Design

This research involved data from the Childhood Growth and Development (GAD) Study. The GAD Study is a prospective cohort study based in Perth, Western Australia, which has a central focus on weight and eating behaviour in childhood. Children were recruited from Perth primary schools and interviewed at baseline (Time 1), 1-year follow-up (Time 2), and 2-year follow-up (Time 3). Additional details of the GAD Study methodology, including detailed recruitment information, have been reported previously[38–40].

Participants

Participants were community-recruited mother-child dyads where the child was aged between 8 and 13 years at baseline and where baseline, 1-year follow-up and 2-year follow-up assessments were completed between January 2004 and January 2009. This equated to 221 children (46% male) and, due to 55 sibling pairs or triplets, 166 mothers. Family clustering was accounted for in analyses. There were 15 father-child dyads who were excluded from analyses, due to the small number of participating fathers and the focus on maternal characteristics in analyses.

Participant attrition over the 2-year period was 32% (baseline N = 325 children). Differences between families included in this study and those lost to follow-up are discussed under Preliminary Analyses, below.

At the baseline assessment, children had a mean age of 10.78 years (SD 1.72, range = 8-13 years) and mothers had a mean age of 40.98 years (SD 5.17, range = 30-54 years). As the mean age of the sample exceeded 12 years at Time 3, pubertal stage was considered as a possible confounder of the results. This was assessed via self-report Tanner stages[41], which have been found to converge well with physical examination in pre-adolescent samples[42, 43]. All boys were pre-pubertal at baseline and 93% (n = 95/102) remained pre-pubertal at 2-year follow-up. There were no significant differences between pre- and post-pubertal boys at 2-year follow-up, for any of the assessed variables. Most girls (94%; n = 112/119) were pre-pubertal at baseline and 72% (n = 86/119) were pre-pubertal at 2-year follow-up. Girls who were post-pubertal were significantly older than girls who were not at both time points, but pubertal status did not relate significantly to the family variables of interest or children’s eating disorder symptoms. Thus, pubertal status was not included as a covariate in analyses.

Procedure

Children and mothers were assessed separately by trained GAD Study researchers, at baseline, 1-year follow-up, and 2-year follow-up. Assessments were conducted in the family’s own home, at the Telethon Institute for Child Health Research or at Princess Margaret Hospital for Children, according to family preference. With the exception of the GAD Study interview questions and the Eating Disorder Examination (EDE;[44]), all maternal measures were completed as self-report questionnaires. In contrast, all child measures were administered verbally. The same measures were administered at all assessment points.

All GAD Study researchers received comprehensive training prior to conducting assessments, and had Honours level qualifications or above in psychology, medicine or exercise physiology. Training for the EDE and ChEDE was conducted by the first and last authors, who have extensive experience with the administration of these interviews. The first author also checked all EDE/ChEDE scores prior to data entry, to ensure adherence to scoring protocols.

Ethics approval was provided by the Ethics Committee of Princess Margaret Hospital for Children. Mothers provided written informed consent for participation.

Outcome variables: child feeding problems and eating disorder symptoms

Child feeding problems (maternal report)

Questions about early feeding practices were included in the GAD Study parent interview. Specifically, two questions were used to determine the age at which mothers stopped breastfeeding their child(ren) (to the nearest week; 0 weeks if they did not breastfeed at all) and the age at which they started their child(ren) on solid food (to the nearest month).

Child eating disorder symptoms (child report)

Child eating disorder symptoms were assessed using the Child Eating Disorder Examination (ChEDE)[45] and Children’s Affect Regulation Scale (CARES)[46].

