Consumer understanding of calorie amounts and serving size: implications for nutritional labelling.
Vanderlee, Lana ; Goodman, Samantha ; Yang, Wiworn Sae 等
Obesity is a growing public health problem. In Canada, more than
two thirds of adults are overweight or obese. (1) Excess energy intake
is a main driver behind the obesity epidemic. (2) Increased consumption
of sugar-sweetened beverages, including soft drinks, is a potentially
important contributor to increased energy intake. (3) Sugar-sweetened
beverages are characterized by high caloric content with little to no
nutritional value. (1) In North America, beverages are often sold in
large containers holding several times the recommended serving. An
American study suggested that actual soft drink portion sizes exceeded
the federally recommended standard portion sizes by 35-103%. (4)
Nutrition information on pre-packaged foods is mandatory in most
high-income countries. (5) In Canada, the Nutrition Facts Table must
appear on the back or side of all pre-packaged food items and is the
primary source of nutrition information for Canadian consumers. (6,7)
The Nutrition Facts Table uses serving size labelling, which displays
the nutrition information for a single serving of the product. Serving
size labelling aims to address "portion distortion", a
phenomenon whereby individuals perceive large portion sizes as
appropriate amounts to eat at a single eating occasion. (8) Current
Canadian labelling regulations allow a range of serving sizes to be
displayed for different items. For example, servings of non-carbonated
and carbonated beverages can range from 250 mL to 375 mL, and are
selected at the discretion of the manufacturer. (9) Several studies have
shown that consumers have difficulty interpreting serving size
information. (10,11) A cross-sectional study examining health label
literacy found that difficulty with serving sizes and incorrect
calculations were the primary reason for errors in inter preting
nutrition content. (12) A recent study found that only 37% of
individuals could correctly identify the amount of carbohydrates in a
20-oz multiple-serving beverage container. (13) Qualitative research
commissioned by Health Canada also indicates that inconsistent serving
sizes for similar products are a point of confusion for Canadians in
trying to understand the Nutrition Facts Table. (14) Across studies,
lower levels of comprehension have been associated with lower income,
education, literacy and numeracy skills. (5,12,13)
Front-of-package labelling has been introduced as a simplified
method of informing consumers about the calorie and nutrient content of
packaged foods. Several large food and beverage companies have recently
launched large front-of-package campaigns. One such initiative is the
Clear of Calories campaign, launched by the American and Canadian
Beverage Associations and implemented by leading companies, including
The Coca-Cola Company and PepsiCo. (15) The voluntary program
prominently displays calorie and serving size information on the front
label of beverage containers. In Canada, some beverages are labelled
with the calorie content of the entire bottle, while others are labelled
per 250 mL or 355 mL serving, similar to the information presented in
the Nutrition Facts Table.
To date, there is no published evidence examining consumer
understanding of these industry labelling schemes in Canada. The current
study sought to examine calorie estimation of beverage products with
various serving sizes. The study examined consumers' ability to
correctly identify calorie content in beverages when presented with
calories per serving or per container of actual Coke products. The study
also examined potential differences in consumer understanding when the
consumer is shown the government-mandated Nutrition Facts Table on the
back of containers, versus the front-of-pack labelling scheme currently
appearing on Coke[R] products. Finally, the study examined individual
differences in consumer understanding by socio-demographic factors.
METHODS
Sample description
A total of 687 participants from a national sample of Canadians
were recruited using an online commercial panel consisting of over
400,000 consumers through Global Market Insite, Inc. (GMI, Bellevue,
Washington). (16) Invitations to participate in the web-survey were
emailed to panel members over the age of 18; the invitation did not
indicate the nature or purpose of the study. (16) The current study was
part of a larger study on the marketing of children's food
products, and was completed online. Participants were eligible for the
study if they were over the age of 18, a parent of at least one child
between 4-10 years of age, and the primary shopper for their household.
This study received ethics clearance from the University of Waterloo
Office of Research Ethics.
Study protocol
Participants were randomized to view a Coke[R] beverage in one of
four labelling conditions: 1) a 591 mL bottle with front-of-package
calorie information per serving, 2) a 591 mL bottle with
front-of-package calorie information per container, 3) a 591 mL bottle
with the Nutrition Facts Table per serving, and 4) a 591 mL bottle with
the Nutrition Facts Table per container.
