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Altering Portion Sizes and Eating Rate to Attenuate Gorging During a Fast Food Meal: Effects on Energy Intake

^a Division of Endocrinology, Department of Medicine
^b Clinical Research Program, Children's Hospital Boston, Boston, Massachusetts

	ABSTRACT

TOP ABSTRACT METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
OBJECTIVE. Eating large amounts of food at a rapid rate, defined as gorging, may contribute to excess energy intake. We aimed to evaluate whether altering portion sizes and eating rate could decrease energy intake during an extra-large fast food meal.

METHODS. Subjects were adolescents (n = 18), 13 to 17 years of age, who reported eating fast food 1 time per week. BMI exceeded the 80th percentile for all subjects. Three feeding conditions were evaluated with a crossover design. Total amounts and types of foods and beverage served during the meal were held constant across conditions, equaling 125% of that consumed during a baseline assessment visit when subjects were offered unlimited amounts. The meal (chicken nuggets, French fries, and cola) was presented as 1 large serving at a single time point (condition A, standard), portioned into 4 smaller servings presented at a single time point (condition B, effects of portioning), or portioned into 4 smaller servings presented at 15-minute intervals (condition C, effects of portioning and eating rate). Energy intake across conditions was compared by using analysis of variance.

RESULTS. Energy intake was not significantly different, whether expressed in kilojoules (mean ± SEM: condition A, 5552 ± 357 kJ; condition B, 5321 ± 433 kJ; condition C, 5762 ± 500 kJ) or relative to total daily energy expenditure (mean ± SEM: condition A, 51.9 ± 3.5%; condition B, 48.2 ± 4.0%; condition C, 53.0 ± 4.3%).

CONCLUSIONS. Adolescents consumed 50% of energy needs regardless of manipulations in portion sizes and eating rate to attenuate gorging. This finding suggests that nutritional factors inherent to fast food, such as low levels of dietary fiber, high palatability, high energy density, high fat content, high glycemic load, and high content of sugar in liquid form promote excess energy intake.

Key Words: adolescent obesity • eating behavior • energy intake • portion size

Abbreviations: NDSR—Nutrition Data System for Research

Fast food is ubiquitous, and frequent consumption may be among the high-impact dietary behaviors that contribute to excess weight gain in adolescents. An estimated 75% of adolescents eat fast food 1 times per week,¹ representing a dramatic increase since the 1970s.² Escalating portion sizes of menu items³ and increasing frequency of fast food meals² have paralleled the increasing prevalence of obesity.⁴ Parallel trends raise the possibility of a causal relationship between fast food consumption and the obesity epidemic. Moreover, several studies have shown a direct association between fast food consumption and body weight or energy intake.^5–7

Many characteristics of fast food meals have been shown to promote energy intake in feeding studies, including enormous portion sizes,^8,9 rapid eating rate,¹⁰ low levels of dietary fiber,¹¹ high palatability,¹² high energy density,¹³ high fat content,¹⁴ high glycemic load,¹⁵ and high content of sugar in liquid form.¹⁶ Of these, only 2, namely, enormous portion sizes and rapid eating rate, are not nutritional factors inherent to fast food. The verb "to gorge" means "to swallow in large mouthfuls or quantities" or "with greediness,"¹⁷ which describes consumption of enormous portion sizes at a rapid rate.

Strong evidence links portion sizes with energy intake.^8,9,18,19 Large portion sizes may override internal homeostatic mechanisms that regulate satiety, possibly by distorting visual cues and decreasing awareness of food consumption.^19,20 In a study using "bottomless bowls" to alter portion sizes inconspicuously, Wansink et al²⁰ concluded that individuals eat more when they are unable to monitor intake visually. Rolls et al¹⁹ came to a similar conclusion on the basis of a study showing increased energy intake with progressively larger portions of snacks provided in opaque packages.

The effects of large portion sizes on energy intake also may be attributable, in part, to a rapid eating rate.^8,10 Kral et al¹⁰ found a direct correlation between eating rate and meal size when obese adults were offered unlimited portions of a liquid test meal. Fisher et al⁸ attributed increased energy intake to accelerated eating rate, as indicated by an increase in bite size with no change in bite frequency, when young children were served relatively large versus age-appropriate portions of a lunch entrée. A rapid eating rate may not allow adequate time for development of physiologic satiety signals involved in meal termination, although data are inconsistent.^10,21–24

We showed previously that excess energy intake is a characteristic outcome when adolescents, particularly those who are overweight, are presented with an extra-large fast food meal.²⁵ Conceptually, an extra-large meal is a stimulus that fosters the behavioral response of gorging, with the outcome being excess energy intake. The purpose of this study was to determine whether reducing portion sizes and slowing eating rate, to attenuate gorging, would decrease energy intake during a fast food meal. This study differs from previous studies of portion sizes^8,9,18,19 in that we evaluated portioning (ie, dividing an extra-large meal into smaller fractions, without altering absolute amounts of foods and beverage), as opposed to portion control (ie, serving smaller absolute amounts). If visual cues enhance awareness of consumption and thereby curb energy intake, then simple measures involving portioning and packaging of fast food might prove useful, from a public health perspective, in preventing and treating adolescent obesity. If visual cues do not enhance awareness, then fundamental improvements in nutritional factors inherent to fast food, a prospect that has been historically challenging,²⁶ would seem to be warranted in efforts aimed at combating the obesity epidemic.

