Effects of mindful eating training on delay and probability discounting for food and money in obese and healthy-weight individuals
Introduction
Obese individuals are at greater risk for physical (e.g., type 2 diabetes; Field, Barnoya & Colditz, 2002) and mental health problems (e.g., depression; Sarwer & Thompson, 2002) compared to individuals of normal weight. According to the Centers for Disease Control and Prevention (CDCP; 2012), the prevalence of obesity has increased substantially in the last 30 years and is expected to continue to rise. Currently, over 35% of U.S. adults and 17% of U.S. children are obese. The increased prevalence of obesity across time has been attributed to a number of variables, including an increase in food consumption (Thompson et al., 2004).
Some researchers suggest that mindless eating is relevant to increases in food intake across the last several decades (e.g., Wansink, 2006). Mindless eating occurs when the act of eating is not consciously attended to; the cessation of eating is based on salient external environmental food cues (e.g., the bottom of a food bowl or the end of a television program) rather than internal cues that signal satiety. Other “mindless” environmental cues influence eating, such as larger food container sizes (Wansink & Kim, 2005), a greater number of people present during the meal (de Castro & Brewer, 1992), dimmed lighting (Wansink, 2004), and watching a longer television program while eating (Tuomisto, Tuomisto, Hetherington, & Lappalainen, 1998). Taken together, these factors may contribute to weight gain across time.
Within the past decade, there has been an increase in research and therapy-based interest in mindfulness, a term defined as “paying attention in a particular way: on purpose, in the present moment, and non-judgmentally” (Kabat-Zinn, 1994, p. 4). Within the mindfulness training model of acceptance-based treatments (e.g., Acceptance and Commitment Therapy; ACT), individuals learn to examine their behavior in an objective manner. Specifically, different phenomena that come into the individual's awareness (e.g., thoughts regarding past events) during the training session are observed but not evaluated (Marlatt & Kristeller, 1999).
Some studies have reported on the applicability of mindfulness to obesity. For example, mindfulness, compared to a control condition, has been shown to reduce food cravings in overweight and obese populations (Alberts, Mulkens, Smeets, & Thewissen, 2010). Other studies using ACT have improved the quality of life of obese individuals by reducing obesity-related stigma, psychological distress, body mass, and increasing physical activity (Lillis, Hayes, Bunting, & Masuda, 2009; Tapper et al., 2009). In one case study, mindfulness strategies were used to manage rapid eating, facilitate labeling of hunger, and eventually reduced the body mass of a morbidly obese individual by over 140 pounds (Singh et al., 2008).
While these studies made important contributions to improve the lives of obese individuals, the utility of mindfulness in the context of making food decisions has not been explored experimentally. One way to address this would be to train an individual to eat slowly while being non-judgmentally attentive to the sensations of tasting, chewing, and swallowing food (Zettle, 2007). This is intended to slow the pace of eating, increase time between bites of food, and increase awareness of the amount, quality, and quantity of the food that is eaten, which ultimately may lead to a reduction in food intake (Andrade, Greene, & Melanson, 2008; Scisco, Muth, Dong, & Hoover, 2011). Creating a context in which deliberate and thoughtful attention is placed on the act of eating may also reduce impulsive choice for food.
Impulsive choice patterns may be a behavioral mechanism relevant to obesity (e.g., Davis, Levitan, Smith, Tweed, & Curtis, 2006). Several self-report studies have shown that a positive relation exists between BMI and impulsive choice – a pattern of preference for smaller, immediate rewards over larger, later rewards (Borghans & Golsteyn, 2006; Komlos, Smith, & Bogin, 2004; Smith, Bogin, & Bishai, 2005; Zhang & Rashad, 2008). However, self-report measures can be sensitive to demand characteristics (e.g., experimenter expectancy), and participants may not be aware of their own behavior. Behavioral measures, such as the delay discounting (DD) task, may reduce problems inherent to self-report measures by examining patterns of choice between a smaller reward delivered immediately (e.g., $100 now) and a larger reward delivered after a delay (e.g., $1000 in one year). After the participant makes an initial choice, the immediate amount is increased or decreased until the participant switches to the immediate, smaller amount of the reward. The value at which the participant switches is called the indifference point. The process is repeated for a range of delays and indifference points are plotted for each delay value. In general, as the delay increases, the indifference points decrease in a hyperbolic manner (Mazur, 1987).
