Investigating psychosocial predictors of diet adherence behaviour in a group of obese and non-obese individuals: A study of a battery development and a model testing with in the scope of Theory of Planned Behaviour

According to World Health Organization (WHO), obesity is defined as an excessive accumulation of fat causing harms on person's body and health (WHO,1997) due to genetic, environmental and psychosocial influences. As obesity comes along with various medical problems, it is a chronic disease that should be treated. One of the common treatments for obesity is dieting. Research findings show that people at risk have difficulties in starting and adapting to a diet which is defined as diet adherence behaviour. Main goal of this research is to develop a diet adherence behaviour battery in order to investigate the psychosocial predictors of diet adherence behaviour within the scope of Theory of Planned Behaviour (TPB). The second aim of this research is to test the major premises of TPB which suggests that attitudes, subjective norms and perceived behavioural control, which are considered among TPB structures, predict behaviour via intention in directly and that the strongest predictor of behaviour is the intention. The Theory of Planned Behaviour Diet Adherence Battery (TPBDA): consists of two index measures and 13 scales evaluating attitudes, subjective norms, perceived behavioural control, intention and behaviour structures. Validity and reliability of the battery scales have been carried out with 303 participants from psychology students at Istanbul University and Istanbul Kültür University. Their ages ranged between 18 and 59. With in the scope of reliability, internal consistency coefficients were calculated. For the validity of the battery scales, factor analysis were carried out after running item analysis. Correlation coefficients of the scales included in the battery, with each other and with Eating Disorder Examination Questionnaire (EDEQ), Eating Attitude Test (EAT-26), Patient Health Questionnaire (PHQ), Short Form Health Survey (SF-36) and Diet Self-efficacy Beliefs Scale (DSBS) were also examined. With respect to discriminative validity, obese (n=17) and non- obese (n=286) participants were compared in terms of mean scores received from TPBDA scales. According to the results, the final version of the battery consisted of a total of 68 items. The scales included in TPBDA were observed to have expected values of validity and reliability. In line with the expectations, it has been observed that strongest predictor of diet intention was indirect attitudes and the strongest predictor of diet adherence be haviour was intention. It has also been found that behavioural intention partial mediating role on the relationship between attitudes and perceived behavioural control with behaviour. To conclude, these findings can be accepted as evidence for the validity and reliability of the battery and TPB predictions. These findings suggest that especially attitudes and self-efficacy constructs should be taken into consideration while planning TPB based intervention programs with respect to diet adherence behaviour.