	METHODS

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Subjects
We enrolled 20 adolescents, 13 to 17 years of age, who reported eating fast food 1 time per week. Screening for inclusion and exclusion criteria was conducted through telephone interviews with the adolescent and a parent. Adolescents with BMI values exceeding gender- and age-specific 85th percentile values,²⁷ on the basis of self-reported weight and height data, were invited to participate in the study. Weight and height were measured at the initial visit to ensure that all enrolled subjects had BMI values exceeding the 80th percentile, allowing for some inaccuracy in self-reported data. We excluded adolescents who reported having a diagnosis of a major medical illness or eating disorder, smoking 1 cigarette in the past week, or taking any prescription medication that may affect food intake. During the telephone interviews, we collected demographic data, including gender, ethnicity and race, and date of birth.

The protocol was approved by the institutional review board at Children's Hospital Boston (trial registration NCT00121706 [see www.clinicaltrials.gov]). Newspaper advertisements and fliers, stating that the purpose of the study was to collect information on how teenagers eat fast food, were used to recruit subjects. At the time of recruitment, we confirmed that the subjects did not have aversions to menu items in the fast food meal served during study visits (ie, chicken nuggets, French fries, and cola). We did not mention strategies for altering portion sizes and eating rate. Written informed consent and assent were obtained from parents and subjects, respectively. Data were collected during the summer of 2005. As incentive, we offered each subject $150 in gift certificates, with $25 provided at each of 4 visits and an additional $50 provided after completion of 6 telephone-administered, 24-hour dietary and physical activity recall interviews.

Overview
The initial study visit was considered a baseline assessment visit for establishment of individualized amounts of foods and beverage that would be served during each of 3 subsequent test visits. We instructed subjects to eat a standard breakfast of cold cereal and milk at 9:00 AM on the day of each visit and then not to eat or to drink anything, except water, until after the visit. At 1:30 PM, we served a meal from a national fast food chain in the naturalistic setting of a food court. The length of each meal was 1 hour. Meals were served to groups of 3 subjects, on average, to foster socializing, which is characteristic of the fast food experience for adolescents. Boys and girls were in separate groups, to avoid any effects of social interactions between the genders that might influence eating behaviors.

Before each meal, we asked each subject to rate his or her level of hunger by using a 10-cm visual analog scale, anchored with the descriptors "not at all hungry" and "extremely hungry." After the meals, we asked each subject to rate the meal size, relative to the size of fast food meals that he or she consumed typically, by using a 10-cm visual analog scale ranging from "much smaller than usual" to "much larger than usual."

Weight and height were measured at each visit by using an electronic scale (model BWB-800; Tanita, Tokyo, Japan) and stadiometer (model PE-AIM-101; Perspective Enterprises, Portage, MI), respectively. We calculated BMI as weight in kilograms divided by the square of height in meters.

Baseline Assessment Visit
During visit 1, we evaluated energy intake in an extra-large meal containing conventional fast food (Table 1), by using methods modeled after our previous study.²⁵ The following standard instructions were read to the group of subjects before the meal: "We will bring each of you a meal. Eat as much or as little as you like, until you have had enough. There is more food available, and you may eat as much as you want. Please do not share your food with others in the group. If you need more of anything, just ask. Keep your packaging on your tray." Research staff members monitored food intake discreetly. Whenever approximately three fourths of the extra-large meal portion of chicken nuggets or fries had been consumed, a refill portion of the item was added to the tray (Table 1). Empty cola containers were replaced with full containers immediately. Ketchup and sweet and sour sauce could be obtained from the center of the table throughout the meal. By using this standardized protocol, we provided more of the items that each subject enjoyed most and would be likely to order in large portions when given the option.

Test Visits
By using a crossover design for visits 2 to 4, we assigned each subject randomly to 1 of 6 possible sequences of 3 feeding conditions. The random assignment was stratified according to gender. Identification numbers for male participants were matched randomly to a single block of 12 assignments (ie, with each possible feeding sequence represented twice) and those for female participants to 2 blocks of 12 and 6 assignments. The assignments were prepared on index cards by the study statistician and were delivered in opaque envelopes to the principal investigator, to be opened after each participant's baseline assessment visit.

