Attention Deficit Hyperactivity disorder (ADHD) is a disorder that starts in early childhood it includeshyperactivity, inattention and impulsivity. In Australia the government has suggested new guidelines for treatment of this distressing disorder which can continue into adulthood.
Drugs given to treat ADHD have serious side effects
The concern is that drugs given to treat ADHD have serious side effects. Instead of reaching immediately for drugs to help the child the recommendations in Australia are to look at other approaches including changes in nutrition, behavioural management, education, and psychosocial education.
However in New Zealand the current guidelines focus primarily on medication with little acknowledgement to the nutritional aspects of ADHD.
Research shows that certain foods, colourings, additives and preservatives can cause and exacerbate ADHD symptoms
Many parents have found that nutritional changes do decrease the symptoms of ADHD. There is considerable research to show that certain foods, colourings, additives and preservatives can cause and exacerbate ADHD symptoms[1-7]
It can be difficult to work out exactly what substances aggravate your child as children are likely to have different reactions to foods. The easiest way to start to help your child is to switch to a simple diet using fresh foods and avoiding all processed foods and drinks as these have been shown to affect ADHD behaviour 5] 
Avoid packaged food with a list of ingredients that sound nothing like the food in the package. Artificial food colouring and benzoates have been found to be especially detrimental for children with ADHD5] 
Studies suggest that certain foods may affect the electrical activity in the brain of children with ADHD
The toxic metal Mercury has been shown to affect the behaviour of children with ADHD. High fructose corn syrup which is often in proceed food can contain mercury. There can be other environmental sources of mercury. One of the many problems with mercury toxicity is that is can deplete Zinc.. , low levels of zinchave ben found in childrensuffereinf from ADHD. (NSDB,)[4, 8]
Nutrients that have ben shown to help children with ADHD
Other nutrients that have ben shown to help children with ADHD.Magnesium[4, 9, 10], which is found in whole grains, vegetables and nuts. Iron[4, 11, 12] found in meat(preferably organic), nuts, dark green vegetables and apricots. Selenium,  is low in New Zealand soils but can found in Garlic, Onions, Broccoli, Whole grains ,and oily fish.
Problems in absorbing the high quality fats
Children with ADHD can have a problem in absorbing the fats they need particularly the Omega3 Fatty acids[4, 13-15], EPA  DHA Omega3 Fatty acids[4, 13-15], so include fish in the diet.
Reactions to some foods
It may be that your child is reacting to a food that is, for other people completely harmless. To identify such foods an elimination diet can be used under supervision of a naturopath; studies have shown elimination diets to be an effective way of improving ADHD symptoms. 
1. Boris, M. and F.S. Mandel, Foods and additives are common causes of the attention deficit hyperactive disorder in children. Annals of Allergy, 1994. 72(5): p. 462.
2. Uhlig, T., et al., Topographic mapping of brain electrical activity in children with food-induced attention deficit hyperkinetic disorder. European journal of pediatrics, 1997. 156(7): p. 557-561.
3. Pelsser, L.M.J., et al., A randomised controlled trial into the effects of food on ADHD. European Child & Adolescent Psychiatry, 2009. 18(1): p. 12-19.
4. Sinn, N., Nutritional and dietary influences on attention deficit hyperactivity disorder. Nutrition Reviews, 2008. 66: p. 558-568.
5. Bateman, B., et al., The effects of a double blind, placebo controlled, artificial food colourings and benzoate preservative challenge on hyperactivity in a general population sample of preschool children. Archives of Disease in Childhood, 2004. 89(6): p. 506-511.
6. McCann, D., et al., Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial. The Lancet, 2007. 370(9598): p. 1560-1567.
7. Dufault, R., et al., Mercury exposure, nutritional deficiencies and metabolic disruptions may affect learning in children. Behavioral and Brain Functions, 2009. 5(1): p. 44.
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10. Kozielec, T. and B. Starobrat-Hermelin, Assessment of magnesium levels in children with attention deficit hyperactivity disorder (ADHD). Magnesium research: official organ of the International Society for the Development of Research on Magnesium, 1997. 10(2): p. 143.
11. Golub, M.S., C.E. Hogrefe, and S.L. Germann, Iron Deprivation during Fetal Development Changes the Behavior of Juvenile Rhesus Monkeys. J. Nutr., 2007. 137(4): p. 979-984.
12. Beard, J., Recent Evidence from Human and Animal Studies Regarding Iron Status and Infant Development . J. Nutr., 2007. 137(2): p. 524S-530.
13. Ramakrishnan, U., B. Imhoff-Kunsch, and A. DiGirolamo, Role of docosahexaenoic acid in maternal and child mental health. Am J Clin Nutr, 2009: p. ajcn.2008.26692F.
14. Lavialle, M., et al., An (n-3) Polyunsaturated Fatty Acid-Deficient Diet Disturbs Daily Locomotor Activity, Melatonin Rhythm, and Striatal Dopamine in Syrian Hamsters. J. Nutr., 2008. 138(9): p. 1719-1724.
15. Vaisman, N., et al., Correlation between changes in blood fatty acid composition and visual sustained attention performance in children with inattention: effect of dietary n-3 fatty acids containing phospholipids. Am J Clin Nutr, 2008. 87(5): p. 1170-1180.