To investigate the extent of baseline psychosocial characterisation of subjects in published dietary randomised controlled trials (RCTs) for weight loss.
Systematic review of adequately sized (n⩾10) RCTs comprising ⩾1 diet-alone arm for weight loss were included for this systematic review. More specifically, trials included overweight (body mass index >25 kg/m2) adults, were of duration ⩾8 weeks and had body weight as the primary outcome. Exclusion criteria included specific psychological intervention (for example, Cognitive Behaviour Therapy (CBT)), use of web-based tools, use of supplements, liquid diets, replacement meals and very-low calorie diets. Physical activity intervention was restricted to general exercise only (not supervised or prescribed, for example, VO2 maximum level).
Of 176 weight-loss RCTs published during 2008–2010, 15 met selection criteria and were assessed for reported psychological characterisation of subjects. All studies reported standard characterisation of clinical and biochemical characteristics of subjects. Eleven studies reported no psychological attributes of subjects (three of these did exclude those taking psychoactive medication). Three studies collected data on particular aspects of psychology related to specific research objectives (figure scale rating, satiety and quality-of-life). Only one study provided a comprehensive background on psychological attributes of subjects.
Better characterisation in behaviour-change interventions will reduce potential confounding and enhance generalisability of such studies.
Overweight and obesity have become a global health issue requiring urgent population-level intervention,1 because of direct links with increased risk of cardiometabolic diseases associated with metabolic syndrome, including coronary heart disease, hypertension and type II diabetes,2 as well as associations with cancer3 and musculoskeletal injury4 risk. There is substantial evidence that diet, physical activity and/or medication can reduce this risk.1
There are established links between affective disorders (for example, depression and anxiety) and cardiometabolic disease. Because depression has been identified as a major global public health issue with prevalence expanding steadily,5 depression may associate with various diseases simply on the basis of increased prevalence across the population. However, various studies have shown complex associations between depression and the cardiometabolic comorbidities of obesity and metabolic syndrome. Depression is associated with coronary risk directly6 and indirectly through effects on body mass index (BMI), diet, physical activity, smoking, medication treatment fidelity and various biochemical mediators.7, 8, 9, 10 Further, there are strong and consistent relationships between depression and obesity, physical activity and energy intake in middle-aged women,11 and between depression and physical activity in elderly men.12 Depression is also associated with increased risk of type II diabetes.13 Conversely, obesity and coronary heart disease both correlate with elevated depression risk.14 De Wit et al.15 have shown that relationships between depression/anxiety and obesity may be mediated partly through effects on physical and social activities.
The psychophysiological nexus is a conduit by which factors such as socioeconomic status, adverse life events and loneliness can affect stress-related inflammatory states.16, 17, 18 Major depressive disorder is associated with increased circulatory cytokines tumour necrosis factor alpha and interleukin-1,19 both of which contribute to ageing and chronic neurodegenerative disorders,20 and are risk factors for coronary heart disease.21 Conversely, positive affect induces beneficial neuroendocrine, autonomic and immune consequences.22 Affective disorders therefore have the potential to affect cardiometabolic risk through multiple pathways, and are therefore potential confounders where cytokine levels are primary outcome indicators.
In addition to confounding outcome variables, psychosocial attributes can affect who participates in research trials and how they engage with weight-loss intervention protocols. General associations between affective disorders (for example, depression and anxiety) and weight-loss success have been noted,23 possibly due to direct effects on adherence24 and/or trial drop-out.25
Various psychosocial factors thus have the potential to confound outcomes from and restrict the generalisability of results from dietary weight-loss trials. The purpose of this systematic review was to examine the extent of controlling for psychosocial characteristics of subjects reported in recent diet-centred non-clinical weight-loss trials where psychological strategies were not part of the actual intervention.
Materials and methods
Diet-based weight-loss trials published between January 2008 and January 2010 and cited via Medline were analysed for this review.
Computerised literature searches in PubMed and EMBASE electronic databases and Cochrane Central Register of Controlled Trials were performed. Search was limited by publication date between January 2008 and January 2010 and restricted to papers published in English language. Medical Subject Headings (MeSH) database was used as a terminological search filter. From the combination of terminological (MeSH terms) and methodological search filters (‘PubMed clinical queries’), relevant journal articles were retrieved. After a preliminary search of terms, the query ‘(weight loss (MeSH) OR) AND ((diet) (MeSH) OR dietary (MeSH limited to ‘Humans’))’ was used.
The bibliographic search was extended to the ‘Related Articles’ link next to each selected article in PubMed and its references. Finally, automatic alerts (up to 31 December 2009) (query 1: ‘weight loss (MeSH) OR’; query 2: ‘(diet) (MeSH)’ were activated in PubMed (‘My NCBI’) to add relevant articles published after the initial search.
