Worldwide, 5–10% of all children and 4% of all adults are affected by attention-deficit/hyperactivity disorder (ADHD) [1,2,3,4,5]. Psychostimulants are the first choice medication for treating ADHD in children, adolescents, and adults [6]. Drug treatment has been used for over 50 years and leads to symptom reduction in about 70% of all patients [7,8]. In some cases, medication can lead to negative side effects, such as sleep disturbances, loss of appetite, stomach complaints, nausea, and vomiting. Many factors play a role in the pathophysiology and treatment of ADHD: genetics, neurology [9], and psychology [10], but also food intolerances [5,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. Already 100 years ago, Shannon [10] observed increased restlessness and sleep disturbances in children with food intolerances. In 1961, the food intolerance hypothesis was supported by Crook et al. [33]. They determined that behavioral disorders can be caused by the ingestion of milk, cereals, eggs, or chocolate. It is known that children with ADHD differ in oligosaccharide metabolism [34], show more lactose intolerance [35], and have a higher incidence of celiac disease [36] as compared to healthy children. The role of the gut microbiome has been discussed [37,38]. In the early 1980s, Egger et al. proposed that food could trigger behavior problems [28]. Therefore, they used an oligoantigenic diet (OD) in children with the hyperkinetic syndrome. The OD is a diet that avoids certain foods that often trigger allergies or intolerances. Consequently, during the diet, participants eat foods that are proven to be hypoallergenic. The diet we used followed the food choices of Egger et al. [39] and Carter et al. [40], consisting typically of two types of meat (e.g., lamb and chicken), two carbohydrate sources (e.g., potatoes and rice), two fruits (e.g., banana and apple), vegetable (e.g., any brassica), calcium-rich water, and vitamin supplementation. The diet was adjusted to suit the tastes and habits of the family and to avoid any foods suspected of causing symptoms and those for which the child had a particular craving or dislike.In our open uncontrolled study, Yorgidis et al. could replicate and confirm previous results of the efficacy of the OD on children with ADHD in a pre-post design [42,43]. The participants showed individual food sensitivity concerning the type of food, intensity, or pattern of reactivity. In all patients, ADHD symptoms were intensified by various foods during the food challenge after OD. Because every participant reacted very individually to different foods, there must be an individual dietary recommendation for each individual child. Stevenson et al. [13] pointed out in their research review from 2014 that a restricted elimination diet might be beneficial for ADHD symptoms in children and adults. Subsequently, detected individual food sensitivities leading to individualized dietary recommendations are useful as an additional option to the existing multimodal therapy concept.