The ChEDE is a semi-structured interview adapted from the adult Eating Disorder Examination (EDE)[44]. Like the adult version, it generates four subscale scores (Restraint, Eating Concern, Weight Concern, Shape Concern) and a Global score (the mean of the four subscale scores). A Brief Global score appears to be a more reliable index of eating pathology than the original four subscales, which are not supported by factor analysis[47, 48]. The brief scale consists of eight items from the original Weight Concern and Shape Concern scales, and the resulting index correlates very highly with the original Global score and moderately to highly with each of the original four subscales[47, 48]. This study used the Brief Global score as an index of overall child eating disorder psychopathology (α = .88 at baseline). To allow a specific focus on dietary restraint, we also made use of the ChEDE Restraint scale, which consists of 5 items regarding actual and intended dieting behaviour (α at baseline = .69).

The ChEDE also allows children to be categorised according to whether or not they experienced loss of control or ‘binge’ eating. Loss of control eating encompasses objective binge eating (feeling out of control of one’s eating and consuming an objectively large amount of food) and subjective binge eating (feeling out of control of one’s eating but not consuming a large amount of food). It is established that loss of control, regardless of the amount of food eaten, is the key component of binge eating behaviour in childhood[49] and objective and subjective binge eating were both considered for this research.

The CARES was used to assess emotional eating. The measure includes 10 items that assess the tendency to eat as a means of affect regulation. Scores can range from 0 (no emotional eating) to 4 (very frequent emotional eating). The alpha coefficient was .82 at baseline.

Predictor variables: family characteristics

Maternal eating disorder and psychiatric disorder history (maternal report)

Five questions in the GAD Study parent interview were used to determine if mothers (i) had ever had an eating disorder or been suspected of having one and, if yes, (ii) the nature of the disorder, (iii) when it occurred, (iv) if it was diagnosed, and (v) if it was treated.

Five additional questions in the GAD Study parent interview were used to determine if mothers (i) had ever experienced an emotional or psychological problem not related to eating and, if yes, (ii) the nature of the problem/s, (iii) when they occurred, (iv) if they were diagnosed, and (v) if they were treated.

Responses to these items were used to categorise mothers according to whether they had a past eating disorder history, a non-eating related current or past psychiatric disorder, or no history of a psychiatric disorder.

Current maternal eating disorder symptoms (maternal report)

The adult EDE version 12 was used to assess current maternal eating disorder symptoms. As per the ChEDE, this semi-structured interview generates four subscale scores (Restraint, Eating Concern, Weight Concern, Shape Concern) and a Global score (the mean of the four subscale scores), and includes diagnostic items for determining eating disorder diagnoses. The measure is established as reliable and valid[50–53]. Again, there is greater support for the Brief Global scale than the original subscales[47]. This study used the Brief Global score as an index of overall maternal eating disorder psychopathology (α = .85 at baseline). Diagnostic items were used to determine current DSM-5 eating disorder diagnoses in mothers.

Maternal concern about child weight (maternal report)

One question in the GAD Study parent interview was used to assess mother’s level of concern about their child(ren)’s weight, with the available response options being “not at all”, “a little”, “moderately” or “very” concerned. If the mother had multiple children participating in the study, separate ratings were made for each. As very few mothers reported being “very” concerned, responses in the two highest categories were collapsed to give a moderate-high concern group.

An additional question was used to assess mother’s level of concern about their child(ren)’s overall health. Mothers rated their child(ren)’s current physical health on a 5-point scale ranging from “poor” (1) to “excellent” (5).

Family relationships (maternal and child report)

Family relationships were assessed in two ways. First, mothers completed the self-report General Functioning Scale (GFS) of the McMaster Family Functioning Device[54]. The GFS includes 12 items regarding family relationships, arguments and interactions, and has been established as reliable and valid with a variety of clinical and non-clinical groups[54–57]. Higher scores indicate greater family conflict and disharmony. The alpha coefficient in this sample was .90 at baseline.

Second, the Family Satisfaction subscale of the Students’ Life Satisfaction Scale (SLSS;[58]) was verbally administered to children. This subscale is designed to assess children’s level of satisfaction with their family, parents, and the nature of family interactions. It contains seven items, and subscale scores can range from 0 to 5; higher scores indicate greater family satisfaction. The measure has been established as reliable and valid[58–60], and the alpha coefficient in this sample was .78 at baseline.

