2.1 Study overview
A three-group repeated-measures experimental study was conducted to determine whether providing information about calories and exercise equivalents at the point-of-choice for a fast food meal would decrease calories ordered or consumed among overweight and obese 18-34-year-old women at a public university in southern Florida in 2009, and to investigate any correlation with consumption with prior dieting history, qualified as dietary restraint in this study. All participants were asked to participate in two sessions during a two-week period. The Florida International University Institutional Review Board approved this study. All persons gave their informed consent prior to inclusion in the study.
2.2 Study participants
A total of 62 overweight or obese female participants were recruited on a south Florida college campus. Telephone and in-person screening determined whether participants met the inclusion criteria: female, age 18-34 years old, BMI at least 25 and less than 40, as calculated from researcher-measured height and weight, ate fast food at least “occasionally”, and able to read and speak English. Participants were also screened at this time for dietary restraint for randomization into the three study groups. Persons were excluded for dieting in the last three months; requiring a special diet such as vegetarian, kosher, or accommodating a food allergy or health condition; being pregnant or giving birth in last year; having a chronic disease such as heart disease or diabetes; having current self-reported depression, self-reported alcohol or drug abuse, or eating disorder; being a health major; not typically eating lunch; and participating in a previous food-related study. Exclusion criteria were set to ensure participants were healthy and able to partake in a food-related study and to help avoid any bias gained from previous food-related studies. In order to help further blind participants to the menu manipulation aspect of the study, participants were told that the purpose of the study was to “better understand fast food meal choices”.
2.3 Experimental design
Participants attended two meal sessions, Lunch 1 and one week later Lunch 2. The food choices were from a fast food restaurant located on the university campus. The restaurant is part of a national chain specializing in hamburgers and French fries. The foods were in their original portion-controlled wrappers or packaging, which allowed the researcher to easily record choices made by participants. The study took place in a controlled setting within the university, at a private conference room in the University’s Graham Center nearby the student union where the students normally eat. Incentives for the participants included $5 for completion of the screening questions, the two free lunches, and a $20 gift card at each lunch.
At the start of each Lunch, participants were given a menu. The paper menus were in a similar format to menu boards at fast food restaurants. The food items were those available for lunch at Burger King on the dates of the experiment. The participants were able to choose entrées (e.g. Hamburger, Whopper, TenderGrill, BK Veggie Burger or TenderGrill), a garden salad, side dishes (i.e., fries, onion rings), condiments (ketchup, mayonnaise, fat free ranch dressing, or honey mustard dressing) and a drink (i.e., water, Coca-Cola, diet Coca-Cola, or apple juice). The observer recorded the quantity of the food ordered and eaten by using a digital food scale, weighing the remaining portions and using a measuring cup for the liquids. The researcher ensured that all participants had finished eating and had left the study site prior to weighing and measuring left-over foods and drinks. Calories consumed were derived by taking food waste and weighing on a digital scale and calculating total calories eaten by the following formula: Total Calories For Food Item Chosen–Food Waste = Calories Consumed.
Lunches were served from 11:30 a.m. until 3:00 p.m., and participants made appointments at 30-minute increments. All participants were told in advance that they would not be able to leave the study site with any leftover food, to limit the possibility that participants would order more food than they intended to consume. During Lunch 1, participants were given a menu, similar in format to menu boards at fast food restaurants. Participants were able to order any foods and beverages from the menu, which listed only names of items, no calories or exercise equivalents.
The experimental manipulation took place one week later at Lunch 2. All participants were randomly assigned to one of three groups. Each group received different information on their menus: no information on calorie or exercise equivalents, calories only, or calories and exercise equivalents. Column headers for the exercise equivalents and calories described the numbers (“minutes to burn off food in walking”, “calories”), as did labels after each values. The exercise equivalence of calories was calculated based on an intensity level of 3.3 METs for walking at the moderate pace of 3.0 mph on a firm surface [16], and a body weight of 160 pounds.
2.4 Data collection
At the research table, participants completed standardized questions on the following demographic information: age, marital status, education, income, race, religion, and whether the participant was a smoker. Body Mass Index was assessed by the investigators at the research table using a standardized height and weight measurement procedure as outlined in Third National Health and Nutrition Examination Survey (NHANES III) Anthropometric Procedures Manual [15].
Dietary restraint was determined using the TFEQ [17]. Scores on the TFEQ restraint sub-scale range from 0 to 21, with restrained eaters defined as those who have a score of 13 or above. Participants were blocked by restraint in order to test whether unrestrained and restrained eaters responded differently, since restraint has been shown to influence food choice and the reading of nutrition labels [18],[19], and were then randomly assigned to one of three study groups.
2.5 Statistical analysis
ANOVA and chi-square tests were conducted to compare demographic information by study group. Both the foods ordered and the foods consumed were analyzed. Within each study group, a paired t-test was conducted to test for the change in calories ordered or consumed from Lunch 1 to Lunch 2. The subsequent change by study group was calculated as the mean (plus or minus the standard error) of the changes from Lunch 1 to Lunch 2 for each of the group’s individual members.
Proportionate change for calories order and calories consumption from Lunch 1 to Lunch 2 were calculated as the mean (plus or minus the standard error) of the proportionate changes of each of the group’s individual members. The t-tests were used to examine whether the proportionate changes are significant.
Analysis of covariance (ANCOVA) was conducted using General Linear Model in SPSS 17.0 statistical software (SPSS Inc., 2008) to test for differences between study groups in difference from Lunch 1 to Lunch 2 in calories ordered or consumed. The effect size (partial eta squared) and observed power (using alpha = 0.05) are also calculated using SPSS. Two general linear models were created, both controlling for age, BMI, and dietary restraint, and with study group as the fixed factor. For model 1, the response variable was the difference from Lunch 1 to Lunch 2 in total calories ordered, and an additional covariate was calories ordered in Lunch 1 (control meal). For model 2, the response variable was the difference from Lunch 1 to Lunch 2 in total calories consumed, and an additional covariate was calories consumed in Lunch 1. Both models assumed that the response variables were continuous, residuals were normally distributed, and the subjects were independent. Total number of items ordered was also compared by study group.