Measures
Demographics
Demographic information of participants included sex, age (18-34,
35-44, and [greater than or equal to]45), education (high school or
less, certificate or diploma, bachelor's degree, or university
degree or certificate greater than a bachelor's degree), ethnicity
(White or other) and income (<$40,000, $40,000-$80,000, or
>$80,000 annually). Self-reported height and weight were collected to
calculate body mass index (BMI) using categories defined by the World
Health Organization. (17)
[FIGURE 1 OMITTED]
Nutritional Knowledge, Understanding of Nutrition Labels and
General Health
Nutrition label use was assessed by the question, "When
shopping for food, do you usually look at the nutrition information
provided on the package?", with a 5-point Likert scale (1=never;
5=always). Perceived nutritional knowledge was examined using the
statement, "I am knowledgeable about health and nutrition
issues", using a 5-point Likert scale (1=strongly agree; 5=strongly
disagree). A measure of perceived general health was assessed by asking,
"In general, how would you rate your overall health?", with a
5-point Likert scale (1=poor; 5=excellent).
Calorie Content
Participants were asked "How many calories are in this bottle
of Coke[R]?", with an open response field in which participants
could fill in a number of calories. This question was asked while the
image of the Coke[R] bottle and calorie information were displayed on
the screen.
Analysis
Chi-square tests were used to test for demographic differences
between experimental conditions. Logistic regression modelling was used
to test for differences in the proportion of individuals who responded
correctly. Two outcomes were used: an exact response (260 calories) and
a more lenient "range" measure, where a correct response was
defined as a response within a 10-calorie range above or below the
correct answer (1=correct response; 0=incorrect response). Patterns of
significance were the same for both outcome measures; therefore results
are reported only for exact correct responses. Odds ratios (OR) and 95%
confidence intervals (95% CI) are reported. Labelling location
(front-of-package=0, Nutrition Facts Table=1), serving size portion
(entire container=0, single serving=1), socio-demographic variables
(age, sex, education, BMI, ethnicity, income), perceived nutrition
knowledge, label use and perceived general health were included in the
regression model. All analyses were conducted using SPSS v.20 (IBM
Corp., Somers, NY).
[FIGURE 2 OMITTED]
RESULTS
Sample characteristics are shown in Table 1. There were no
significant differences between conditions for any demographic measures.
Across all four conditions, 54.2% (n=372) of participants correctly
identified the exact number of calories in the entire beverage container
and 61.0% (n=419) were able to identify the number of calories within a
10-calorie range of the correct answer. Of the entire sample, 35.8%
underestimated and 10% overestimated the calorie content.
Table 2 shows the proportion of correct responses, underestimation
and overestimation for each experimental condition. Figure 2 also
illustrates the overall effect of labelling conditions on correct
estimation of calorie content of the container. Participants were able
to correctly identify the exact calorie content of the entire beverage
container 59.0% of the time when presented with the back-of-package
Nutrition Facts Table, and 49.1% of the time when viewing the
front-of-package industry labelling. In conditions with per container
labelling, 91.8% of participants correctly identified the calorie
content of the bottle, compared to 11.8% of participants who saw per
servinglabelling.
A logistic regression model was conducted to test for differences
in the proportion of participants who could correctly identify the
calorie amount between experimental conditions (where 0=incorrect
calorie amount and 1=correct calorie amount), adjusting for age group,
sex, BMI, education level, income, ethnicity, perceived nutritional
knowledge, frequency of label use, and perceived general health. Both
portion labelled (serving vs. container) and type of label (Nutrition
Facts Table vs. industry label) were significant. Participants who
viewed calories per container were significantly more likely to
correctly estimate the calories per container compared to those who
viewed the calories per serving (OR=242.9, 95% CI: 112.1-526.2,
p<0.001). Those who viewed the government-mandated Nutrition Facts
Table were significantly more likely to answer correctly than those who
saw voluntary front-of-package labelling (OR=5.3, 95% CI: 2.6-10.6,
p<0.001). There were no significant overall differences in correctly
estimating calorie content for the demographic measures age, sex,
education, BMI, ethnicity, income, nutrition label use and perceived
nutritional knowledge or health.
DISCUSSION
Overall, almost half of participants were not able to correctly
identify the calories in commonly consumed beverage containers when
viewing nutrition labels. In addition, approximately one in ten Canadian
parents of children ages 4-10 could correctly identify calorie content
when the serving size was less than the entire container. This was true
regardless of whether they viewed the government-mandated Nutrition
Facts Table on the back of containers or the front-of-pack calorie
labels voluntarily provided by manufacturers. There was slightly
improved performance with the use of the Nutrition Facts Table compared
to the front-of-package labelling in both per servingand per container
conditions. This likely reflects consumer familiarity with the Nutrition
Facts Table, as it has been mandatory in Canada since 2003.
