Diet, Exercise and Motivation in Weight Reduction:
The Role of Psychological Capital and Stress
Mary Sophia Barnes and Tony Cassidy*
School of Psychology, Ulster University, Coleraine, Northern Ireland
Submission: October 26, 2018; Published: December 10, 2018
*Corresponding author: Tony Cassidy, School of Psychology, Ulster University, Coleraine, Northern Ireland.
How to cite this article: Mary S B,Tony C. Diet, Exercise and Motivation in Weight Reduction: The Role of Psychological Capital and Stress. JOJ Nurse
Health Care. 2018; 9(5): 555775. DOI: 10.19080/JOJNHC.2018.09.555775.
This study tested the impact of diet, exercise and motivation on weight loss, stress, and health behaviour over 12 weeks, and also the predictability of the composite factor of psychological capital (self-efficacy, optimism, hope and resilience) for outcomes. 241 females between the ages of 18-35 years attending university who wanted to lose weight were recruited at week one. 141 remained at week 12. Participants were allocated to one of three groups, group 1, diet only, group 2, diet and exercise, and group 3, diet exercise and motivational interviewing (MI). Across all measures, group 3 (diet, MAA and MI) showed greatest effect, as well as for weight loss. PsyCap was not found to be a predictor of success, however, it was found to have significantly improved for group 3 at time 2. Implications for weight loss interventions for females experiencing stress at periods of low support are discussed.
Prevalence of overweight and obesity in populations, and associated comorbid diseases such as diabetes mellitus, osteoarthritis, coronary heart disease, hypertension, and stroke are now so great as to have overtaken undernutrition and infectious diseases as the leading cause of ill-health in the twenty-first century [1,2]. In the US, two-thirds of the population are overweight and obese, and in Ireland thirty-nine percent of the adult population were found to be overweight, with eighteen percent obese .
The economic costs and burdens of obesity include costs to service providers, the individuals themselves, the opportunity cost to the individual, and indirect costs resulting from poor health, and premature death . The social cost of obesity is found in prejudice directed at persons with obesity resulting in the unequal treatment in relation to access to healthcare, education, and employment . Also, the stigmatisation of persons with obesity has been found to result in negative psychosocial behaviours such as social avoidance . There is, therefore, a pressing need to treat overweight and obesity so as to prevent the many direct, and indirect long-terms costs to individuals, and their health. It is imperative that individuals at risk of overweight and obesity are encouraged to access interventions to reduce weight as early as possible in the lifespan in order to prevent detrimental consequences to health and well-being over the long-term.
A review of weight management interventions found that inclusion of routine physical activity is essential for both short-term and long-term weight loss but only when combined with calorie restriction . Behaviour change techniques in weight-loss treatments aim to improve coping, and focus on changing
eating behaviours, activity levels, and thinking patterns that contribute to obesity .
It was found that the treatments of diet restriction, exercise, and behaviour change when combined, result in a clinically significant 10% reduction in weight in the short-term, and more significantly, a reduction in binge eating and depression in women. One such technique utilised for behaviour change is that of Motivational Interviewing (MI). MI is a collaborative, supportive, client centred practice, dedicated to improving motivation and commitment to behavioural change by encouraging the setting and implementation of goals .
It has largely been utilised in treating substance abuse disorders but has also been integrated successfully into weight management programmes with a reduction in drop-out rates compared with standard self-help interventions . A systematic review and meta-analysis of MI in randomised controlled trials found significant differences in weight loss for those in the MI group compared with controls  Booth, Prevost and found that weight management interventions in the UK were largely accessed by women, older patients, and those with comorbid conditions, and that follow up intervention was infrequent. The growing burden that overweight and obesity present requires targeted and early interventions for groups identified as being at risk for developing these conditions.
One such group are students attending university  first year in particular as a “critical period for weight gain”. Twenty-five percent of first year students were found to have gained a clinically significant 2.3kg during the first semester, with a doubling in numbers gaining weight during the second semester  Lifestyle changes identified as contributing to weight gain
include, consumption of high-fat foods instead of fruit and
vegetables, neglect of exercise, and increased alcohol intake .