Parenting style (maternal report)

The Parenting Scale[61] was used to assess for unhelpful parenting practices. The scale includes 30 items regarding overly permissive discipline (“Laxness”), inappropriate displays of anger, meanness or irritability (“Overreactivity”), and the use of lengthy verbal responses or instructions even when ineffective (“Verbosity”). It can be used to generate subscale scores for each of these categories of items, as well as an overall global score. In each instance, scores can range from one to seven, with higher scores indicating less positive parenting. The measure has acceptable psychometric properties, although the factor structure of the three subscales has been debated[62, 63]. Global scores were used in this study and the 30 items were internally consistent (α = .78).

Family exposure to stressful life events (maternal report)

The List of Threatening Experiences[64], otherwise known as the Life Events Scale, was used to assess family exposure to stressful life events. The scale asks respondents to indicate if they have experienced each of 12 negative life events (e.g., unemployment, significant illness) over the past 6 months, with scores calculated by summing the number of “yes” responses. It has been established as a valid index of life stress[65–67].

Maternal depressive, anxiety and stress symptoms (maternal report)

The 21-item self-report Depression Anxiety Stress Scale (DASS)[68] was used to assess maternal depressive, anxiety and stress symptoms experienced over the previous week. The DASS generates three subscale scores (Depression, Anxiety and Stress) that can range from 0 to 42. It has been established as reliable and valid[68–72]. Scores on the Depression subscale correlate highly with scores on other measures of depression, and scores on the Anxiety subscale correlate highly with those on other measures of anxiety[68, 69, 71]. Alpha coefficients were satisfactory in this sample (=.77 - .86).

Maternal self-esteem (maternal report)

The Rosenberg Self-Esteem Scale (RSES)[73] was used to assess overall maternal self-esteem. The scale includes 10 items and scores can range from 10 to 40, with higher scores indicating greater self-esteem. It has well-established psychometric properties[73–75]. The alpha coefficient at baseline was .88.

Covariates and additional descriptive variables

Child psychosocial functioning (child report)

Indices of child psychosocial functioning were considered as potential confounders of associations between family characteristics and child eating disorder symptoms.

The short form of the Child Depression Inventory (CDI)[76] was used to assess depressive symptoms. The CDI is a modification of the Beck Depression Inventory, and is the most commonly used instrument for assessing depressive symptoms in children. The short-form CDI contains 10 items that assess negative mood, anhedonia, ineffectiveness, and negative self-esteem, and it has been established as internally consistent and successfully used to screen children for depression[76]. It was internally consistent in this sample (α = .73 at baseline).

The Global Self-Worth subscale of the Self-Perception Profile for Children (SPPC)[77] was used to assess children’s overall or global level of self-esteem. The SPPC is a multi-dimensional measure of self-esteem and has been validated for use with participants aged eight years and older[77, 78]. The alpha coefficient for the Global Self-Worth scale at baseline was .71.

The Multidimensional Media Influences Scale (MMIS)[79] was used to assess children’s awareness and internalisation of the thin-ideal, and their perceived level of media pressure to achieve the thin ideal. It has acceptable psychometric properties[79] and the total score was used in this study (α = .75).

Family sociodemographic information (maternal report)

Questions in the GAD Study parent interview were used to assess total family income, mother’s marital status, mother’s highest level of education and mother’s general health, for consideration as covariates in analyses.

For family income, a dichotomous variable was created to reflect whether or not the family could be considered to have a low income relative to Australian standards. “Low income” was defined as an annual pre-tax income in the lowest population quartile, which equated to approximately $35,000 per annum. For marital status, a dichotomous variable was created to reflect whether or not the mother was married or in an equivalent long-term de facto relationship. For education, a dichotomous variable was created to reflect whether or not the mother had completed high school. For maternal health, mothers rated their current physical health on a 5-point scale ranging from “poor” (1) to “excellent” (5).