Several factors could account for the high proportion of incorrect
responses. First, the "per serving" information on the Coke[R]
containers was written in very small and often blurry text. Prior to the
study, we visited several stores and were unable to find bottles with
more legible calorie labels, suggesting that this is likely
representative of challenges consumers face. Second, respondents who
attempted to use the serving size information may have had difficulty
calculating the total number of calories due to poor numeracy skills, as
higher numeracy rates have previously been associated with higher label
comprehension. (14) This is unlikely in this study, as the education
level of the sample was higher than that of the general Canadian public.
Finally, the serving size used on the many beverage containers may be
counter-intuitive to consumers. The existing regulations in Canada allow
the same product to display different serving sizes when sold in
different containers. For example, at the time of the study, Coke[R]
products were labelled as per serving for 591 mL bottles, and per
container for 355 mL cans. As a result, a higher calorie number was
posted on cans (160 calories) than on the larger bottle container (110
calories per serving). At the time of the study, the 591 mL container
included 2.4 servings; however, many respondents may have assumed that
the labelled amount was for the entire container. Previous research has
found that less than 40% of individuals correctly acknowledged multiple
servings in multi-serving food and beverage products. (11,18) This is
consistent with the current findings: more than 40% of participants who
viewed the "110 calories per serving" label estimated the
content of the bottle to be 110 calories. This suggests that labelling
per serving may systematically lead consumers to underestimate the
calorie content of products, and this may contribute to higher levels of
consumption.
Strengths and limitations
The sample was limited to parents of children aged 4-10 years. In
addition, the online survey did not allow participants to pick up and
examine the container. This may have reduced the accuracy of calorie
estimates; however, the study also served to focus attention on the
calorie information and likely resulted in increased attention and
scrutiny than would be typical in a naturalistic setting. Finally, the
online sample had somewhat higher-than-average levels of education and
income compared to the general population. (19) Previous research has
noted that those with higher levels of income and education generally
perform better on nutritional labelling tasks. (13) Poor performance on
this task among a more educated sample suggests that the accuracy of
calorie estimates could be even lower in the general population.
Strengths of the study include the use of a large national sample and
the use of actual product labels currently available on the Canadian
market. The between-conditions experimental design is also a
considerable strength in terms of drawing inferences about the impact of
different labelling formats.
CONCLUSION
Nutrition labels are only one of many approaches that will be
required to address obesity at a population level. However, for this
approach to be effective, consumers must be able to easily identify and
understand information on product labels. The current study suggests
that government-mandated nutrition labelling practices are confusing to
Canadians. Very few individuals were able to use the information in the
Nutrition Facts Table to calculate calorie content when there was more
than one serving per container. Voluntary industry measures appear to be
even less effective and can lead to dramatic underestimates of calorie
intake.
Given steadily increasing rates of obesity, these findings
highlight the need for substantive changes to the nutrition labelling of
pre-packaged food and beverages in Canada. The findings suggest that
providing calorie amounts for the entire container can dramatically
increase the accuracy of calorie estimates. For products that clearly
include multiple servings and for which serving sizes equivalent to the
entire container are not appropriate, more intuitive labelling should be
considered. An alternative is dual-column labels, which display
nutritional information for one serving of a product in addition to
information for the entire package. (20) At the very least, serving
sizes should be standardized within product categories. Finally,
voluntary industry labelling should be subjected to greater scrutiny to
ensure that the labels enhance rather than reduce consumer understanding
of nutrition information.
Acknowledgements: The authors thank Samantha Daniel for technical
assistance with the manuscript. This research was supported by a grant
from Canadian Cancer Society Research Institute, as well as CIHR
Master's Award (Vanderlee, Goodman, Sae Yang), the Heart and Stroke
Foundation of Canada and the CIHR/Training Grant in Population
Intervention for Chronic Disease Prevention: A Pan-Canadian Program
(Grant #: 53893) (Vanderlee, Goodman, Sae Yang), Ontario Graduate
Scholarships (Vanderlee, Goodman), Vanier Canada Graduate Scholarship
(Vanderlee), the Propel Centre for Population Health Impact, a Canadian
Institutes of Health Research New Investigator Award (Hammond), and a
Canadian Cancer Society Research Institute Junior Investigator Research
Award (Hammond).
Conflict of Interest: None to declare.
