Background
Behavioural interventions have demonstrated effectiveness in diabetes management, and theory-based interventions are more efficacious than non-theoretical approaches (Michie and Abraham, 2004). Several theories have been used to inform health behaviour change, including the Theory of Planned Behaviour (TPB) (Ajzen, 1991) and the Health Action Process Approach (HAPA) (Schwarzer, 2008). According to the TPB, a person’s behaviour is a function of intention to engage in the behaviour. In turn, the intention is directly determined by attitude (positive or negative evaluation of the behaviour), subjective norm (perceived pressure to perform a behaviour), and perceived behavioural control (PBC; perception of control over performing the behaviour, also said to influence behaviour directly). The direct TPB constructs also have a belief basis with advantages/disadvantages underlying attitude, important specific referents underlying subjective norm, and barriers/facilitators underlying PBC. The recent debate about the utility of the TPB in health psychology applications (Sniehotta et al., 2014) highlights the need to test the validity of the TPB. A recent meta-analysis demonstrated the effectiveness of TPB-based interventions in people with type 2 diabetes (T2D) (Steinmetz et al., 2016), with the effect size of 0.5 (CI=0.24 to 0.75) for behaviour. A TPB-based intervention among older T2D adults with cardiovascular disease found an extended TPB (with planning as an extra measure) intervention effective for improving physical activity but not healthy eating (White et al., 2012).
The HAPA is another theoretical framework focusing on motivational and volitional processes in health behaviour change (Schwarzer, 2008). Preintentional (motivational) processes target behavioural intention, and post intentional (volitional) processes lead to actual behaviour change. Perceived risk and outcome expectancies drive contemplation in the motivation phase, with self-efficacy also influencing intention. Schwarzer considers a minimum level of perceived risk necessary for the initiation of contemplation regarding the benefits of behaviour and one’s competence to perform the behaviour. For intentions to translate into behaviour, a volitional phase involving planning occurs, also underpinned by self-efficacy.
Moreover, perceived risk is a core motivational concept in many health behaviour theories, such as the Health Belief Model [HBM] (Rosenstock, 1974). It has been included in TPB studies (Brewer et al., 2007) to influence motivation for the initiation of mental preparedness for health change. Typical inclusions of risk perception measurement are risk severity (feeling the seriousness of contracting an illness or of leaving it untreated) and risk susceptibility (beliefs about the likelihood of getting a disease). Risk severity has been effective in predicting hemoglobin A1C (HbA1c) reductions in T2D participants (Daniel and Messer, 2002) and those with higher perceived severity and susceptibility were more adherent to self-care behaviours (Ayele et al., 2012, Tan, 2004).
In addition, planning has been suggested as a key volitional variable in behaviour change interventions (Sniehotta et al., 2005b, Norman and Conner, 2005), especially as it can mediate the intention-behaviour relationship (Norman and Conner, 2005, Luszczynska, 2006, White et al., 2012). According to the HAPA, the intention should be transformed into detailed instructions on how to perform the intended behaviour (action plans), which is necessary to prevent impulsive actions. Further, maintaining the initiated behaviour should be protected from barriers and obstacles by consideration, for example, of effective coping strategies (coping plans). It is believed that, via planning, individuals form a subjective instance of the target situation, which makes the target cue related to the situation more accessible and critical conditions easily identifiable (Gollwitzer, 1999). Planning has been previously assessed via action planning (enabling practical behaviour initiation via specifying a time, location, and how to perform the behaviour (Leventhal et al., 1965)) and coping planning (overcoming barriers by utilizing coping responses to deal with difficulties (Sniehotta et al., 2006)). Similarly, objective measures such as weight, body mass index (BMI), triglycerides (TG), and LDL-cholesterol (LDL-c) are essential components of comprehensive diabetes evaluation (ADA, 2019).
In a previous formative qualitative study among T2D (Blinded for review) we showed the inclusion of the standard TPB constructs (attitude, subjective norm, PBC), as well as risk perceptions and planning factors from the HAPA, which appeared viable as the focus of a behaviour change intervention among this cohort. To our knowledge, there is no TPB-based intervention among diabetes patients in Iran. Thus, the present study employed an integrated theoretical framework for informing and evaluating a behavioural intervention to promote low-fat food consumption, carbohydrate counting, and physical activity, three critical behaviours in diabetes management. We hypothesized that intervention participants would demonstrate an improvement compared to control participants at the end of the study, for (a) attitude, subjective norm, perceived behavioural control, intention, planning and risk perception for the three diabetes management behaviours, (b) the self-reported diabetes management behaviour, and (c) the behavioural indicators of weight, BMI, TG, and LDL-c.