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Weighing the Options: Criteria for Evaluating Weight-Management Programs
In addition to the limitation of using a database for a unique and poorly defined subset of the population, our understanding to date of successful weight management is further limited by its being based on studies in which the treatment approaches may have been less than ideal (e.g., separating weight management into discrete phases of weight loss and maintenance) and in which the outcomes used to evaluate success may not have been appropriate (e.g., reaching an ideal weight).
Predictors of successful weight management may differ in future studies that use different weight-management approaches, in particular, the components of the broader definition of success recommended toward the end of this chapter. The following review is limited by the existing literature, which has used the more narrow definition of success at weight management—simple weight loss.
PREDICTORS OF WEIGHT LOSS
Factors that predict weight loss are shown in Table 7-1; these include personal, process, and treatment factors. Personal and process factors pertain to an individual; treatment factors pertain to a program.
Personal factors include initial weight or body mass index (BMI) and resting metabolic rate or resting energy expenditure (REE). The greater the initial BMI, the greater the initial weight loss. Additionally, although REE is most directly related to lean body mass, total weight affects REE as do age, gender, and height. Those with higher REE have higher energy requirements, facilitating more weight loss proportionate to intake. Adipose hypercellularity, usually associated with excessive deposition of fat cells in childhood, has been associated with greater weight loss. However, when the lower limit of adipose cell size is reached, further weight loss is difficult, often leaving the person still obese. Another problem is that the smaller fat cells may produce more lipoprotein lipase, which may stimulate hunger and facilitate increased fat deposition (Kern et al., 1990). Because it is difficult to measure fat cell number, estimates of percentage of total body fat and body-fat distribution are more useful measures for assessing progress (Perri et al., 1992). Although body-fat distribution is not a clear predictor of weight loss, women with upper-body obesity may be more likely to improve their waist-to-hip ratio (WHR) with weight loss, while the WHR for women with lower-body obesity tends to remain constant with weight loss (Wadden et al., 1988).
Self-efficacy is a person's confidence in his or her ability to perform a given task or achieve a certain goal. Higher perceived self-efficacy in