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Received: January 4, 2012
Accepted: June 10, 2012
Lana Vanderlee, BSc, [1] Samantha Goodman, MSc, [2] Wiworn Sae
Yang, MSc [1], David Hammond, PhD [1]
Author Affiliations
[1.] School of Public Health and Health Systems, University of
Waterloo, Waterloo, ON
[2.] Family Relations and Applied Nutrition, University of Guelph,
Guelph, ON
Correspondence: David Hammond, School of Public Health and Health
Systems, University of Waterloo, Waterloo, ON N2L 3G1, Tel:
519-888-4567, ext. 36462, Fax: 519-886-6424, E-mail:
dhammond@uwaterloo.ca
Table 1. Sample Characteristics (N=687)
Experimental Conditions
FOP/serving FOP/ Nutrition
container Facts/serving
n=153 n=183 n=171
Sex % (n) % (n) % (n)
Female 77.1% (118) 73.8% (135) 77.2% (132)
Male 22.9% (35) 26.2% (48) 22.8% (39)
Age (years)
18-34 32.0% (49) 32.8% (60) 34.4% (59)
35-44 49.7% (76) 51.4% (94) 52.6% (90)
[greater than 18.3% (28) 15.8% (29) 12.9% (22)
or equal to]45
BMI *
Underweight 2.6% (4) 1.6% (3) 4.7% (8)
Normal 49.7% (76) 41.0% (75) 47.4% (81)
Overweight 23.5% (36) 33.9% (62) 26.9% (46)
Obese 23.5% (36) 21.3% (39) 19.9% (34)
Not reported 0.7% (1) 2.2% (4) 1.2% (2)
Education
High school or less 30.1% (46) 24.6% (45) 15.2% (26)
Certificate or 42.5% (65) 39.3% (72) 48.0% (82)
diploma
Bachelor's Degree 17.6% (27) 27.3% (50) 23.4% (40)
University degree 9.2% (14) 7.7% (14) 13.5% (23)
greater than
bachelor's degree
Not reported 0.7% (1) 1.1% (2) 0% (0)
Income
<$40,000 22.9% (35) 23.5% (43) 19.9% (34)
$40,000-$80,000 36.6% (56) 34.4% (63) 34.5% (59)
>$80,000 32.0% (49) 32.2% (59) 39.8% (68)
Not reported 8.5% (13) 9.8% (18) 5.8% (10)
Ethnicity
White 73.9% (113) 71.6% (131) 77.2% (132)
Other 24.8% (38) 26.8% (49) 22.2% (38)
Not reported 1.3% (2) 1.6% (3) 0.6% (1)
Experimental Conditions
Nutrition Overall
Facts/container
n=180 N=687
Sex % (n) % (n)
Female 77.2% (141) 76.6% (526)
Male 22.8% (39) 23.4% (161)
Age (years)
18-34 29.4% (53) 32.2% (221)
35-44 55.0% (99) 52.3% (359)
[greater than 15.6% (28) 15.6% (107)
or equal to]45
BMI *
Underweight 2.8% (5) 2.9% (20)
Normal 51.4% (93) 47.3% (325)
Overweight 22.8% (41) 26.9% (185)
Obese 20.6% (37) 21.3% (146)
Not reported 2.2% (4) 1.6% (11)
Education
High school or less 25.6% (46) 23.7% (163)
Certificate or 36.7% (66) 41.5% (285)
diploma
Bachelor's Degree 22.8% (41) 23.0% (158)
University degree 14.4% (26) 11.2% (77)
greater than
bachelor's degree
Not reported 0.6% (1) 0.6% (4)
Income
<$40,000 23.9% (43) 22.6% (155)
$40,000-$80,000 29.4% (53) 33.6% (231)
>$80,000 34.5% (62) 34.6% (238)
Not reported 12.2% (22) 9.2% (63)
Ethnicity
White 77.2% (139) 75.0% (515)
Other 21.7% (39) 23.9% (164)
Not reported 1.1% (2) 1.2% (8)
FOP = Front-of-package, industry-led voluntary labelling; Nutrition
Facts = government-mandated labelling.
* BMI categories: Underweight = BMI <18.5; Normal weight = BMI
18.5-24.99; Overweight = BMI 25-29.99; Obese = BMI [greater than or
equal to]30.
Table 2. Estimation of Calorie Content by Experimental Condition
(N=687)
% Underestimated % Overestimated % Correct
% (n) % (n) % (n)
Labelling Condition
Front of Package 71.9% (110) 21.6% (33) 6.5% (10)
per serving
FOP per container 5.5% (10) 9.8% (18) 84.7% (155)
Nutrition Facts 73.7% (126) 9.9% (17) 16.4% (28)
per serving
Nutrition Facts 0% (0) 0.6% (1) 99.4% (179)
per container
Overall 35.8% (246) 10.0% (69) 54.2% (372)
