The results of this study suggest that children with autism are at least as likely to be obese as children who do not have autism. Based on our analysis, our best estimate indicates that children with autism are 40% more likely to be obese compared with children without autism. However, because the number of children with autism assessed was small, estimates cannot be broken out by age and sex of the child, and the confidence interval for the overall prevalence of obesity in children with autism is wide. Thus, our estimate is consistent both with children with autism having the same prevalence of obesity as other children as well as children with autism being twice as likely to be obese as other children.
Although obesity is always a result of an energy imbalance, the specific factors that contribute to excess energy intake and/or low energy expenditure among various subgroups of the general population are not yet well understood. Our analyses of the National Survey of Children's Health are descriptive and not designed to explore risk factors for obesity in children with autism. For this reason we did not adjust the estimates presented for sociodemographic or other covariates. Children with ASDs may have atypical physical activity and eating patterns that are uniquely associated with the development of obesity. For example, children with ASDs are known to have motor impairments that may adversely affect their ability to participate in sports or physical activities successfully. Such motor impairments include poor motor skills, unevenness of developmental milestone acquisition, low muscle-tone, oral-motor problems, and postural instability[16–23]. In addition, children with ASDs may experience low levels of physical activity due to their impairments in social skills which may limit participation in structured activities with peers. In fact, a recent study found that praxis/motor planning in children with autism was strongly correlated with the social, communicative, and behavioral impairments that define the disorder.
Children with ASDs have also been reported to have unusual eating habits, most frequently described as overly selective. A handful of small studies have documented that children with ASDs have aversions to specific textures, colors, smells, temperatures, and brand names of foods, with some preferences for soft and sweet foods [25–28]. In a larger study, Schreck et al.  reported that children with autism demonstrated more food selectivity than typically developing children and that the children with autism preferred energy dense foods within food groups (e.g., chicken nuggets, hotdogs, peanut butter, cake, etc.). It is possible that these eating patterns may contribute to the development of obesity in this population of children.
A strength of this study is that it is based on nationally representative data and adds to the extant literature that is primarily comprised of smaller studies. However, several limitations of the current study are noteworthy. The key measures are provided by parental report as part of a telephone interview rather than direct measurement or observation. For example, height and weight were reported by parents and not independently measured. The validity of parental report of children's height and weight has recently been shown to be at variance with direct measures, particularly in young children. A recent examination of the parent-reported height and weight for children in the current NSCH data set as well as data from the 1999-2004 National Health Interview Survey (NHIS) were compared to direct measures taken in the 1999-2004 National Health and Nutrition Examination Survey (NHANES), a nationally representative survey When compared to measured data obtained from NHANES, the parent-reported data in the NSCH and NHIS over-estimated overweight among younger children and under-estimated overweight among older children. This was attributed to discrepancies in reported height among very young children. The authors conclude that these findings support previous recommendations that parent-reported data should not be used to estimate overweight prevalence among preschool and elementary school-aged children. Thus, further study of children with autism that includes measured height and weight is warranted to confirm the findings we present. Other limitations include that autism was established by an affirmative answer to a single question about whether a doctor or health professional had ever told the parent the child had autism.