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Adolescent Vegetarians
How Well Do Their Dietary Patterns Meet the Healthy People 2010 Objectives?
Cheryl L. Perry, PhD;
Maureen T. McGuire, PhD;
Dianne Neumark-Sztainer, PhD, RD;
Mary Story, PhD, RD
Arch Pediatr Adolesc Med. 2002;156:431-437.
ABSTRACT
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Objectives To examine whether adolescent vegetarians were more likely than nonvegetarian
peers to meet the dietary recommendations of the Healthy People 2010 objectives
and to examine differences in other nutrients between these 2 groups.
Design A total of 4746 adolescents from 31 middle and high schools in the Twin
Cities area of Minnesota. Data were collected via self-report surveys, with
a student response rate of 81.5%.
Setting Urban secondary schools.
Participants Participants were equally divided by sex. The mean age was 14.9 years;
34.3% were in junior high school and 65.7% in high school. The racial/ethnic
distribution was 48.5% white, 19.0% African American, 19.2% Asian American,
5.8% Hispanic, 3.5% American Indian, and 3.9% mixed or other.
Main Outcome Measures Questions on vegetarian status and whether particular foods (eggs, dairy
foods, chicken, fish) were excluded. Dietary intake was assessed using the
Youth and Adolescent Food Frequency Questionnaire.
Results Vegetarian adolescents were significantly more likely than nonvegetarian
adolescents to meet the Healthy People 2010 objectives. This was particularly
noteworthy for total fat (70% vs 48%), saturated fat (65% vs 39%), daily servings
of vegetables (26% vs 14%), and 5 or more servings of fruits and vegetables
(39% vs 28%). Vegetarians were also less likely to eat fast food or drink
regular soda and fruit drinks. Vegetarians consumed less vitamin B12, more diet soda, more caffeine, and more iron.
Conclusion Adolescent vegetarians have a dietary pattern that is more likely than
nonvegetarians to meet the Healthy People 2010 objectives.
INTRODUCTION
VEGETARIANS, for a variety of reasons, choose to limit their intake
of meat and other animal products.1 Some vegetarians
eat no animal products (vegans), whereas others include milk products (lactovegetarians)
or eggs (ovovegetarians). Many self-identified vegetarians also eat some meat,
particularly fish and chicken (semivegetarians).1
Adult vegetarianism has been studied for the relationships among a plant-based
diet, chronic diseases, and length of life.2
Overall, adult vegetarians tend to live significantly longer lives than nonvegetarians,
with substantially lower rates of cardiovascular diseases, hypertension, type
2 diabetes mellitus, obesity, and some types of cancer.3-7
Vegetarian diets, like all diets, need to be planned appropriately to
be nutritionally adequate. Of concern with adult vegetarians is sufficient
consumption of nutrients often found in animal products.8
Nutrients of most concern include iron, calcium, zinc, and vitamin B12.7-9 White
and Frank1 point out that clinical nutrition
deficiencies are uncommon even among vegans, although they suggest that careful
planning and, in some cases, vitamin supplementation may be warranted. The
intake of these nutrients has not been examined in a large adolescent vegetarian
population.
Given that dietary patterns are adopted and appear to be maintained
during adolescence and young adulthood,10-12
an interesting question is whether younger vegetarians report healthier dietary
patterns than nonvegetarian counterparts. Specifically, what percentage of
adolescent vegetarians (vs nonvegetarians) comply with the dietary recommendations
outlined in the Healthy People 2010 objectives? Do adolescent vegetarians
consume less fat and saturated fat, consume more fruits and vegetables and
fiber, and maintain healthier intake levels of other nutrients, such as calcium,
than do adolescent nonvegetarians? Or, alternatively, are adolescent vegetarians
at increased risk for inadequate intake of any of these foods or nutrients?
These questions are important since dietary behaviors have implications for
adolescents' current and future health.11, 13-16
In a prior study, Neumark-Sztainer et al17
found that adolescent vegetarians were twice as likely to consume fruits and
vegetables, one third as likely to consume sweets, less likely to consume
dairy products, and one fourth as likely to consume salty snack foods compared
with nonvegetarians. Donovan and Gibson18 found
that mean daily intakes of energy and most nutrients were comparable for vegetarians
and nonvegetarian adolescents. Adolescent vegetarians in their study, however,
consumed fewer dairy products, meat, and sweets and more legumes, nuts, and
vegetables than did nonvegetarians.18 The studies
with adolescent vegetarians, however, have been limited in their assessment
of diet, had small samples of vegetarians, and have not included a multiracial,
multiethnic group of subjects.
