Predictors of weight loss success. Exercise vs. dietary self-efficacy and treatment attendance

Abstract

Pre-treatment diet and exercise self-efficacies can predict weight loss success. Changes in diet self-efficacy across treatment appear to be even stronger predictors than baseline levels, but research on changes in exercise self-efficacy is lacking. Using data from a pilot study evaluating tangible reinforcement for weight loss (N = 30), we examined the impact of changes in diet and exercise self-efficacy on outcomes. Multiple regression analyses indicated that treatment attendance and changes in exercise self-efficacy during treatment were the strongest predictors of weight loss. Developing weight loss programs that foster the development of exercise self-efficacy may enhance participants’ success.

Introduction

Recent statistics indicate that a third of Americans are obese and approximately another third are overweight (Flegal, Carroll, Ogden, & Curtin, 2010). Excess body weight increases risk for medical and psychiatric conditions, including type 2 diabetes, cardiovascular disease, osteoarthritis, some cancers, and mood, anxiety, and personality disorders (Barry et al., 2008, Flegal et al., 2005, Nguyen et al., 2010, Petry et al., 2008). Losing weight, even as little as 5% of body weight, leads to significant reductions in health risks (Institute of Medicine, 1995; National Heart, Lung, & Blood Institute (NHLBI), 1998; Powell, Calvin, & Calvin, 2007). Although weight loss programs based on reducing dietary intake and increasing physical activity can be effective in promoting weight loss, results are usually modest, and attrition from weight loss programs is high (e.g., Honas, Early, Frederickson, & O’Brien, 2003). Identifying patient characteristics and behaviors associated with successful weight loss could inform the development of more effective interventions to address the growing obesity crisis (Fontaine & Cheskin, 1997).

The concept of self-efficacy is fundamental to behavior change interventions based on social cognitive theory. Self-efficacy refers to individuals’ beliefs regarding their ability and competence to make the behavior changes required to achieve goals such as weight loss (Strecher, DeVellis, Becker, & Rosenstock, 1986). Individuals start pursuing goals with varying levels of self-efficacy, and higher self-efficacy is generally associated with greater effort and commitment to adopting healthy behaviors (Schwarzer, 1992). In turn, successful pursuit of goals can enhance self-efficacy (Batsis et al., 2009, McAuley and Blissmer, 2000, Strecher et al., 1986), increasing the likelihood behavior change will be maintained. Behaviors required for successful weight loss include reduction of caloric intake and increase in caloric expenditure, although the relationship between self-efficacy for these behaviors and successful weight loss is unclear.

Regarding pre-treatment diet self-efficacy, Prochaska, Norcross, Fowler, Follick, and Abrams (1992) found that pre-treatment scores on a measure of diet self-efficacy, the Weight Efficacy Lifestyle Questionnaire (WEL; Clark, Abrams, Niaura, Eaton, & Rossi, 1991), predicted weight loss among participants in a worksite weight loss program, but accounted for a very small proportion of the variance. Conversely, in a study of African American women receiving weight loss treatment from primary care physicians, pre-treatment WEL scores were actually associated with less weight loss, suggesting that self-efficacy beliefs can sometimes be inaccurate and arise from underestimating the difficulty of losing weight (Martin, Dutton, & Brantley, 2004). Fontaine and Cheskin (1997) found no association between pre-treatment WEL scores and either weight loss or program attendance in a sample of outpatients treated at a hospital based weight management program.

Some literature suggests that change in self-efficacy may be a more significant predictor of weight loss success than baseline self-efficacy. For example, while Martin et al. (2004) found that greater pre-treatment diet self-efficacy predicted less weight loss, they also observed that larger improvements in self-efficacy during treatment were associated with greater weight loss. Several other studies have also found that increases in diet self-efficacy scores from pre- to post-treatment are associated with greater weight loss (e.g., Bas and Donmez, 2009, Warziski et al., 2008).

Exercise is another crucial component of successful weight loss programs. In one study, Linde, Rothman, Baldwin, and Jeffery (2006) examined both the WEL and an exercise self-efficacy scale adapted from the WEL as predictors of weight loss at various stages in treatment. They found pre-treatment scores on both the WEL and the exercise self-efficacy scale were associated with behaviors required for weight loss and with weight loss during treatment. However, they did not assess whether changes in exercise self-efficacy from pre- to post-treatment predicted greater weight loss.

Poor attendance and attrition from treatment are among the biggest barriers to the success of behavioral weight loss interventions (Gardner et al., 2007, Honas et al., 2003, Teixeira et al., 2004), and better session attendance is associated with greater weight loss during treatment and better maintenance of weight loss after treatment (Chao et al., 2000). The ability to persevere in treatment may be related to self-efficacy. For example, Bernier and Avard (1986) found that participants who completed treatment had higher pre-treatment self-efficacy than those who dropped out prematurely.

The goal of the current study was to evaluate the effects of pre-treatment self-efficacy for diet and exercise, as well as changes in self-efficacy occurring during treatment, on weight loss success. Finding an effect of baseline self-efficacy could improve understanding of individual differences in the likelihood of experiencing success in a behavioral weight loss intervention, while strong effects of changes in self-efficacy would argue for including techniques for improving self-efficacy in behavioral weight loss programs. Given the mixed findings regarding associations between dietary self-efficacy and weight loss and the relative paucity of studies examining associations between exercise self-efficacy and weight loss, examining the contribution of both forms of self-efficacy should shed light on their relative importance to weight loss success. Because practicing the behavior changes recommended by behavioral weight loss programs could contribute to both weight loss and to changes in self-efficacy, treatment attendance and changes in caloric intake and physical activity level were included in the analysis.