Psychosocial pressures as a result of moving away from home and
established social supports, pressure to develop new friendships,
and academic pressures also increasing stress levels impact on
weight gain most notably in female students [9,10] found that
social support helped males transitioning to college to moderate
stress eating, but not females, as females required closer more
established support compared to males.
There is a long and substantial literature on stress and coping
 which has more recently focused on a resource approach
based on the construct of psychological capital . Traditionally
health psychology has focused on the deficit model of stress and
how health is compromised by stress . However, the resource
model, rooted in positive psychology, proposes that stressful
events can be mediated by psychological variables such as
psychological capital, social support, benefit finding, and positive
health or wellbeing [11,13] composite factor of psychological
capital connecting hope, optimism, resilience, and self-efficacy
represents what the authors describe as “an individual’s appraisal
of circumstances and probability for success based on motivated
effort and perseverance”.
The effect of stress and emotional eating has been found to be
greater in women, is a contributor to the diversity in individual
differences in success rates during weight loss interventions and
has been found to be a predictor of weight gain amongst students,
most notably females [10,14-16] set out to identify the factors
that separate males and females who overeat during stress from
those who do not. Although no gender differences were identified
with respect to intake, women compared with men were found to
demonstrate greater impulsivity to eat during stressful periods as
a consequence of disinhibition in disregarding self-imposed rules,
as measured on the Eating Inventory scale .
Furthermore, women who had reported disordered eating
behaviours, and more severe binging episodes were found to
overeat during stressful experiences.  found that predictors of
stress-related eating were different for men and women. Men were
found to be more at risk when single, divorced and unemployed,
and were more likely to consume alcohol as the level of stress
eating and drinking increased. Women were found to be at greater
risk due to low levels of emotional support. Furthermore, women
who craved chocolate were identified as having strongly negative
mood states, and as a consequence were more inclined to stress
eat and develop obesity .
The role of stress as a significant contributor to overweight
and obesity cannot be ignored as it is demonstrated to trigger the
binge eating of unhealthy foods strongly related to obesity .
Given, therefore, that women are at greater risk of weight gain as
a result of impulsive stress and emotional eating, most notably
during periods lacking in emotional support, programmes
designed to prevent and treat obesity should be targeted and
include strategies to assist better emotional coping through
development of cognitive restraint. Evidence supports the
view that weight management is complex. Understanding the
multiplicity of variables and individual differences in perceived
stress, psychological capital, lifestyle and resilience is essential
to improving outcomes for weight loss and maintenance of a
healthy weight. This study, therefore, will target female students
attending university, as this is a period of intense psychosocial
pressure. Students will be allocated to three different weight
management programmes, diet only, diet and exercise, and diet,
exercise and MI, to identify which type of intervention is most
likely to deliver success in weight loss through improvements in
lifestyle, stress management, psychological capital and resilience.
It is expected that MI will have the most significant effect on the
This study seeks to test the impact of three different
interventions (diet information only, diet information and
moderate aerobic activity, and diet information, moderate aerobic
activity and motivational interviewing) on weight loss, stress,
and health behaviour over 12 weeks, and to test if psychological
capital (self-efficacy, optimism, hope and resilience) would be
predictive of outcome.
This is a short-term longitudinal randomised control intervention
using 3 (conditions) x 2 (time-points) design. The first
outcome variable will be weight lost, and the predictor variable is
Psychological Capital (PsyCap).
