Obesity represents a significant individual, public health and economic issue.Recent data estimates that 39% of the world’s adult population is overweight, with a further13% estimated to have obesity[1]. Importantly, obesity significantly increases the risk of numerous non-communicable diseases including diabetes, cardiovascular disease, osteoarthritis, some cancers and mental health issues[2].It is, therefore, unsurprising that research in recent years has focused on understanding the factors contributing to obesity and ways to prevent, and treat obesity, both at an individual and public health level. The development of obesity is of multifactorial origin, with complex interactions occurring between various contributing factors. Extensive research has identified associations between obesity and genetics, epigenetics, alterations in gut microbiome, behavioural, sociodemographic and psychological factors [3-5]. Various types of psychological stress have been linked to increased body mass index (BMI) [6],with an association between stress, negative emotions and subsequent maladaptive coping mechanisms such as overeating [7]. Furthermore, individuals with higher BMIs have been shown to be at risk of significant social and psychological stress, as a consequence of weight discrimination[8] and social inequality with respect to income and educational levels [9]. However, despite an established correlation between obesity and psychological factors, currently both individual and public health initiatives tend to focus primarily on behavioural contributors[10, 11]. The potential association between locus of control and obesity, and utility for management of obesity is an important area for investigation. The concept of “locus of control” (LOC)was first introduced in Rotter’s social learning theory and refers to an individual’s belief about the degree of control they have over their own life. It wasoriginallyconceptualised along a continuum from internal to external control [12].Internal control (ILOC) refers to the belief that there is a causal relationship between an individual’s own behaviour and an event. External control (ELOC) refers to belief that an event is a result of external forces and not entirely dependent on his/her own actions[12].In contrast to Rotter’s internal-external model, the subsequent development of a multidimension health LOC, further divided externality into two distinct dimensions – Powerful Others (incorporating doctors and other health professionals) and Chance[13]. Importantly, this seminal work by Rotter, has been followed by several studies that have highlighted problems associated with the measurement of locus of control[14, 15].Furthermore, although LOC has mostly been considered a stable trait [16], some studies have suggested that LOC may be malleable;with increased ILOC following health screening[17]and reduction in ELOC following stress management interventions[18].Importantly, it has been proposed that an individual’s LOC impacts their risk of obesity, although there is controversy regarding how to best measure LOC and whether there is indeed a causal and modifiable relationship present[19, 20]. Numerous tools, of varying utility and validity, have been developed to measure Locus of Control, in relation to obesity.Common “Locus of Control” models include, but are not limited to,the Multidimensional Health Locus of Control Scale (MHLCS), Weight Locus of Control Scale (WLOCS), and Dieting Beliefs Scale (DBS). The Multidimensional Health Locus of Control Scale (MHLCS) was established in 1978, consisting of two parallel forms (A, B), with the addition of a third condition-specific form C in 1994, that can be easily adapted for people with different existing medical (or health related) conditions [13]. Subsequently it was adapted in 1982 to form theWeight Locus of Control (WLOC) scale, with the aim of better predicting success of weight control [21].Furthermore, the Dieting Beliefs Scale (DBS) was established in 1990 as an alternative measure of weight locus of control [22]. In addition to these models, other terms such as ‘autonomy’ and ‘self-efficacy’ have also been used to describe similar individual psychological characteristics [19]. Each measure varies slightly with respect to items included, subject population and validity, however, this beyond the scope of this review. Evidence regarding a potential interaction between LOC and obesity has been mixed.Although there is controversy regarding a potential causal relationship, most research supports at least a correlation between LOC and obesity [23]. Subsequently, numerous mechanisms have been proposed. An internally orientated LOC has been found to be associated with a lower overall mortality [24], attitudes more favourable to changes towards healthier lifestyles [25], healthier habits and greater weight loss [26, 27].Additionally, links between external LOC, higher BMIand poorer psychological wellbeing have also been described[28, 29]. It has been suggested that an internal LOC may be protective, whilst an external LOC may contribute to obesity risk. However, some studies have identifiedno correlation between LOC and body size, despite evidence of a correlation between LOC and psychological wellbeing [30, 31]. Interactions between sociodemographic characteristics, value of health and LOC have also been described but require further examination. This raises the question, does LOC have a direct correlation with obesity? Or rather,is its impact, more indirect through established risk factors for obesity such as sociodemographic, psychological and behavioural components? The primary aim of this review was to examine the evidence for an association between LOC and risk of obesity, within adult populations in developed countries.Risk of obesity will include such indirect factors as weight loss and weight loss maintenance, health-related behaviours, sociodemographic and psychological factors. The secondary aim of this review was to assess evidence of LOC being amenable to change and thus the utility of targeting LOC in the context of prevention and management of obesity.

