitors in foods, including natural substances and artificial food colors, have a role in ADHD that can both worsen or improve symptoms. … SULT1A inhibition can influence brain catecholamines through the intermediary of plasma tyrosine levels, which are influenced by dopamine inhibition of intestinal tyrosine hydroxylase.
Note: SULT1A is an enzyme also known as PST. This is a complicated study for those without an organic chemistry background, but it basically gives a clue why some children appear to get worse when first put on the diet.