A total of 241 female students between the ages of 18-25 years
responded to an e-mail circulated to 2,300 students via the Ulster
email system. The e-mail sought to recruit females between the
ages of 18-25 years who wanted to lost weight. Exclusion criteria
were those aged under 18 or over 25, those already engaged in a
weight loss intervention, males, and those with no desire to lose
weight. A link to an online questionnaire was emailed to all 241
responders. Using height and the weight screening tool of Body
Mass Index (BMI) scores, participants were randomly allocated to
one of 3 conditions: A) diet information only, B) diet information
and MAA, and C) diet information, MAA and a motivational
A PDF attachment providing dietary information and guidance
was sent to all participants (Appendix 2.1). This was repeated at
3-week intervals for a total of 12 weeks. Additionally, participants
in conditions B and C were supplied with information on the
benefits of moderate aerobic activity (MAA), and how to achieve
it, and were requested to record a minimum of 150 minutes of
MAA per week. Over each of the individual 12 weeks, participants
were contacted via email which asked for details of minutes
recorded for MAA that week. Participants in condition C were
invited to attend a 3-hour group based Motivational Interviewing
session and were provided with a questionnaire facilitating selfreflection
based on motivational principles every third week. All participants were assessed before the intervention and also at the
end of the 12 weeks on the measures below. By the end of the 12
weeks, only 141 participants remained, 42 in group 1, 32 in group
2, and 67 in group 3.
The Perceived Stress Scale – 10 item , developed from
the 14 item Perceived Stress Scale (PSS)  is a measure of
how unpredictable, uncontrollable, and overloaded an individual
perceives their life to be (Appendix 5). Based on the theory of
stress appraisal  the PSS is a measure of the “degree to which
situations in one’s life are appraised as stressful . Internal
consistency for the PSS was strong (α= .86).
This composite construct consisting of the four factors of
hope, resilience, optimism, and self-efficacy has been utilised
as a psychometric tool to predict work performance and job
satisfaction . PsyCap is described as a “positive state-like
capacity” that can be positively enhanced through support 
The study used the PCQ-24 measure (α = .89) .
All four component factors were measured using 6 items.
Participants were asked to rate how they feel about themselves
in order to establish their state-like capacity at that moment.
For example, self-efficacy (α= .85): ‘I feel confident helping to set
targets/goals in my work area’; hope (α = .80):‘I can think of many
ways to reach my current work goals’; resilience (α = .72): ‘I can
usually take stressful things at work in stride’; optimism (α = .79):
‘When things are uncertain for me at work, I usually expect the
best’. The Self-Rater Version was used with agreement rated on
a 6-point Likert-type scale (1 = strongly disagree to 6 = strongly
Permission to conduct the study was granted by the Ulster
University Filter Committee. The study was designed in accordance
with the British Psychological Society’s  and the ethical
standards of Ulster University for research with human participants.
Following completion of data collection, the four scales for
each participant were scored and entered onto SPSS for analysis.
Descriptive statistics were examined to identify the mean and
standard deviation for each group and each of the four measures
at both time 1 and time 2. A mixed model Anova with repeated
measures across time and between participants for the three
conditions was conducted to test for main effects and interactions.
A one-way Anova was used to test for baseline differences between
the groups and the four outcome variables.
This study tested the effect of three different weight loss
interventions on weight loss, stress and health behaviour over
12 weeks, and tested whether psychological capital is predictive
of outcome. The first stage of analysis resulted in the calculation
of descriptive statistics for stress, health action, weight and
psychological capital by group and time, and are outlined in Table
The second stage of analysis was to use a mixed model Anova
to test for main effects and interactions with repeated measures
across time, and between participants on the three conditions.
For stress at times one and two there was a significant main effect
(F(1, 138) = 14.688, P<.001, np² = .096). The partial eta squared
(np²) of .096 is between a medium and large effect size. Cohen’s
(1988) rule of thumb suggests that 0.01 = small effect, 0.06
= medium effect, and 0.14 = large effect. A significant stress by
group interaction was also found (F(2, 138) = 4.158, p<.05, np²
= .057), and the partial eta squared (np²) of .057 falls between
medium and large effect. Mixed Anova was again used to test
weight at times one and two.