Meal delivery varied according to condition, as described in Table 2, with the total amounts of foods and beverage held constant across conditions. In brief, the fast food meal was presented as 1 large serving at a single time point (condition A, standard), portioned into 4 smaller servings presented at a single time point (condition B, effects of portioning), or portioned into 4 smaller servings presented at 15-minute intervals (condition C, effects of portioning and eating rate). The total amount of each item other than condiments in the meal (ie, nuggets, fries, and cola), whether presented as a single large serving or portioned into 4 smaller servings, was equal to 125% of that consumed during the baseline assessment. We did not provide any refill portions during the test visits.

Energy intake, the primary study outcome, was calculated on the basis of the difference in weight between the amount of each menu item served and that remaining on the tray or in boxes at the end of the meal. All containers were weighed to the nearest 1 g on an electronic digital scale before and after the meal, and NDSR was used to convert the weight of each item consumed to energy intake, as described above.

Dietary and Physical Activity Recall Interviews
We collected dietary and physical activity data during telephone-administered, 24-hour recall interviews, by calling each subject on the 2 days after each of the 3 test visits to assess behaviors during the day of the visit and the day after the visit. The focus of this report is on data corresponding to the day of each visit, with particular attention directed toward recall of fast food consumed during the visit. The interviewer was masked with respect to the sequences of conditions.

Dietary intake was assessed with a multiple-pass method using NDSR. The interviewer prompted the subject to list in sequence the foods and beverages consumed during the previous day, to identify omissions in the initial list, and then to provide details (eg, portion sizes and brand names) concerning each reported item. Intake was reviewed and confirmed at the end of each interview. Recalled energy intake during the fast food meal at the food court provided a measure of awareness with regard to fast food consumption.

To assess physical activity, we asked the subject to recall the activity performed most during respective 15-minute time blocks throughout the preceding day (12:00 AM to 11:59 PM) and then to rate the relative intensity as light, moderate, hard, or very hard.²⁸ This protocol also provided information regarding inactivity (eg, sleeping or television viewing). A metabolic equivalent level was assigned to each activity for calculation of a physical activity factor. As points of reference, resting has a metabolic equivalent level of 1.0 and brisk walking has a level of 5.0.²⁹ Total energy expenditure was estimated by multiplying the basal metabolic rate, calculated with validated equations,³⁰ by the physical activity factor.

Before the interviews, we held in-person group training sessions on how to estimate food and beverage portion sizes and how to describe the intensity of physical activity. The training sessions occurred after the fast food meal during the baseline assessment visit. Subjects practiced recalling dietary intake and physical activity during the training sessions.

Statistical Methods
We hypothesized that energy intake would be higher when the fast food meal was presented as 1 large serving at a single time point (condition A), compared with multiple smaller servings at 15-minute intervals (condition C). In addition, we hypothesized that energy intake would be intermediate when the meal was presented as multiple servings at a single time point (condition B). To test this hypothesis, analyses were conducted by using SAS 9.0 statistical software (SAS Institute, Cary, NC).

We compared study outcomes across the 3 feeding conditions by using repeated-measures analysis of variance. All results are presented as mean ± SEM. Statistical significance was defined as P < .05. The analysis of variance included a fixed effect to test for systematic variation across the 3 successive visits (order effects) and an interaction term to test whether differences among feeding conditions depended on the position in the sequence (effect modification). To account for correlated outcomes within subject, we used a compound-symmetry covariance structure for the repeated-measures analysis, equivalent to a random subject effect in ordinary analysis of variance.

Power analysis for the 3-period crossover design was based on an estimate of intersubject variability in energy intake³¹ and a conservative estimate of 0.2 for intrasubject, interday correlation. The sample of 18 provided 80% power to detect a difference as small as 689 kJ between condition A and condition C, our primary comparison, with the specified statistical criterion (P < .05). For the 2 secondary comparisons (condition A versus condition B and condition B versus condition C), we used P < .025 as a critical level, following the Bonferroni rule, and had 80% power to detect a difference of 769 kJ.

	RESULTS

TOP ABSTRACT METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Eighteen of the 20 subjects (4 male subjects and 14 female subjects) enrolled in the study completed all of the study visits. Descriptive characteristics are presented in Table 3. One of the subjects was Hispanic or Latino (race not reported). Among the others, the racial distribution was as follows: 3 white, 11 black, 3 not reported. Subjects consumed a mean of 5809 ± 441 kJ at the baseline assessment visit, when instructed to eat as much or as little food as desired. The hunger and meal size ratings were 5.5 ± 0.6 cm and 7.6 ± 0.5 cm, respectively.

