The association between body weight, value of the future and dietary behavior

Kim Garza reports on preliminary results of a cross-sectional survey of Auburn University students and employees

People who are overweight insist they want to lose pounds, but they often fail to limit food intake or get the necessary exercise. Numerous factors affect their decision not to do what they need to do, which seems irrational. That conundrum led Dr. Kim Garza to ask whether people who are overweight or obese value the future differently from people who are a healthy weight, and ask how this difference might be related to dietary behaviors.

Behavioral economics is the study of human behavior and how it is affected by certain cognitive biases in decision-making. A concept in behavioral economics known as “delay discounting” is related to the value people place on the future. Garza’s research applies behavioral economic theory, including the concept of delay discounting, to the study of preventive health behaviors, including medication adherence, diet and physical activity.

Body mass index retro poster.
Body mass index retro poster.

Garza, an assistant professor in the Auburn University School of Pharmacy, sought an answer to her questions by surveying 514 students and 478 Auburn University employees about their eating habits. The online survey included questions about subjects such as eating food away from home, buying convenience foods, grocery shopping and label reading.

DELAY DISCOUNTING: Delay discounting refers to the human propensity for choosing immediate benefits over delayed benefits, even when the delayed benefit is greater. For example, ask a friend if they want fruit (the healthy option) or chocolate cake (the tasty option) right now, and they’re likely to say chocolate cake. But they will insist they want fruit next week. The future benefit of the fruit might be greater than the present benefit of the chocolate cake, but people tend to devalue benefits in the future.

Garza sought to untangle the association between weight, degree of delay discounting and dietary behaviors. She wanted to determine whether there is a differential association between behavior and delay discounting in people who are overweight or obese compared to people who are underweight or maintaining a healthy weight.

NOW, OR IN THE FUTURE: As noted, delay discounting refers to the decline in perceived value of something between the present time and some time in the future. To determine delay discounting, survey participants were asked, “Imagine that you have a choice between two dollar amounts: one you would receive now and one you would receive one day from now. Would you prefer $500 now or $1,000 one day from now?”

They were asked a similar question several times, with the delay increased to one week, one month, six months, one year, five years and 25 years. Their responses were used to calculate the “area under the delay discounting curve.”

“Area under the curve (AUC)” is a mathematical term used as a measure of discounting, referring to the actual area under the delay discounting curve plotted on a graph. The higher the AUC, the lower the degree of delay discounting (and the higher the value placed on the future).

Of the student survey respondents, 35 percent were overweight or obese, as determined by their BMI. Of the employees, 57 percent were overweight or obese.

For both students and employees, the AUC was lower for overweight and obese participants (meaning a lower value of the future) compared to underweight or healthy weight participants. Garza also found that the mean AUC of employees was significantly lower than that for students.

“These findings suggest that people who are overweight or obese may place a greater value on the immediate benefits of a poor diet (such as convenience and taste) compared to the benefits of eating a healthy diet, which may not happen until far in the future,” Garza says. “We’ve seen this in previous studies. We have since looked at other associations in our data and found some interesting results, to be published in an upcoming article.”

Garza’s research was funded by the Auburn University Internal Grants Program. In the future, she says she plans to use survey responses to look at correlations between AUC and dietary behaviors in people who are overweight/obese compared to those who are underweight/healthy weight, as well as look more closely at the BMI and dietary behaviors of people in the high and low AUC groups.