A significant main resulted (F(1, 138) =77.812, p<.001, np²
=.36). The partial eta squared (np²) of .36 shows a large effect
size. A significant weight by group interaction also resulted (F (2,
138) =21.837, p<.001, np² = .24). Mixed Anova was also used to
test health action at times one and two. There was a significant
main effect (F (1, 138) = 35.97, p˂.01, np² = .21). The partial eta
squared (np²) of .21 demonstrates a large effect size. Health action
by group interaction was also significant (F (2,138) = 5.439, p˂.01,
np² = .08).
Mixed Anova was also used to test psychological capital at
times one and two. There was a significant main effect (F (1, 138)
= 21.05, p˂.001, np² = .13). The partial eta squared (np²) of .13
demonstrates a medium effect size. Psychological capital by group
interaction was not significant. As 241 participants had started,
and only 141 completed the programme, a Chi-square test was
conducted to test any relationship between completing and the
experimental condition. A significant relationship resulted (chisquare
(2) = 19.718, p˂.001) demonstrating that participants
in the group of combined diet, exercise, and motivational
interviewing were more likely to complete the programme.
In order to check for baseline, bias a one-way Anova was
used to test for differences between the groups on stress, health
action, psychological capital and weight at time one. There were
no main effects. one-way Anova between the groups for stress,
health action, psychological capital and weight at time two show
main effects for stress (F(2,138) = 17.21, p<.001), health action
(F(2,138) = 21.99, p<.001), psychological capital (F(2,138) = 6.29,
p<.01), and weight (F(2,138 )= 7.43, p<.001). In addition weight
loss was calculated by subtracting weight at time 2 from weight at
time 1 and one-way Anova across groups showed a main effect for
group (F(2,138) = 29.13, p<.001).
This study tested the impact of three different interventions
for three groups,  diet information only,  diet information
and moderate aerobic activity, and  diet information, moderate
aerobic activity, and motivational interviewing, on weight loss,
stress, and health behaviour over twelve weeks. Also tested was
whether the composite factor of psychological capital would be
predictive of outcome. No differences were found between the
groups on weight, stress, health action and psychological capital
at the commencement of the study.
In line with expectations, a main effect for each of the three
groups was found between times one and two for weight, stress,
and health action, with the motivational interviewing condition
showing the greatest effect for these measures. Furthermore, it
was found that those allocated to this condition were more likely to
complete the programme. In particular, results show a significant
effect for weight loss in each of the three groups. Weight loss
differences by group were also observed, with the most significant
weight loss occurring in the MI condition, followed by group two,
diet information and MAA. The least amount of weight lost was
observed in group one, diet only. The finding of greater weight
loss for the MI condition is consistent with a number of reviews
which have found that behavioural approaches to weight control
result in more successful and sustained weight loss [7,20-25].
Behaviour programmes restricting dietary intake, undertaking
regular exercise of between 150-200 minutes minimum per week,
and self-monitoring as conducted in this study for groups two and
three, have been identified as being associated with improved
weight loss . Furthermore, the provision of dietary information
and guidance at three weekly intervals over the twelve weeks to
each of the three groups in this study likely encouraged positive
cues for eating healthy food for all participants. Such cues are
found to encourage the removal of high fat/high calorie foods from
places of residence and increase positive behaviours around the
provision of low-calorie alternatives [25-32]. This could explain
why weight loss was significant for all three groups.
Equally, the provision of information on the benefits of MAA
in its different forms, the recording of MAA by groups two and
three, and the weekly recording of MAA by email is supported by
evidence for the combination of diet and exercise for successful
weight loss, over exercise alone, . The inclusion of selfmonitoring
further promotes more successful weight loss .
