In the present study, we observed that more than half of studied children were stunted. Mentally retarded children were more affected compared with other children. Compared with children in the lowest category of dairy consumption, those in the highest category had lower odds of stunting. This association remained significant even after adjusting for covariates. In addition, moderate consumption of egg (1–3 time/wk) was inversely associated with stunting either before or after controlling for potential confounders. Such finding was also seen among mentally retarded children. No other significant association was seen between intakes of other food groups and stunting. Therefore, we conducted this first study to assess the association between intakes of food groups and stunting in exceptional children.
Stunting is related to high morbidity during childhood and it’s consequence in adulthood . This condition can increase risk of overweight, obesity and related diseases such as metabolic syndrome in adulthood [17, 18]. Furthermore, stunting in children can affect the cognitive status and also reduce work capacity [5, 19]. Nutritional deficiency has an important role in etiology of stunting. A large number of studies have assessed the association between dietary intakes and stunting [5, 20, 21]. Also, the nutritional status of exceptional children has received less attention such as mentally retarded ones. Our findings indicated that a significant inverse association between dairy consumption and stunting. A prospective cohort study by Nguyen et al. were showed that consumption of dairy products was decreased risk of stunting . In another cohort study, children who consumed higher amount of milk had better height growth, while consumption of other dairy products revealed no beneficial effect on linear growth . However, the mentioned studies were conducted on healthy children, not exceptional ones. To our knowledge, we found no study assessing the association between dairy consumption and stunting in exceptional children.
Dairy products contain protein and calcium, which can explain the value of dairy products on linear growth in children [24, 25]. Evidence suggests adequate calcium intake is involved in bone mineralization and linear growth [26, 27]. Therefore, appropriate intake of calcium may decrease stunting phenomenon. Furthermore, dairy products are a rich source of high-biological value proteins that are required for linear growth [26, 28]. Consumption of these proteins stimulates the secretion insulin-like growth factor 1, known as contributing factor in linear growth of bone and mineralization . On the other hand, children need more calcium and high-quality proteins (relative to weight) compared with adults because of rapid linear growth [30, 31]. Therefore, children who eat more dairy products, have higher bone and linear growth.
In current study, we also observed that moderate intake of egg was decreased risk of stunting among exceptional children and also those who were mentally retarded. Some studies had shown similar findings in healthy children. Results from a clinical trial showed that children who consumed 10 eggs per week during 6 months had better linear growth compared with those who ate ≤ 1 egg per week . Similarly, Lee et al. reported  that consumption of egg in short stature children were significantly lower than those with normal height. In contrast, in a cross-sectional study on children in Ethiopia, Melaku et al. showed that higher adherence to a dietary pattern rich in egg was increased risk of stunting . Perhaps this inconsistency in Melaku et al.  study was due to the evaluation of the egg-rich dietary pattern, not intake of egg alone, compared with present and previous studies. In addition, existence of contraversion findings can also be explained by the impact of different cooking methods in different communities.
In this study, we did not observe any association between the third tertile of egg consumption and stunting, which seems to be due to the small number of participants in this tertile and the widening of the confidence interval. Another reason might be cholesterol content of egg. Recently, stunted children were showed with high level of cholesterol compared to normal-height ones. Therefore, high intake of egg may stimulate stunting through elevation of total cholesterol concentrations.
Egg also, contains high- biological value proteins that are required for skeletal and linear growth. In addition, egg is known as a rich source of choline and essential fatty acids. Choline as a precursor of phospholipids is important for growth and development . Some studies have confirmed that choline have beneficial effects on linear growth [35, 36]. In a study by Semba et al.  on rural Malawi children, stunted children had lower serum choline levels than those with normal height children . In addition, cell proliferation that is the first step of linear growth needs proteins, choline and essential fatty acids that are available in egg [32, 35, 37]. Since in some communities these children are kept in day care institutions, there are restrictions on their food choices. Swallowing milk and eggs is easy and many children are interested in eating them. Therefore, the inclusion of milk and eggs, especially in snacks, can play an important role in the development of these children.
In the current study, we did not any association between other food groups intake including meat, fruits and vegetables and risk of stunting. This association remained non-significant even after adjustment for potential confounders. However, most previous studies showed an inverse association. For example, Lee et al.  observed that consumption of meat, fruits and vegetables in normal height children were higher than stunted children . These food groups are rich in antioxidants, different types of vitamins and minerals and also proteins which all are necessary for growth and development . Different physical condition of children participated in the current study compared with those who participated in the earlier studies might be a reason for the lack of significant association between these food groups (meat, fruits and vegetables) and stunting in the current study. Chewing meat, fruits and vegetables for exceptional children particularly those who were mentally retarded might be more difficult than healthy children. In addition, energy intake of exceptional children might be low due to their physical condition and it is possible that beneficial effects of meat, fruits and vegetables intakes on height might occur in the range of required energy intake. However, we did not measure energy intake in the current study. It is suggested that future studies consider this important variable for diet-disease relationships in exceptional children.
Unfortunately, this study suffered from some limitations which made our findings inconsistent. Based on the cross-sectional design of our study, we cannot confer a causal link between intakes of food groups and stunting. First, since the study design is cross-sectional, the cause-and-effect relationship between food groups and short stature is not clear. Therefore, these findings should be supported by prospective studies. Second, given that the use of questionnaires to collect nutritional data is a common method in studies, remembering the foods consumed can cause errors. However, this information was requested and recorded by an experienced and trained nutritionist. Although we adjusted some confounders for to assess the association between food groups intake and stunting, it seems that some other variables such as energy intake, parents’ height, economic status and physical activity need to be considered in future studies in which we did not collect data on these variables in the present study.