Search strategy

Key words were identified through a general search of existing literature via PubMed prior to performing the systematic search; with subsequent refinement during preliminary searches.For the final search, the follow key terms were used: “locus of control”, obesity, overweight. Phrase searching with quotation marks was utilised for “locus of control” in order to accurately search the term. Boolean operators were utilised to ensure articles were relevant to both locus of control AND obesity, with the use of OR obesity OR overweight, in order to enable a more comprehensive search. The search included articles published in English language during the timeframe of 2010-16th March 2021(Table 1). The cut-off of 2010 was chosen, as new clinical guidelines for use in Australia were commissioned at this time, and included consideration of psychological factors in obesity management [32].Relevant studies were identified through a comprehensive search of PubMed and PsychINFO (Ovid) databases.

Table 1: Search strategy.

Inclusion and Exclusion Criteria

Studies included in the review were required to meet the following inclusion criteria: Adults (18+ years), non-pregnant, developed countries, English language, publication date 2010- 16th March 2021. Studies were excluded for the following reasons: study participants <18years, pregnancy, developing countries, not available in English language, publication date prior to 2010, secondary-data,non-peer viewed. Further studies were excluded based on poorly defined LOC measures or a primary focus other than LOC and obesity.

Data Analysis and Synthesis

The review was prepared in accordance with the PRISMA statement. The original search yielded 130 articles from PubMed (n= 59) and PsychINFO (n=71); duplicates (19) were removed, and articles were subsequently screened based on title and abstract. 85 articles were excluded based on title and abstract. 26 full-text articles were then reviewed using the most relevantJoanna Briggs Institute (JBI) critical appraisal tool according to their study design[33]. 18 articles met inclusion criteria, with thereview based on full text analysis of these articles. These articles were assessed as high quality, peer-reviewed, primary data, with a well-defined measure for LOC and primary focus on the potential interaction between LOC and obesity.

Results

Overview of Results

Included studies were heterogenous with regards to setting, sample populations, study designs, primary outcomes and LOC scales. Studies were conducted in various different settings, with the majority conducted in the community (n=13). Of the 18 articles included in the final review, the majority (n=13) were observational in nature, with the remainder intervention studies (n=5). Primary outcomes included LOC scores, weight loss percentage and maintenance, eating habits, physical activity levels, psychological wellbeing, medical comorbidities and health-related quality of life.A variety of different measures of LOC were utilised throughout.

Table 2: Data extraction.

Key:

MHLC: Multidimensional health locus of control

MWLCS: Multidimensional weight locus of control scale

WLOC: Weight locus of control

HLC: Health locus of control

DBS: Dieting Belief Scale

LOC: Locus of control

Key findings

The evidence investigating an association between LOC and risk of obesity varied between studies. Included studies examined various aspects of obesity and LOC, including interactions with health behaviours, sociodemographic factors, psychological well-being, weight loss and weight maintenance. The capacity to alter LOC and attribution of obesity was also examined.Evidence of a correlation was variable. In general, an internally orientated LOC was reported to correlate with improved weight loss, weight loss maintenanceand healthier lifestyle behaviours, through observation in community settings[26-30]. In contrast, an externally orientated LOC was associated with a higher BMI, poorer psychological wellbeing and was postulated as a potential barrier to weight-loss[28-34]. Studies alsoreported that stress management interventions could assist in alteration of LOC and weight reduction[18].Furthermore, severalstudies highlighted the complex interaction between LOC and psychosocial/demographic factors, including education level, income level and food security[29-35].

