Fixing nutrient deficiencies can also have positive effects for kids with autism. Because of their inability to properly digest food and absorb nutrients, many children with these disorders may be low in zinc, magnesium, B vitamins, iron, essential fatty acids, and other nutrients. Lack of magnesium, for instance, can cause hyperactive-like behavior, sound sensitivity, and irritability. Zinc deficiency a result of a defect in zinc metabolism that's common in autistic children and can be exacerbated by diets high in white flour and other high-hypoglycemic foods — can change a child's sense of taste and smell.