Two reviewers (KM and MAF) independently assessed the extracted data (titles, abstracts, references and full-text articles). Chance-adjusted inter-rater agreement was calculated using Cohen k statistics (κ=0.95) and was found to be satisfactory. Discrepancy was resolved by consultation of a third reviewer not involved in the initial selection procedure (SS).
Eligibility of relevant studies
Randomised controlled trials (RCTs) comprising at least one diet-alone arm for weight loss in overweight (BMI >25 kg/m2 or abdominal adiposity) adults (⩾18 years) were included. Only studies with ⩾10 subjects with dietary intervention ⩾8 weeks using body weight as the primary outcome indicator were included.
Studies were excluded if supplements, liquid diets or replacement meals were used. Very-low-calorie diets were also excluded. Physical activity intervention was restricted to general exercise only (not supervised or prescribed, for example, VO2 maximum level). Studies which incorporated psychological intervention (for example, Cognitive Behaviour Therapy) or web-based tools were also excluded.
Also excluded were reviews, editorials, case reports, letters to the editor, hypotheses, studies on animals or cell lines, abstracts from conferences or otherwise unpublished studies.
Fifteen studies were selected for analysis in this study. General study characteristics are summarised in Table 1. All provided data on the basic anthropometric measure of BMI, and many a range of biochemical risk factors (see Table 1).
There was some reporting of basic social characterisation such as socioeconomic status, education, ethnicity and attrition rates (which ranged from 3 to 27.9%—see Table 2). Specific psychological methods were used to characterise subjects, but were used only when the associated factors were specifically relevant to the study outcomes. No data on factors related to depression, anxiety or stress were reported by any of the studies.
The focus of this study was on large, well-controlled dietary weight-loss trials of at least 8 weeks duration, which represent best practice in this area. These trials also utilised best-practice RCT principles of characterising groups to allow for comparison and minimisation of bias by adjustment for confounding variables.26 For all studies, the benchmark characterisation focussed on the primary outcome indicator of body weight. Most studies also incorporated biochemical outcome indicators related to coronary heart disease risk, such as serum lipid profiles (total cholesterol, HDL, LDL and triglycerides). More detailed serum chemistry (such as inflammatory cytokines and adipokines) depended on the specific context and primary outcome indicators of each study. Given the potential for affective disorders to affect inflammatory cytokine levels,19, 27 it is noteworthy that 4 of the 15 trials measured tumour necrosis factor alpha and interleukin-6,28, 29, 30, 31 which are known to be affected by psychological factors, but none assessed subjects for associated psychological attributes.
In terms of psychosocial characterisation of subjects at baseline, data collection could best be described as weak. Table 2 shows that even rudimentary data on socioeconomic factors, such as income and education, generally were not reported. Baseline psychosocial characterisation was either not collected or collected and not reported. Table 2 lists psychosocial variables reported. Key social demographic data, including income and education, were infrequently reported. Further, psychological attributes were rarely considered. Three studies excluded those taking psychoactive medication but did not measure the psychological characteristics of those recruited (see Table 2).32, 33, 34 This approach assumes that all affective disorders have been both diagnosed and prescribed for.
Four studies35, 36, 37, 38 used more sophisticated tools to assess psychological attributes. Specifically, Dennis et al.35 investigated hunger and satiety, Evangelista et al.36 used a quality-of-life questionnaire related specifically to heart failure, Vander Wal et al.38 applied a questionnaire targeting factors associated with binge eating and Fitzgibbon et al.37 used a figure scale rating to assess body image dysmorphia. These were specific to the aims and primary outcome indicators for each study, rather than an attempt to assess and describe the general psychological status of subjects in terms of affective disorders.
There is growing evidence that affective disorders such as depression, anxiety and stress, and related symptoms, can have an impact on established biochemical risk factors for metabolic syndrome.17, 19, 27 In the context of controlling for these potential confounding factors, all studies in the present analysis were less than adequate. Further, none of the studies included for analysis provided scope for post-hoc analysis to investigate the potential for psychosocial factors to mediate outcomes in dietary weight-loss trials. Currently, opportunities to target interventions to participants most likely to respond are being lost. In summary, psychological variables not accounted for could be confounding findings and diminishing effect sizes.
