For years, clinicians have suspected that diet may affect ADHD symptoms, and in recent years, research has suggested a potential impact of various aspects of diet on ADHD. This research includes examining the use of elimination diets, as well as studying the effects of omega-3 fatty acids and micronutrients on the disorder. Our knowledge in this area has begun to coalesce, and new directions have been illuminated.
Elimination and restriction diets
One of the most heavily speculated about and long-studied research areas in ADHD and nutrition is the use of elimination diets. While they come in many forms, in general, elimination diets are used to test whether the removal of specific dietary components leads to improvement in ADHD symptoms. In a second phase, elimination diets can be followed by dietary challenges, in which the food items being tested are given to patients, to observe whether symptoms return on reintroduction.
Mechanisms may reflect food allergies (immune-mediated reactions) and/or food sensitivities (nonimmunological reactions), but to date no laboratory tests have succeeded in predicting dietary response in youth with ADHD. Nonetheless, evidence of the past few years has consistently shown that restriction/elimination diets may be effective in reducing the ADHD symptoms, with up to a 30% probability of response.1 This effect size likely masks wide variation in response, with some children responding more beneficially than others.
Artificial food coloring and preservatives have been the primary foci of food sensitivity in children with ADHD. A recent meta-analysis concluded that there is enough evidence to suggest that artificial coloring can be a trigger for some patients, with a modest effect of g = 0.29, although with a fairly wide confidence interval because of the small size of the studies that have been reported.2 Thus, it may be that for some youths, a diet free of processed foods containing additives, particularly colorings and preservatives, would improve symptoms. Processed foods are major sources of artificial colors, especially in children’s foods and drinks, in which bright colors are used to make food more attractive.
There has been great interest in the potential for polyunsaturated fatty acids and, in particular, omega-3 fatty acids to modify ADHD symptoms. The literature includes nearly 2 dozen studies involving hundreds of children. Meta-analyses have now demonstrated that low circulating concentrations of omega-3 fatty acids are associated with ADHD, and that omega-3 fatty acid supplementation has a similarly small but reliable benefit as the restriction of food additives.3-5 The effect size for both the restriction of artificial colors and supplementation with omega-3 fatty acids is about one-quarter the size of a medication effect.
Although recent literature reviews have concluded that omega-3 fatty acid supplementation is an effective treatment (category 5) and dietary restriction is a probably effective (category 4) intervention, no dietary changes are currently recognized in formal clinical guidelines for ADHD treatment. Thus, these remain options for complementary or alternative treatments.
It may be that food restriction—as well as supplementation with omega-3 fatty acids—produces only modest aggregate effects due to substantial variation in response, with some children having greater benefits than others. However, another possibility is that larger effects would accrue when these dietary strategies are combined with adequate micronutrient intake. For example, other nutrients (eg, vitamin D, minerals), in combination with omega-3 fatty acids, may provide synergistic effects over omega-3 fatty acids alone.
Dr. Holton is Assistant Professor, Department of Health Studies, Center for Behavioral Neuroscience, American University, Washington, DC. Dr. Johnstone is a Postdoctoral Fellow in Neurology and a Psychology Resident, Department of Child and Adolescent Psychiatry; Dr. Stadler is Associate Professor of Medicine and Director of the Graduate Programs in Human Nutrition; Dr. Nigg is Professor, Department of Psychiatry, Pediatrics, and Behavioral Neuroscience, Oregon Health and Science University, Portland, OR. The authors report no conflicts of interest concerning the subject matter of this article. Dr. Johnstone receives funding from NIH-NCCIM T32 AT002688.
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