Dietary modifications are not recommended as of 2019 by the American Academy of Pediatrics, the National Institute for Health and Care Excellence, or the Agency for Healthcare Research and Quality due to insufficient evidence. A 2013 meta-analysis found less than a third of children with ADHD see some improvement in symptoms with free fatty acid supplementation or decreased eating of artificial food colouring. These benefits may be limited to children with food sensitivities or those who are simultaneously being treated with ADHD medications. This review also found that evidence does not support removing other foods from the diet to treat ADHD. A 2014 review found that an elimination diet results in a small overall benefit in a minority of children, such as those with allergies. A 2016 review stated that the use of a gluten-free diet as standard ADHD treatment is not advised. A 2017 review showed that a few-foods elimination diet may help children too young to be medicated or not responding to medication, while free fatty acid supplementation or decreased eating of artificial food colouring as standard ADHD treatment is not advised. Chronic deficiencies of iron, magnesium and iodine may have a negative impact on ADHD symptoms. There is a small amount of evidence that lower tissue zinc levels may be associated with ADHD. In the absence of a demonstrated zinc deficiency (which is rare outside of developing countries), zinc supplementation is not recommended as treatment for ADHD. However, zinc supplementation may reduce the minimum effective dose of amphetamine when it is used with amphetamine for the treatment of ADHD.