Research with humans has established that food is more reinforcing and tends to be more steeply discounted than a variety of other outcomes (e.g., money, books, music; Charlton & Fantino, 2008; Odum, Baumann, & Rimington, 2006). Therefore, it is possible to consider environmental conditions that capitalize on the immediacy of food delivery as a condition that would enhance excessive eating. Individuals who prefer more immediate, less healthy food options may be more susceptible to weight gain and later obesity (e.g., Maddock, 2004). Several studies have reported steeper discounting in obese populations compared to healthy-weight individuals for food (Rasmussen, Lawyer, & Reilly, 2010) and monetary rewards (Fields, Sabet, Peal, & Reynolds, 2011; Weller, Cook, Avsar, & Cox, 2008). Another study shows that when obese and overweight women dine out, those who tend to discount money more steeply (i.e., behave more impulsively) tend to consume more calories than those with lower discounting values (Appelhans et al., 2012). Moreover, overweight children who more steeply discount future monetary rewards are also less sensitive to weight-loss treatments when compared to less impulsive children (Best et al., 2012). This trend in the literature, then, may suggest that the degree to which one discounts future rewards may be a behavioral process involved in obesity.
The way in which we conceptualize impulsive behavior toward food-related outcomes and its relationship with body weight has important implications for weight management and obesity treatment. Research suggests that there are behaviors (e.g., physical activity, caloric intake), that tend to increase and maintain weight loss when modified (Anton et al., 2009). Acceptance-based strategies promote the willingness of an individual to experience what cannot be controlled (e.g., stress) and support behavioral choices that are based on non-judgmental awareness in the present moment (Zettle, 2007). One component of this, which may be relevant to food-related behavior via decreasing impulsivity, is mindful eating.
The present study tested the extent to which mindfulness training would affect impulsive choice patterns for food and money in an experimental setting. In Experiment 1, we attempted to systematically replicate a study by Rasmussen et al. (2010), which reported that individuals with high percent body fat (PBF) exhibited steeper discounting patterns for hypothetical bites of food, but not money. Consistent with Rasmussen et al., the present study used smaller values of outcomes (e.g., bites of food) across smaller windows of time (hours) to reflect the everyday food-related decisions that people make across a one-day time period. We improved on limitations of the initial study by controlling for estimated intelligence (IQ) and ensuring participants had no consumption of liquid or food at least 2 h prior to body fat measurements. In Experiment 2, participants were randomly assigned to one of two conditions to examine the extent to which a 50-min mindfulness-based workshop, using eating behavior as the focus, would change discounting patterns compared to a control condition. It was hypothesized for Experiment 1 that obese individuals would exhibit higher measures of impulsive choice for food compared to healthy-weight individuals, and small-value money would be less steeply discounted than food across participants. In Experiment 2, we hypothesized that participants who completed the mindful eating workshop would behave less impulsively with decisions regarding food and money compared to their pre-treatment measurements and that those in the control group would not change.
Section snippets
Participants
A total of 304 undergraduate psychology students (n = 211 female) from Idaho State University were recruited for participation in the study and received course credit as compensation for their time. The average age of the participants was 24.58 (SD = 7.68) years; 81.9% reported European-American ethnicity. The researchers asked participants to not eat or drink at least two hours before the experimental session.
Demographics questionnaire
The demographics questionnaire asked questions related to basic demographic
Participants
One hundred two randomly selected participants (n = 73 female) from Experiment 1 participated in the second experiment by returning to the laboratory within 21 days of their first session. The average interval between Session 1 and Session 2 was nine days. Each received course credit as compensation for their time. The average age of the participants was 25.46 (SD = 8.59) years; 80.4% reported European–American ethnicity. All participants were asked to not eat or drink at least two hours before
General discussion
The current study extended and replicated previous research by showing that percent body fat (PBF) predicted discounting patterns for hypothetical food, but not lower-value (i.e., $1 to $10) money. It also made a novel contribution to obesity and discounting literatures by demonstrating that with mindfulness training, discounting patterns could be changed at least momentarily for food, but not money, across individuals of various body fat percentages.
The current study contains limitations that
Acknowledgments
This study was conducted as the first author's Master's thesis at Idaho State University's Clinical Psychology doctoral program. We would like to thank Dr. Steven Lawyer for providing helpful information on discounting procedures and analyses, as well as feedback on an earlier draft of this manuscript. We would also like to thank Megan Brinton, Aarica Burke, Tiffany Doherty, Bradley Gossett, and Jennifer Stoll for their valuable assistance in collecting data for this study.
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