The study was conducted at the Pennington Biomedical Research Center (PBRC), Baton Rouge, LA, USA. All applicable institutional and government regulations concerning the ethical use of human volunteers were followed. All participants provided written informed consent and the research was approved by the Institutional Review Board of the PBRC.
Fifty-one healthy males and females, ages 18 to 54 years with body mass index 20 to 35 kg/m2, inclusive, were enrolled in the study. Exclusion criteria were: 1) use of medications that affect eating behavior or body weight (e.g., antipsychotic medication); 2) diagnosis of a chronic disease such as diabetes, cardiovascular disease or cancer; 3) tobacco use; 4) refusal to eat the foods provided during the study; and, for females, 5) irregular menstrual cycles or pregnancy. Three participants failed to complete the study due to scheduling difficulties. Participants received monetary compensation ($125 USD) for participation.
Study Design and Random Assignment
Using a within subjects or repeated measures design, participants completed four conditions in random order. During all conditions, participants were provided with a meal consisting of 16 food items served simultaneously in individual dishes that included grilled and breaded chicken and other low- and high-fat food items. Water and fruit punch were also served with each meal. The types and amount of foods served during the test meals are outlined in . The four conditions follow.
Serving size and energy (kcal) and macronutrient content of foods served during the study.
- Control: participants were not allowed to read or watch TV while eating.
- Reading: participants were asked to read provided material while eating.
- TV-ads: participants viewed a TV program that was interspersed with an equal number of food and non-food ads while eating.
- TV-no ads: participants viewed a TV program without ads while eating.
Participants completed two days of testing, consuming a standard 359 kcal breakfast followed by the first test meal at lunch (4 hours after breakfast) and the second test meal at dinner (4.5 hours after lunch). The food items and energy content of the breakfast, lunch, and dinner meals are provided in . On the second test day, the same standardized breakfast was consumed, followed by the third test meal at lunch and the fourth test meal at dinner. Test days were scheduled 7 ± 2 days apart. To reduce demand characteristics, participants were told that the purpose of the study was to test the consistency of taste rating over time. Energy intake was quantified by weighing each food item before serving it to participants and after participants ate. Each food was measured to 0.1 grams and the food was weighed out of sight of the participant.
Sample Size Determination (Statistical Power Analysis)
The study relied on a within-subjects design; as such, each participant served as his/her own control and all participants completed all four conditions. The sample size was determined by an a priori power analysis that relied on the published literature to estimate the minimally acceptable effect size (10.75% increase in energy intake). Variance estimates for energy intake were calculated based on previously collected laboratory data that were derived from similar test meals. The power analysis assumed a large standard deviation (SD) for energy intake (465 kcal), 80% power, an effect size of 10.75%, alpha = 0.05, and a one-sided hypothesis test. Given these assumptions, the results of the power analysis indicated that we could detect a 10.75% increase in energy intake with 48 participants. This power estimate was considered conservative based on the large variance and inclusion of an effect size that is smaller than any effect size reported in the literature to date.
Television Program, Advertisements, and Reading Material
During the TV conditions, participants viewed two different episodes of the same program (Net Cafe
). This program describes the uses of the internet for security technology, arts, and entertainment, including the performing arts. The Net Café program was broadcast in over 100 countries. The production style and episode templates were consistent between the two episodes, with both focusing on interviews and demonstrations with four to five technology developers and community members. One episode contained ads and one did not. The ads consisted of six food ads (e.g., a pizza commercial) and six non-food ads (e.g., an automobile commercial) that lasted 30 seconds each and were recorded in the weeks prior to the study (the ads are listed in ). Hence, ads that were in circulation at the time of the study were utilized. The six food and non-food ads were selected randomly by recording network television for 3 hours in the evening and selecting the first six food and non-food ads.
List of the food and non-food advertisements shown in the TV-ads condition.
Participants were informed that they would be asked several questions about the material that they viewed or read during the TV and reading conditions. This procedure ensured that participants watched the TV programs and read the narrative, i.e., attended to and dedicated cognitive resources to these stimuli while eating.
Test of Memory for Ads
Following the TV-ads condition, participants' memory for the ads from the TV program was quantified using methods similar to those of Halford (15
). The memory task consisted of a list that contained descriptions of ads that were and were not in the TV program. As outlined in , 50% of the ads on the list were in the program and 50% were not. Participants were asked if they remembered each ad as being in the program. Ad memory was quantified by calculating the proportion of ads that participants remembered. Participants' familiarity with the ads was also quantified using similar methods, but this variable is not described in further detail because it was not of primary interest and did not correlate with the primary outcome variables, including energy intake. Ad memory data were fitted to a dichotomous Rasch model (17
) to assess the reliability and construct validity of the ad recognition task and to test for differential item functioning (DIF) between males and females. Instrument reliability was acceptable, and DIF was not detected, indicating that item responses were not gender-biased. Average model fit was acceptable, although significant item-item interactions were identified at the level of individual respondents. In practice, such interactions equate with nonlinearities that threaten the validity of the person score. These effects were removed using the model error components, generating adjusted person scores that were then incorporated into all subsequent analyses.