Capacity to alter locus of control and attribution of obesity

The capacity to alter LOC or manipulate attribution of cause of obesity, has been examined. Studies looking at the association between BMI, locus of control, attribution of obesity and manipulation were heterogenous in nature.One study demonstrated that patients with obesity were more likely to attribute uncontrollable factors as the cause for their own weight and attribute controllable reasons for others’ weight [30]. Another study demonstrated that individuals with obesity were significantly more likely to attribute their weight to genetic causes [23]. However, neither study showed a significant correlation between BMI and LOC. A cross-sectional study looking at LOC and anti-fat attitudes, reported a significant correlation between MHLOC and anti-fat attitudes [36]. This suggests that individuals who believe health is within an individual’s control are more likely to hold anti-fat attitudes. Within the same study, BMI was reported to negatively correlate with anti-fat attitudes. This highlights the weight stigmatisation and belief that obesity is due to negative personal attributes such as laziness, predominately held by those with lower BMIs.However, no significant correlation between WLOC and anti-fat attitudes was reported. Another study showed that attribution of causes of obesity was manipulated by framing articles; although only in males [37]. Another study showed significant increase in Internal and Powerful Others LOC, following health screening [17]. Similarly, an intervention study showed reduction in chance LOC via implementation of a stress-management program [18]. Each of these studies highlight the potential for targeting LOC and attribution of cause of obesity.

Locus of Control and Health Behaviours

Locus of Control and Sociodemographic Factors

In the context of providing individualised treatment, a complex interaction between LOC, psychological and demographic factors have been reported. An associated between locus of control and sociodemographic factors was reported in two studies[29, 35].A cross-sectional study reported antenatal&childhood economic deprivation as predictors of an external LOC, alongside a positive correlation between external LOC and food insecurity. Additionally,an internal LOC was reportedly associated with a lower BMI [29]. Consequently, one may hypothesise that low socioeconomic status may be associated with an externally orientated LOC and increased risk of obesity, however,causality was unable to be determined using this methodology. Similarly, another cross-sectional studyreported a positive correlation between health LOC and both education and personal income levels. Interestingly,the same study reported a negative correlation between body satisfaction and education and income levels[35]. These results suggest that individuals of higher socioeconomic status simultaneously have higher health LOC scores and higher levels of body dissatisfaction. This potentially identifies a link between perceived ability to control one’s own weight and subsequent dissatisfaction with their attained weight. Extending upon this, one may speculate that this is also linked to poor psychological wellbeing, however, this was not examined in this study.

Locus of Control and Psychological Wellbeing

The association betweenLOC and psychological wellbeinghas been examined. It is important to note that many studies excluded patients with a history of mental health disorders, which limits the ability to look at psychological interactions withLOC.An association between external locus of control and poor mental health was demonstrated by two studies[29, 40], with a further study demonstrating a positive correlation between weight locus of control and psychological wellbeing[30].A cross-sectional study examining the interaction between obesity, psychosocial and sociodemographic factors reported that external LOC was associated with depressive symptoms[29]. Interestingly, in a studylooking at 40 post-bariatric surgery patients, it was reported that individuals who maintained the mindset that they were obese (‘I-obese’), demonstrated significantly higher Powerful others LOC and weight LOC scores, which negatively correlated with mental health and social functioning [40].This highlighted the importance of psychological adjustment following weight loss and the subsequent impact this has on psychosocial wellbeing. Another cross-sectional study explored the impact of social conditioningon self-perception and beliefs about causes of obesity [30].This study reporteda tendency for attribution of internal causes of obesity for others,but this did not hold true when considering the causes of their own obesity. Despitethis, the study did demonstrate a positive correlation between weight LOC and psychological wellbeing. Therefore, for individuals with obesity, their beliefs around the causes and controllability of their own obesity, differs from their beliefs for others, and may potentially beinfluenced by their psychological wellbeing.

