Using nationally representative data this present study aimed to assess the association between measured parent weight status, familial SES factors and the risk of childhood obesity. This research has resulted in two principal findings. Firstly, parent weight status appears to be the most significant independent predictor of childhood obesity in Ireland. Children from families with overweight or obese parents were at a significantly higher risk of obesity than children with normal weight parents. Secondly, household class and maternal education are better predictors of childhood obesity than household income.
Only 18.9% of children were from families (either single parent or two parent families) with normal weight parents. Having normal weight parents appears to have a protective effect against the risk of childhood obesity. Only 14.4% of children from such families were overweight or obese whereas 46.2% of children with obese parents were overweight or obese. After adjustment for household socio-economic characteristics, children from obese parent families remained at greater than 15 (95% CI, 8.44–27.65) times the odds of obesity when compared to children from families with normal weight parents. This suggests that SES alone cannot explain the association between parent obesity and child obesity. SES indicators appear to only capture some shared familial environmental factors which result in weight gain. We suggest that these results highlight that the shared family environment is a multi-dimensional contributor to the obesity epidemic with both genetic and environmental origins.
Within this present study, children who were more deprived were at a higher risk of overweight and obesity, which is similar to results found in adults 
. Children from one parent families were found to be at significantly higher odds of overweight and obesity than children from two parent families. Some research suggests that one parent families may have greater levels of social deprivation and this may play a role in explaining this 
. However, our results indicate that parental weight was more predictive overweight and obesity in children from single parent families than SES. There was an inverse association between household class and maternal education with childhood obesity. The association between household class and childhood obesity was more graded. Within the final adjusted model, children from a lower household class were at higher odds of obesity than children with lesser educated mothers. Research indicates that parental education is the SES indicator most consistently associated with childhood obesity 
. This may be because maternal education is a more stable indicator of SES over time than household income or household class. Maternal education is likely to influence factors including literacy as well as knowledge of healthy versus unhealthy behaviours which impact on weight status 
. As a higher level of education appears protective against child obesity, this suggests that education may be crucial in tackling the obesity epidemic. Overall, variations in odds of obesity by each indicator of SES suggest that household class, household income and maternal education may all influence different behaviours and choices that impact weight gain. Further research is required to fully understand how each SES characteristic predicts behaviours which result in weight gain. In addition, efforts are necessary to standardise SES indicators and definitions used across studies.
In this study SES indicators do not explain all the association between parent and child weight. Therefore, other causal pathways for childhood obesity need to be considered. Research from other studies of childhood obesity indicate that the weight status of parents from 2 parent families may interact 
. Mechanisms resulting in a positive energy balance in both parents appear to be more predictive of childhood obesity than such mechanisms in one parent. In this current research having 2 obese parents compared with one obese parent resulted in a 2 fold increase in the odds of childhood obesity.
A study by Wardle et al. 
compared food, physical activity and lifestyle patterns in children from lean and obese families. This study found that children from obese families had higher preferences for fatty foods and sedentary activities and a lower preference for fruit and vegetable consumption. Such food and physical activity patterns may have a negative impact on energy balance resulting in weight gain. Such diet and activity patterns may potentially explain the lack of significance for household income in this present study. Parent weight status may be a better predictor of food types purchased rather than income or other measures of household SES. More affluent families with obese parents may have a preference for energy dense food regardless of income available to spend on good quality foods. Grunert at al. 
suggest that habitual behaviour is difficult to change even if an individual is aware of the negative consequences of their behaviours. Grunert et al. suggest that obese individuals have a greater response to external cues (sight, smell) for food intake whilst normal weight individuals respond to internal cues (hungry). Children may acquire habitual behaviours and responses to dietary and physical activity patterns from that of their parents. Another possible explanation is that genotypes including the FTO gene which impacts appetite may influence control over food intake and choices resulting in children from obese families having a greater predisposition for obesity 
Similar to other findings 
, maternal obesity was more predictive of a child being in a higher BMI category than paternal obesity. There are a number of possible explanations for this. Mothers were nominated as the primary caregiver (the person who spent most time with the study child) for 98% of children who took part in this study. This indicates that children spend more time in their mother’s environment and thus may acquire more behaviour’s from their mother. A study by Hannon et al. 
found that the eating habits of the family food preparer, 84% of whom were mothers, predicted the eating habits of their child. Birth factors including the role of the intra-uterine environment on subsequent risk of childhood obesity is a second possible explanation 
Strengths and Limitations
GUI is a large and nationally representative sample. The sample equates to approximately one in seven of all births in Ireland in 1997. The results of the study are applicable at a population level as a result of applying the sampling weights. All objective BMI measurements were measured by trained professionals using validated techniques. The study contains information on three indicators of SES (household class, equivalised household income and maternal highest level of education). Imputing the household income variable decreased the amount of missing data.
However, there are several limitations to the study. There was a relatively low response rate at the household level (57%). The data have been weighed to adjust for the sampling strategy and response rate. However, there may be residual response bias. Of the children with measured BMI, there was missing values for BMI for 2% of mothers and 6.9% of fathers. Data was also missing for income for 7.3% of the households. While the missing data imputation procedure has enhanced the study power, it would have been preferable not to have missing data on this key variable. The data analysed in this present research is cross-sectional. Therefore, a causal relationship cannot be inferred though as the children are only 9 years old it is likely that parental and SES factors partly predicted the onset of obesity.
Parent weight status is a significant predictor of childhood obesity. Children from lower household class families and those with lesser educated mothers were at an increased risk of childhood obesity. Early intervention is required to tackle the problem of childhood obesity. It may be suggested to target interventions at families where parents are overweight or obese. However, we must consider that in the current study, this includes the majority (81%) of families. Thus, the findings highlight the need for broadly based population level interventions targeting the social, economic and cultural dimensions of overweight and obesity. Further research is needed to assess how behaviours that affect energy balance vary between families with normal weight parents versus families with obese parents.