Atopic dermatitis (AD), a chronic relapsing inflammatory skin disease commonly associated with allergy, affects 15% to 30% of children [1]. Many children who develop AD go on to develop other allergic diseases, such as food allergy (FA), asthma, or allergic rhinitis (the 'atopic march') [2]. FA is an adverse health effect arising from a specific immune response that occurs reproducibly upon exposure to a given food [3]. The clinical spectrum of FA ranges from mild skin irritation to severe life-threatening anaphylaxis [4].

The majority of FAs are mediated by immunoglobulin E (IgE), however, sensitization to a specific food as confirmed by skin prick test (SPT) or serum-specific IgE does not always imply clinical reactivity. Accurate diagnosis of FAs should be based on an oral food challenge [5-7]. The delayed onset of symptoms in FA (6 hours to as long as 48 hours after the food challenge) makes observation difficult, although as many as 25% of cases will present within 1-2 hours of ingestion [8]. There are no specific laboratory tests for FAs; therefore, diagnoses are made using elimination diets and oral challenges [9,10] as well as food challenge tests [11,12]. Several food challenge methods have been proposed, including double-blind placebo-controlled food challenges (DBPCFC) and open food challenges (OFC) [3]. In an OFC, the patient is not blinded and therefore recognizes the test food. Test results are then interpreted according to objective symptoms. If the patient shows anxiety regarding the challenge and complains of abdominal pain or pruritus, the food challenge test is considered invalid [3]. DBPCFC is regarded as a more accurate method for diagnosis of FAs, because both the patient and the observer are blinded to the test food. While this is the most rigorous method for diagnosis of adverse food reactions [13], conduct of DBPCFCs in the clinical setting is difficult.

The current standard of care for patients with food allergies is based on avoidance of trigger foods with the goal of eventually gaining tolerance [14]. In those with food allergies that are thought to cause aggravation of eczema, food avoidance is important. However, due to the risk of nutritional deficiencies, careful supervision of such diets is also vital, particularly if calcium-rich foods are avoided [15]. In many cases, multiple foods are the cause of AD, and food allergies are not the only cause of AD. More than 50% of FA patients also have food allergies to more than one food, with the average FA patient experiencing symptoms from 2.8 food items [16].

Care should be taken to ensure that diet is nutritionally adequate, especially for those with multiple allergies. Without elimination of allergy provocation, AD cannot be controlled effectively. As a first step toward the diagnosis of food allergy, dietary restrictions should be initiated. If a patient shows improvement in symptoms on an elimination diet, a food allergy to the restricted foods may be strongly suspected. An optimal elimination diet can then be achieved.

In Korea, the prevalence of food allergies by OFC testing among patients with AD were as follows: milk, 67.3%; chicken, 64.2%; pork, 62.8%; eggs, 61.0%; beef, 55.4%; wheat, 52.0%; and soybeans. 45.2%. Little research on these seven specific foods has been reported [17]. Unfortunately, these seven foods are also rich in important nutrients. During treatment of FA, prevention of excessive food elimination and proper use of alternatives are required. Various studies have highlighted cases of reported growth delay and nutrient deficiency in patients experiencing excessive food limitation [2,8,15]. However, few studies on food limitation in FA patients in countries including Korea have been reported [10,16].

Therefore, the aim of this study is to identify practically deficient nutrients by researching nutrient status of FA patients. We intend to provide basic information that can be used for establishment of appropriate health and dietary guidelines.

A food allergy can only be diagnosed with certainty by elimination-provocation tests [20]. Probable allergens are removed in order to create the elimination diet. If symptoms disappear during elimination, a food allergy is likely the cause of the symptoms. The cause can be established by reintroducing foods one at a time. Some subjects were positive for SPT and blood IgE tests, despite not showing allergic responses during food challenge tests (OFC and DBPCFC). No specific food was limited for consumption; however, most of the subjects did not consume the recommended amount of food and nutrients. For proteins, lipids, and carbohydrates, subjects under the age of 5 who were positive for FA consumed less than those who were negative for FA. The opposite was true for patients age 6 and older. At all ages, the subjects showed deficient Ca intake, and Ca intake was lower in FA-positive subjects in the group of patients who were 12 years old and younger-the ages of rapid growth. According to Chang et al. [21], parents of AD patients with chronic atopic disease, especially mothers, suffer from acute stress. They often use scientifically unproven therapy as a result of fears and worries. They also show extreme concern and tension. Such behaviors may cause limited selection of foods. Dietary factors, such as a low intake of antioxidants may affect the risk of AD and asthma [22,23]. Several studies conducted in AD and asthma patients reported that intake of several foods containing high levels of vitamin C and vitamin A was related to a decrease in the risk of these diseases [23-25]. Our results showed that AD subjects were lacking in several nutrients, including vitamin A and vitamin C. A greater number of food allergens showed an association with an increase in number of deficient nutrients.

Allergen avoidance is the treatment for AD. However, when the allergen is food, excessive restriction can lead to nutrition deficiency. Relevant to atopic diseases, the effects of nutrition on the manifestation and severity of atopic disorders were carefully reviewed in a previous study [26]. In this regard, two different approaches have been studied as preventive measures for various atopic diseases: (1) an elimination diet aimed at omission of causative nutrients and (2) a supplementary diet aimed at addition of protective nutrients [27].

We analyzed nutrient intake according to the kinds of food allergen in subjects with FA for seven food items. Subjects with milk allergy had lower intake of Ca, Zn, and vitamin B₂, and subjects with egg allergy had lower intake of vitamin A, vitamin B₁, vitamin B₂, niacin, and cholesterol. Subjects with FA to wheat and soybean had lower intake of Ca, P, Fe, K, Zn, vitamin B₂, vitamin B₆, and niacin. Subjects with FA to beef, pork, and chicken had lower intake of Fe and higher intake of Ca, K, vitamin A, B₂.

Because most causative agents of FAs are foods that provide valuable nutrients, consumption of replacement food containing similar nutrients should be emphasized in order to prevent malnutrition. Avoidance of symptom-causing foods should be in accordance with tolerance: thus, if food-induced symptoms are mild and occur only after ingestion of higher doses, there is no need for a strict elimination diet [20].

In this study, we investigated seven food items as causative foods for food allergy symptoms, the result of food limitation to AD patients, and associated nutrient intake. Findings of this study suggest the necessity for enhanced nutritional education for replacement foods in order to provide FA patients with information necessary for acquisition of adequate nutrition. Following this study, investigation of the impact of excessive food limitation on growth, malnutrition, and AD management is needed. Further studies should investigate systems and strategies for mitigation of harm from excessive limitation. Regarding the limitations of this study, the number of subjects in each age group is not large enough, even though FA patients were studied for 10 years, from 2000 to 2010. Despite a long period of time for collection or gathering of information in order to obtain accurate results from FA patients, the number of patients is insufficient. Therefore, in the future, this study is expected to continue.