Another important aspect of psychosocial contexts of dietary behaviour intervention studies relate to the processes employed to recruit subjects, which can have significant potential to influence the profile of volunteers. The paucity of recruitment details reported compromises the ability to generalise results. This position is further weakened by only limited reporting of even very basic demographic characteristics, despite emerging evidence that domiciliary environment can affect chronic disease risk.39
Published studies of weight-loss interventions based on dietary behaviour change have only modest long-term outcomes.40 High attrition often occurs,41 and there are few longer-term trials reported.40 Low-dietary adherence that wanes progressively further over time is also of concern.42
The adherence phenomenon is affected by multiple factors, and psychological theoretical frameworks have been applied to understand the determinants of engagement in and adherence to weight-loss intervention by obese subjects. Such frameworks include Self-determination theory43 and the trans-theoretical model44 of change. Self-determination theory explains motivation and is underpinned by main elements of autonomy (ability and choice to act), competence (feeling competent to act) and relatedness (positive interactions with others as a result of acting).43 The trans-theoretical model44 also may influence weight loss,32 and is underpinned by five main stages of change (precontemplation, contemplation, preparation, action and maintenance and relapse prevention).44
However, such frameworks assume no underlying psychological pathology or dysfunction. Unipolar mood (affective) disorders (for example, depression and anxiety) and associated symptoms can affect participation in weight-loss trials. First, depression and anxiety can compromise dietary weight loss and maintenance success subsequent to behavioural23 and surgical interventions.33, 34 More specifically, both depression and anxiety symptoms can compromise dietary adherence24 and trial completion25 in dietary weight-loss trials. The potential for affective disorders to impact on treatment adherence may be expanding, because the prevalence of affective disorders such as depression is increasing in the general population.5
Potential mechanisms for affective disorders having an impact on trial drop-out and adherence are emerging. For instance, positive affect has been associated with restrained eating and reduced energy intake.45 In other studies, increased cognitive restraint was associated with weight loss46, 47 and weight maintenance.48, 49 Others have proposed that depression may reduce adherence through reduced social support, cognitive impairment and reduced outcome expectations.50, 51
Thus, there is potential for depression and other affective disorders to have a major role in influencing health-related outcomes via both behavioural mechanisms having an impact on treatment fidelity and through biological mechanisms (see Figure 1).
The substantial attrition rates reported in many weight-loss interventions, and the range up to 27.9% in studies investigated, compromise investment returns, when full trial costs are considered and compared with the quantity of usable data obtained. Because psychosocial variables were routinely either not collected or not reported, it is unclear whether any variation in attrition was attributable to these variables as usually they were not controlled for. Pre-assessment of affective disorders may be cost-effective to identify participants less likely to adhere to weight-loss dietary intervention. In a clinical setting, patients thus identified can be diverted to appropriate (pre)interventions. There is evidence that behavioural treatment for depression (that is, cognitive behaviour therapy) can affect adherence across a range of treatment modalities.52, 53, 54 Given the critical role of psychosocial factors in determining cardiovascular risk and adherence to behaviour intervention, Table 3 outlines steps to provide a framework for better design and reporting in such trials.
In this present systematic review, studies that had a psychological component embedded into their intervention arm were excluded. The intention of this was to examine the general ways in which subjects are characterised for weight-loss studies, rather than attributes being linked to study outcomes. The reason physical activity studies were excluded from the parameters was due to the established relationship between exercise and improved mental health in affective disorder.42, 55, 56 Combined dietary and exercise intervention for weight loss have also been associated with improved mental health.57 Such trends are not seen with dietary intervention. Because of this, affective disorders are more likely to remain consistent, and thereby have more impact on adherence and trial completion in a sole dietary intervention.
Study size in the present analysis ranged from 14 to 811 subjects. All studies used BMI to include/exclude subjects, notwithstanding the shortcomings in the utility of BMI to assess adiposity, especially in smaller populations. Many also used waist circumference, which may be a better indicator of obesity-related disease risk than BMI,58 as a further adiposity indicator. The smallest study36 (n=14) also used DEXA, which is a more sophisticated (and expensive) measure of adiposity. Five studies37, 59, 60, 61, 62 relied solely on BMI as an indicator of overweight. The choice of methods to assess adiposity is an important consideration in linking the outcomes of diet trials to chronic disease risk, rather than body-weight reduction alone.
This systematic review restricted study selection according to sample size, intervention focus and duration, factors that may limit generalisability. However, the emphasis of this analysis is on the methodologies that underpin dietary intervention trials specifically, and behaviour intervention trials more generally. In view of the strong associations between affective disorders and cardiometabolic comorbidities (and associated risk factors such as inflammatory cytokines and blood pressure), data on affective disorder status should be included in baseline characterisation of subjects, to control for potential confounding effects. In the clinical situation, such characterisation also is potentially useful in identifying likely candidates for early drop-out, so that such patients can be diverted to psychological preparation before dietary intervention.
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The authors declare no conflicts of interest.
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Cite this article
Somerset, S., Markwell, K. & Al-Foraih, M. A systematic review of baseline psychosocial characterisation in dietary randomised controlled trials for weight loss. Eur J Clin Nutr 67, 697–702 (2013). https://doi.org/10.1038/ejcn.2013.77
- weight loss
- randomised controlled trial
- psychological factors
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