Self-report measures and measures of distractibility and reading level
The following assessments were completed during baseline.
Conner's Continuous Performance Test –II (CPT-II)
The CPT-II is a norm-referenced computer-based test that measures an individual's ability to attend to and concentrate on prompts of visual stimuli. The CPT-II provides an objective measure of attention deficit/hyperactivity disorder (ADHD) symptoms and it has established reliability and validity (18
). The Confidence Index was used as an objective measure of distractibility, quantifying the extent to which a participant's responses reflect the performance of an ADHD population. Inattentiveness or the tendency to be easily distracted is a core feature of ADHD, and the majority of people (at least children and adolescents) diagnosed with ADHD exhibit this symptom (20
Wide Range Achievement Test 4 (WRAT-4)
Participants completed the WRAT-4, a norm-referenced measure of academic skills, to obtain an objective measure of reading level and to determine if the reading material utilized in the study was consistent with participants' reading level. Grade equivalents and standard scores are obtained with the WRAT-4.
The Eating Inventory is a 51-item self-report inventory that assesses dietary restraint (the intent to restrict energy intake), disinhibition (the tendency to overeat), and perceived hunger. The Eating Inventory has been found to be reliable and valid (21
). In this study, the Eating Inventory was used to quantify dietary restraint, which is associated with body weight and energy intake (22
), and the relation between energy intake and emotional arousal induced by movie watching (10
Visual Analog Scales (VAS)
Computerized VAS were completed before and after each test meal to measure subjective ratings of hunger, fullness, desire to eat, food craving, strength of cravings, and desire to eat something sweet, salty, and fatty. When completing the VAS, participants rated the intensity of these subjective states on a 100-unit line anchored from “not at all” to “extremely.” VAS have been found to have satisfactory reliability and validity (24
Visual Analog Mood Scales (VAMS)
Computerized VAMS were used to measure mood (happy vs. sad), alertness (alert vs. drowsy), tranquility (troubled vs. tranquil), anxiety (tense vs. relaxed), energy levels (lethargic vs. energetic), and calmness (calm vs. excited) before and after each test meal to determine if the TV programs or the reading material differentially affected mood. VAMS rely on the same 100-unit line as the VAS ratings and have been found to have satisfactory reliability and validity (25
Prior to reporting to the clinic to eat breakfast on test days, participants were instructed to fast for 12 hours, refrain from vigorous exercise for 24 hours, and refrain from consuming alcohol for 48 hours. Upon arrival they completed a questionnaire to assess if they had fasted or were experiencing a cold or allergies. Participants reporting cold or allergy symptoms that affected their ability to taste or smell food were rescheduled. Female participants completed all tests meals during the luteal menstrual cycle phase.
At each test meal, participants were instructed to eat as much or as little as they wished. The length of time that participants remained in the room (32 minutes) was standardized across testing conditions. For the purpose of the study, an office at the PBRC was altered to accommodate the television and to provide a comfortable environment in which to eat. Book shelves and office equipment were removed or covered. Environmental stimuli in the room were identical across conditions (e.g., the TV was always in the room, but it was only on during the two TV conditions). Participants completed VAS and VAMS ratings before and after each test meal. Upon completion of the TV-ads condition, participants completed the memory task. Participants answered questions about the reading material after the reading condition.
Data Analytic Plan
The primary outcome variables were energy intake (kcal) and intake of kcal from fat, carbohydrate, and protein. Repeated measures analysis of variance (ANOVA) was used to test if energy intake differed significantly by condition (control, reading, TV-ads, TV-no ads). Sex was a between subjects factor.
Correlation analyses were used to examine the association of distractibility with energy intake and body weight, including sex as a partial covariate. Correlation analyses were also used to assess the relationship between memory for ads and energy intake and body weight. The distributions for ad memory were negatively skewed; therefore, non-parametric Spearman's rho correlation coefficients were reported for these variables. Memory for ads was measured during the TV-ads condition, but was correlated with energy intake in all conditions to determine if people with better memory for ads have greater energy intake in general, or if the associations only occur when certain stimuli, namely TV, are present.
The alpha level for the aforementioned primary outcome variables was 0.05. The number of correlations was limited to only those of primary interest and was planned a priori; therefore, alpha was set at 0.05 for the correlation analyses.
Repeated measures ANOVAs were used to test if change in subjective ratings of appetite and mood differed across conditions. Change scores (post-meal minus pre-meal) were calculated for the VAS and VAMS ratings. These change scores were subjected to repeated ANOVAs, which included condition (meal type) as the repeated factor and sex as a between subjects factor. Alpha was set at 0.01 for the VAS and VAMS analyses to help control alpha inflation.
To ensure data integrity, the presence of order effects was tested with repeated measures ANOVA, with contrasts to test for energy intake differences among the first, second, third, and fourth meal presented during the study. These tests were conducted with the variable of primary interest, energy intake.
The ANOVAs reported herein relied on the Greenhouse-Geisser p-value. All analyses were conducted with SPSS, Version 15, Software (Chicago, IL), with the exception of the Rasch model analysis, which were conducted using Winsteps, Version 3.65.1(Chicago, IL).