	DISCUSSION

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It could be argued that the very business model of the fast food industry promotes gorging. Advertising campaigns frequently emphasize the extra value of enormous portion sizes offered for an apparently minimal increase in cost over smaller orders.²⁶ Free beverage refills in some establishments exemplify this strategy. Moreover, the industry was founded on the premise of quick service, as conveyed by the term "fast food," and relies on rapid customer turnover to secure profits.^32,33

Large portion sizes^8,9,18,19 and a rapid eating rate^8,10 were shown previously to promote excess energy intake under various conditions. Moreover, strategies aimed at portion control consistently curb energy intake, presumably because of lack of available food. In contrast to previous studies,^8,9,18,19 our aim was not to evaluate whether adolescents consume less when given smaller absolute amounts of foods and beverage but rather to explore the effects of portioning and eating rate while eliminating confounding by amounts provided. In the present study, energy intake during a fast food meal was not influenced by portioning (condition A versus condition B) or eating rate (condition B versus condition C). Assuming a dietary pattern of 3 meals and 1 or 2 snacks per day, the average meal size to achieve energy balance would be 25% to 30% of total energy needs, equating to 2730 to 3275 kJ on the basis of the estimated energy expenditure for subjects in the present study. Given that subjects consumed 5460 kJ under all conditions, they overate regardless of manipulations in food presentation. Subjects recalled fast food intake more accurately after condition C, compared with condition A, presumably because portioning and slowing the eating rate, in combination, provide visual cues that enhance awareness of intake. Nevertheless, meal size ratings did not differ across conditions, and any increase in awareness clearly had no effect on total energy intake.

Our findings do not simply reflect the "clean plate phenomenon" (ie, consuming all food provided, regardless of amounts), because all subjects had leftovers on their trays or in their lunch boxes at the end of every fast food meal. Therefore, subjects might have eaten to their physical limits at all test visits. To evaluate this possibility, we estimated the volumes corresponding to the gram weights of consumed foods and beverage, assuming that the average density after chewing and swallowing is 1 g/mL. The total volume consumed, averaged across all 3 conditions, was 1074 mL. Although our calculations do not account for gastric emptying during the meals, this figure compares to the maximal capacity of the stomach (800–1000 mL) based on maximal ratings of abdominal discomfort in gastric distention studies of obese individuals.^34,35 Moreover, energy intake during the test visits was similar to what we observed during the baseline assessment visit, when food was replaced continuously to ensure that subjects never had a clean plate.

The propensity of overweight individuals to consume large amounts is not restricted to fast food meals. However, eating foods with low energy density (such as fruits, vegetables, legumes, and minimally processed grain products), even to physical limits, would not promote excess energy intake to the same extent as consuming conventional fast food.³⁶ The energy density of fast food is extremely high, relative to prevailing dietary patterns,³⁷ because of its very low content of water and fiber and very high content of fat, starch, and added sugar. Moreover, chemical manipulations often are used to achieve high palatability,³³ which also may promote excess energy intake.¹²

Several issues pertaining to the study design warrant comment. Strengths include the naturalistic setting of a food court for implementing the feeding protocols and a crossover design for hypothesis testing, thereby minimizing the possibility of confounding by demographic and behavioral variables. Limitations include a small sample size, restricting generalizability, and evaluation of only 1 combination of fast food menu items.

	CONCLUSIONS

TOP ABSTRACT METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Portioning menu items and slowing the eating rate did not decrease energy intake during a fast food meal. Our findings suggest that excess energy intake during an extra-large fast food meal is not attributable simply to distorted visual cues regarding consumption of foods and beverage or inadequate time for development of satiety signals. Rather, inherent characteristics related to the nutritional composition of conventional fast food likely promote excess energy intake. Although we cannot dismiss the potential public health benefits of strategies aimed at portion control, such as eliminating extra-large meals from fast food menus, fundamental improvements in the nutritional quality of fast food may be necessary to diminish the reported contribution of fast food to energy intake and risk for obesity.^7,25,37

	ACKNOWLEDGMENTS

 
This study was supported by grant P30 DK40561 awarded by the National Institutes of Health (Bethesda, MD) to support the Harvard Clinical Nutrition Research Center; the Charles H. Hood Foundation (Boston, MA); grant M01 RR02172 awarded by the National Institutes of Health (Bethesda, MD) to support the General Clinical Research Center at Children's Hospital Boston (Boston, MA); and grant R01 DK59240 awarded by the National Institute of Diabetes and Digestive and Kidney Diseases (Bethesda, MD).

	FOOTNOTES

 
Accepted Dec 15, 2006.

Address correspondence to Cara B. Ebbeling, PhD, Department of Medicine, Children's Hospital, 300 Longwood Ave, Boston, MA 02115. E-mail: cara.ebbeling{at}childrens.harvard.edu

Financial Disclosure: Dr Ludwig wrote a book on childhood obesity.

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TOP ABSTRACT METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

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