Physical activity during weight loss and weight loss maintenance in men: an experimental application of social cognitive theory

Research Doctorate - Doctor of Philosophy (PhD)Background: Australian men are a high-risk group for weight-related disease. Although behavioural weight loss programs have well-documented short-term efficacy, longer term results are poor, most programs are too intensive for realistic dissemination, few are based in theory, and the vast majority have failed to engage men. Although additional ‘weight loss maintenance’ interventions have shown initial promise to reduce the rate of weight regain, the evidence base for these programs is limited by many of the same concerns. Further, while successful weight loss maintenance requires a clear and sustained increase in physical activity, little is known about which cognitive, behavioural, or social factors are most important to target in interventions to increase physical activity in men. Currently, an evidence gap exists for effective, theory-based weight loss and weight loss maintenance programs for men that could be realistically rolled-out at the population level. Objectives: This thesis-by-publication presents a series of studies that were conducted to address this gap in the evidence. Overall, these studies relate to: i) the utility of Bandura’s Social Cognitive Theory (SCT) to explain physical activity behaviour, and/or ii) the development and evaluation of the SCT-based SHED-IT (Self-help, Exercise and Diet using Information Technology) Weight Loss Maintenance Program for men. This program was designed to follow on from the previously established and evaluated SHED-IT Weight Loss Program, to provide men with new knowledge and skills to maintain their weight loss over time. Given the well-established importance of sustained increases in moderate-to-vigorous physical activity (MVPA) for weight loss maintenance, the primary aim of this thesis was to evaluate the effects of the SHED-IT Weight Loss Maintenance Program on men’s MVPA cognitions and MVPA behaviour, 12 months after successfully completing the SHED-IT Weight Loss Program. The thesis also presents a series of studies investigating five key secondary aims, which are briefly described below. Asthese studies provide important context for the primary analysis, the secondary aims are presented first in this thesis, in the following order: Secondary Aim 1: To synthesise the current evidence base regarding the effectiveness of male-only weight loss and weight loss maintenance interventions. To investigate this aim, a systematic literature search with no date restrictions was conducted across eight databases. In total, 24 articles describing 23 studies met the eligibility criteria. A fixed effects meta-analysis revealed a significant difference in weight change favouring weight loss interventions over no-intervention controls (weighted mean difference -5.66kg [-6.35,-4.97]), but study quality was mostly poor. Characteristics common to intervention effectiveness were: younger sample, increased contact, group face-to-face contact, and prescribed energy restrictions. Secondary Aim 2: To systematically review the evidence for the utility of Social Cognitive Theory as a framework to explain physical activity Ten electronic databases were systematically searched. Overall, 44 studies were retrieved containing 55 SCT models of physical activity. A random-effects metaanalysis revealed that SCT accounted for 31% of the variance in physical activity, but overall quality was poor. Methodological quality and sample age moderated the effect size for physical activity, with better quality and a higher mean age associated with greater variance explained. While self-efficacy and goals were consistently associated with physical activity, outcome expectations and socio-structural factors were not. Secondary Aim 3: To identify behavioural mediators of sustained weight loss in a previous male-only weight loss study In a secondary analysis of data from the SHED-IT Weight Loss Community Trial, an intention-to-treat, multiple-mediator model revealed the significant effect of the SHEDIT Weight Loss Program on weight at 6 months was mediated by increases in physical activity (steps/day) and decreases in take-away meals (kilojoules/day) and portion size at 3 months. The largest mediation effect was for physical activity (-0.6 kg; 95% CI - 1.4,-0.1). Overall, the mediators accounted for 47% of the intervention’s effect on weight.Secondary Aim 4: To examine the utility of SCT as a theoretical framework to explain the physical activity changes of men during weight loss Using data from Phase I of the SHED-IT Weight Loss Maintenance Trial, this study examined the utility of SCT to explain the physical activity changes of 204 men during weight loss. A longitudinal structural equation model revealed that SCT explained 61% of the variance in physical activity. All hypothesised pathways from cognitions to behaviour were supported with significant effects, except for the direct effect from outcome expectations. The strongest effects on physical activity were observed through changes in self-efficacy and intention. Secondary Aim 5: To evaluate the effect of the SHED-IT Weight Loss Maintenance Program on men’s weight and other health outcomes, 12 months after successfully completing the SHED-IT Weight Loss Program In a two-phase, parallel-group, assessor-blinded, RCT, 92 overweight/obese men, who had lost at least 4kg following the 3-month SHED-IT Weight Loss Program (Phase I), were randomised (Phase II) to either the (i) SHED-IT Weight Loss Maintenance Program or (ii) a self-directed control group, who received no additional resources. The 6-month SHED-IT Weight Loss Maintenance Program included written materials (handbook, logbook), bi-weekly text messages, emails (including video messages) and resources (website, pedometer, gymstick). Following Phase I, mean (SD) weight loss was 7.3 (2.5) kg (range 4.1-18.3 kg). At 12 months, the intervention group had regained 0.6 kg (95% CI -0.9. 2.2) (8% of Phase I weight loss) and the control group had regained 2.1 kg (95% CI 0.5, 3.7) (28% of Phase I weight loss), with no significant difference between groups (-1.5 kg, 95% CI, -3.7, 0.7, p=0.19). Significant treatment effects were found for fruit and vegetable intake (serves/day) and frequency of breakfast consumption at 12-months. While no betweengroup effect was found for weight, both groups demonstrated comparable maintenance to other, far more intensive, weight loss maintenance programs in the literature.Primary Aim: The primary aim of this thesis was to evaluate the effects of the SHED-IT Weight Loss Maintenance Program on men’s MVPA cognitions and MVPA behaviour, 12 months after successfully completing the SHED-IT Weight Loss Program Using data from the SHED-IT Weight Loss Maintenance RCT, the primary aim of this thesis investigated whether men randomised to receive the SHED-IT Weight Loss Maintenance Program reported greater improvements in MVPA cognitions and MVPA behaviour in the 12 months after initial weight loss, compared to men who did not receive any maintenance-specific advice. Although significant improvements were noted for most SCT cognitions and for MVPA behaviour during Phase I, no significant differences were observed between the groups during the weight loss maintenance RCT (Phase II). However, as observed for weight, initial improvements in behaviours and cognitions were largely maintained by both groups at the end of the study. Discussion: To date, men have been greatly under-represented in weight control and physical activity research. As such, there is a lack of knowledge concerning which theoretical and behavioural factors are most important to target in programs for men. This thesis determined that Bandura’s SCT provides a useful framework to understand the physical activity behaviour of men, particularly during weight loss. In addition, the thesis revealed that a male-only approach may be an effective way to engage men in weight loss efforts. Although the primary hypothesis of this thesis was not supported, men who received the SCT-based SHED-IT Weight Loss Program reported significant increases in MVPA and clinically meaningful reductions in weight, which were largely maintained at 12 months in both RCT study arms. Additional research studies with longer durations and adequate power for behavioural outcomes are needed to build on the current findings with additional insights into the utility of targeting theoretical constructs for physical activity during weight loss maintenance in men