Locus of Control and Weight Loss

Evidence of correlations between LOC, weight loss and weight-loss maintenance, were found to bemixed.Three of four studies reporteda correlation between locus of control and weight loss[18, 27, 31].Anobservationalstudyinvolving individuals who had previously intentionally lost 10% of their body weight, reported a positive correlation between an internal LOC, degree of weight loss and maintained weight loss [27]. These findings were supported by an intervention study, which also reported a positive correlation between internal LOC and weight loss and maintained weight loss within the control group[31]. This was a noteworthy finding as it identified internal WLOC as a predictor of weight loss. However, this positive correlation was not consistent within the study, with no significant correlation found for the intervention group, who had completed an educational program based on the self-determination theory. Rather, weight loss at 12 months was associated with fewer previous attempts at weight loss and maintained weight loss at 36 months was predicted by lower eating disinhibition and higher weight-related quality of life [31]. However, the intervention targeting self-determination may have mitigated an impact of the individual’s LOC. Similarly, another intervention study, involving an 8-week stress management course, reported no significant differences in LOC between the intervention and control group. However, the intervention group demonstrated greater weight reduction and higher levels of restrained eating[41], suggesting stress management may influence greater weight reductionvia alterations of eating patterns, rather than via manipulation of LOC.Contrastingly, another stress management intervention study, reported a significant difference in LOC between the control and interventional group; with the interventional groups demonstrating a significantly larger reduction in BMI and reduction in chance LOC [18]. This may suggest an indirect association between weight reduction and lower chance LOC scores, but due to the study design, no causal relationship was established.

Summary of Evidence

Many studies reported a correlation between obesity and LOC. However, there ismixedevidence about directionality of this association. In general, an internal LOC was associated with healthier lifestyle choices, lower BMI, and greater weight reduction and maintenance[26, 27, 30]. There is evidence of an association between an external LOC, poorer psychological wellbeing and lower sociodemographicstatus[28, 29].Furthermore, there was evidence of an interaction between psychological wellbeing, weight discrimination and LOC. Importantly, evidence demonstrated the potential to modify an individual’s LOC and beliefs surrounding causes of obesity. Inconsistency in findings may be due to differences in methodology, sample populations, measurement of LOC and the complex multifactorial nature of risk of obesity [19].

Locus of Control in Clinical Practice

There is potential for tailoring individual and public health interventions for the prevention and management of obesity, based on individuals’ LOC. Existing evidence reports a correlation between LOC and obesity, with some studies reporting capacity to alter an individual’s LOC. A study looking at health risks and locus of control following health screening, demonstrated a significant increase in ILOC and powerful others LOC following health screening [17]. Additionally, an interventionstudy implementing a stress management course demonstrated a reduction in chance LOC following the intervention[18]. The demonstrated capacity to alter an individual’s LOC, suggests possible utility in targeting an individual’s LOC as part of their management plan.

Strengths and Limitations

This review had several strengths including only incorporating high quality, peer-reviewed, primary evidence. Included studies also incorporated numerous age groups, cultural/ ethnic and sociodemographic groups, enabling a broader understanding of the contributing factors.Initially the searchterm locus of control did not include quotation marks, consequently identifying several studies focusing on genetic loci, however this was rectified in the final search.Limitations of thisreview include the risk of selection bias due to the nature of the review and absence of a second reviewer. Alarge degree of heterogeneity between studies was also present, making the comparison of current evidence more difficult. Additionally, the majority of studies were cross-sectional in nature (n=11) and subsequently only correlations rather than directionality of interactions could be examined. Furthermore, various measures of LOC were utilised, some of which were not previously validated. This occurred despite numerous studies already beingexcluded from the final review due to their poorly defined LOC.

Current research suggests a complex interaction between LOC,obesity and risk factors, which may have the potential to be targeted in the prevention and management of obesity.However, evidence for the mechanism of these interactions remains mixed and there is limited evidence demonstrating a causal relationship between LOC and obesity. Regardless, obesity prevention and management interventions focusing on modification of patient’s LOC, have the potential to be of benefit.However, further research is required to quantitatively evaluate outcomes of interventions targeting LOC.

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