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.