Groups two and three undertook and recorded a minimum of
150 minutes of exercise per week. However, participants were
not directed as to how often to exercise.  review examined the
question as to whether several short bursts of exercise were more
efficient for weight loss compared with one long bout of exercise,
finding that short bursts were as beneficial for weight loss as
one long bout of exercise. Thus, it is likely that any differences in
the scheduling of exercise were unlikely to have interfered with
results. Rather, it is the inclusion of exercise as a lifestyle change
that is beneficial for weight loss. The inclusion of motivational
interviewing (MI) resulted in a significant difference in weight
loss for this group. Weight loss was twice that achieved in group
two, and eight times more than that in group one (Table 1). This
finding is consistent with  review which identified MI as having
a medium effect on weight loss.  assert that the directive,
patient-centred counselling approach of MI is appropriate for
weight loss programmes as it promotes greater focus on the
goal of weight loss. Although MI has most commonly been used
in the field of addictions to motivate for change, and to promote
adherence, its usefulness in weight loss is focused on behaviour
modification rather than on the cessation or total abstinence from
a substance . There is, therefore, a difference in how it is applied
for weight loss. Furthermore,  found that MI and behavioural
interventions combined tended to result in greater weight loss
than for minimal intervention control groups. Again, this finding
is consistent with the present study. The centrality of weight loss
as the principal goal as opposed to a fitness goal, a dietary goal, or
a health status change goal such as lowered cholesterol is key to
greater weight loss .
MI has also been found to promote adherence, a strong
predictor of weight loss . In this study, there was a significant
finding for participants in the experimental group completing the
programme and achieving greater weight loss. It could, therefore,
be concluded that adherence in terms of diet, exercise, and the setting of goals all improved due to the MI. The inclusion of MI
in the experimental condition certainly resulted in greater weight
loss, and significant effects across all measures.
A significant effect for both stress and health action was found
at times one and two over the twelve weeks, and a significant
effect for stress and health action by group with the greatest
reduction in stress observed in the experimental condition. The
next greatest reduction in stress occurred in group two, followed
by group one. The bi-directional relationship between stress and
the consumption of high calorie foods in females during periods of
high stress is well documented . Binge eating can be a serious
confounder for weight loss. As participants in this study were all
females attending university, a period of time associated with low
emotional support, it is noteworthy that participants in group
3 (MI) experienced the greatest reduction in stress, and highest
scores for positive health behaviours. This indicates that both
health behaviour and adherence were improved by MI.
The second question asked pertained to the predictability
of the composite factor of psychological capital (PsyCap), made
up of hope, resilience, optimism, and efficacy. As there was no
significant difference between the groups for psychological
capital, it was found not to be a predictor of success. There was,
however, a significant main effect for improvement in this statelike
construct between times one and two for the experimental
condition, with a medium effect for group two. The rationale
for using PsyCap as a predictor of success was due to this
construct’s usefulness in identifying resources within individuals
which would improve that individual’s positive appraisal of
circumstances, thereby improving the probability of success .
The state-like element demonstrated effect. The predictability of
the measure did not. Furthermore, two measures were used to
test for psychological capital, the PCQ-24 and the Brief Resilience
Scale (BRS). Resilience was identified as an important component
of PsyCap as it measures just how strongly participants were able
to recover from stressful events, adapt, and continue to adhere
to the weight loss programme. Consequently, this study’s design
included a second measure to compliment PsyCap. The fact that
greater numbers completed the study from the experimental
group than from the two other groups indicates that resilience
developed between times one and two However, as resilience is
likely to have developed considerably as a consequence of the
intervention, a question remains as to whether the inclusion of
the second measure of the BRS favoured the state-like element
over the predictive.
This study’s findings could be useful for the design of
targeted weight loss interventions as part of a stress management
programme for females through university health centres or
indeed in an occupational health setting. Supporting female
university students through the adjustment of moving away from
home, and social supports during the first year of university is
important, as this is a period when students are vulnerable to
weight gain  Nonetheless, longitudinal research using a more
diverse sample, and similar design and measures, including one
for binge eating, is needed. Such a study would test firstly, the
effect of disinhibition on binge eating on adherence and weight,
and secondly, test for long-term weight maintenance, and finally,
test for the predictability of psychological capital.