Maternal and child Body Mass Index (BMI)

Height and weight were measured during the GAD Study interview. For mothers, BMI was calculated using the standard formula (weight [kg]/height [m]2). For children, age- and sex-specific BMI z-scores were calculated using the CDC 2000 reference data[80].

Statistical analyses

Responses to the EDE and GAD Study interview questions were used to categorise mothers into one of three groups: an eating disorder group, if they met criteria for a current eating disorder on the EDE or had a previous eating disorder as diagnosed by a health professional; a psychiatric control group, if they had a current or previous non-eating related psychiatric disorder as diagnosed by a health professional; or a general control group, if there was no evidence of a current or past eating or psychiatric disorder. Groups were compared on maternal and family factors.

To address Aim 1, linear mixed models were constructed to examine the effects of maternal group (eating disorder vs. psychiatric control vs. general control) on early child feeding practices (breastfeeding duration, age of introduction of solids), child eating disorder symptoms, child psychological functioning, general child health, and level of maternal concern about child weight. Mixed linear models allow grouping variables (i.e., family status) to be controlled for, meaning that any effects of clustering of children within families could be accounted for in the analyses. These models considered the effects of maternal group on early child feeding practices as reported at a single time point (retrospectively assessed at baseline) and childhood variables as assessed annually from baseline to 2-year follow-up. Support for Hypothesis 1 would come from children of mothers with a past or current eating disorder showing greater eating disorder symptoms, on average, over the 2-year study period than children of mothers in the psychiatric and general control groups.

To address Aim 2, linear mixed models and generalised estimating equations were used to identify significant predictors of changes in child eating disorder symptoms over time. Continuous outcome variables (for use in linear mixed models) included ChEDE Brief Global scores and Restraint scores, and CARES emotional eating scores. The categorical outcome variable (for use in generalised estimating equations) was loss of control eating. Time invariant and time-varying family factors were considered as predictor variables and child BMI z-score was included as a covariate in all multivariate models.

Time invariant predictors were those variables assessed at baseline only, or which showed considerable stability over the 2 year assessment period and so were used at baseline only. These included maternal group (eating disorder vs. psychiatric control vs. general control) and level of maternal concern about child weight (no concern vs. slight concern vs. moderate-high concern) as family predictor variables, and family income (low vs. medium-high), mother’s marital status (married/de facto vs. no long-term relationship) and maternal education (high school vs. less than high school) as potential covariates. For these variables, associations were between the predictor variable at baseline and average levels of the outcome variable over the 2 year study period. A significant interaction between a time invariant predictor and time would show that the predictor variable at baseline predicted changes in the outcome variable over the subsequent 2 years.

Time-varying predictors were those variables that were assessed annually from baseline to 2-year follow-up, and which showed variation over the assessment period. These included scores for the EDE Brief Global scale, DASS, RSES, Life Event Scale, Parenting Scale, McMaster Family Functioning scale and SLSS, as family predictor variables, as well as maternal BMI as a potential covariate. For these variables, associations were between changes in the predictor variable over the 2 year study period and changes in the outcome variable over the same time frame.

Predictors were initially examined in univariate models, and those that were significant at p < .05 were later entered in multivariate analyses. As note, all multivariate models included child BMI z-score. In addition, a more complex model was specified that included child BMI z-score as well as child depressive symptoms and global self-esteem. If family factors predicted child eating disorder symptoms after depressive symptoms and self-esteem were accounted for, evidence would be provided for a specific association between family factors and child eating disorder symptoms.

Models were constructed for boys and girls together, with gender interaction terms used to explore possible gender differences in the degree or nature of associations between variables. Consistent with recommendations, analyses were initially conducted using non-interaction variables only and subsequently conducted using non-interaction and interaction terms[81]. Interaction terms were only retained if they contributed to a model significantly.

Support for Hypothesis 2 would come from mother’s DASS scores being significant longitudinal predictors of increasing child eating disorder symptoms. Support for Hypothesis 3 would come from mother’s McMaster Family Functioning scores and/or children’s SLSS family satisfaction scores being significant longitudinal predictors of decreasing eating disorder symptoms.