Data for the current study were drawn from Project EAT (Eating Among
Teens), a comprehensive study of adolescent eating patterns and weight concerns.19 A large group of urban adolescents from multiple
ethnic groups in this study provided the opportunity to examine the eating
patterns and nutrient intake of a diverse population of adolescents. We hypothesized
that adolescents who reported to be vegetarians, compared with nonvegetarian
peers, would be more likely to meet the dietary recommendations of the Healthy
People 2010 objectives but might eat less of some nutrients, particularly
calcium, iron, vitamin B6, and possibly vitamin B12.
Finally, we hypothesized that more stringent vegetarians, those who did not
eat fish and chicken, would be more likely to meet the dietary recommendations
of Healthy People 2010 related to fat, fruits, and vegetables.
POPULATION AND METHODS
SAMPLE AND STUDY DESIGN
The study population included 4746 adolescents from 31 public middle
schools and high schools in the Twin Cities area of Minnesota. Participants
were equally divided by sex (50.2% male, 49.8% female). The mean age of the
study population was 14.9 years (range, 11-18 years); 34.3% were in junior
high school and 65.7% in high school. The racial/ethnic backgrounds of the
participants were as follows: 48.5% white, 19.0% African American, 19.2% Asian
American, 5.8% Hispanic, 3.5% American Indian, and 3.9% mixed or other. Most
of the Asian American population was from Southeast Asia.
Data for this study were collected via self-report surveys and anthropometric
assessments in the 1998-1999 school year. The data were collected in schools
within health, physical education, and science classrooms in one 90-minute
period or two 50-minute periods. Trained research staff administered the surveys
in the classrooms and measured height and weight in a private area. Study
procedures were approved by the University of Minnesota Human Subjects' Committee
and by research boards of the participating school districts. Consent procedures
also followed the requirements of the participating school districts. In some
schools, passive consent procedures were used, whereas in others active consent
procedures were required. The response rate for student participation was
81.5%. The main reasons for lack of participation were absenteeism and failure
to return consent forms within schools requiring active consent.
MEASURES
Vegetarian Items
To identify vegetarians, all students were asked on the survey to respond
yes or no to the question, "Are you a vegetarian?" Those who answered yes
were asked to respond to additional questions. The first was "As a vegetarian,
do you eat any of the following? (1) Eggs; (2) Dairy food (such as milk, cheese);
(3) Chicken; (4) Fish." Students who checked no to chicken and fish were labeled
lacto-ovo-vegans. Students who checked yes to either chicken or fish were
labeled semivegetarians.
Sociodemographic Items
Demographic factors, including sex, ethnicity/race, school level, and
socioeconomic status (SES), were based on self-report. Ethnicity/race was
assessed with the question, "Do you think of yourself as . . . (1) White;
(2) Black or African American; (3) Hispanic or Latino; (4) Asian American;
(5) Hawaiian or Pacific Islander; or (6) American Indian or Native American?"
Youth were given the option of choosing multiple responses, and those reporting
more than one response (other than white) were coded as mixed or other. School
level was divided into middle school (7th through 8th grades) and high school
(9th through 12th grades). The prime determinant of SES was parental educational
level, defined by the higher level of either parent. Response categories for
questions on parental educational level were as follows: (1) did not finish
high school; (2) finished high school or received general equivalency diploma;
(3) some college; (4) finished college; (5) master's or PhD degree; and (6)
don't know. Other variables used to assess SES included the following: family
eligibility for public assistance (yes, no, or don't know), eligibility for
free or reduced-cost school meals (yes, no, or don't know), and employment
status of mother and father (full-time, part-time, networking, or don't know).
An algorithm was developed to avoid classifying adolescents as having high
SES, based on parental education levels, if they were receiving public assistance,
eligible for free or reduced-cost school meals, or had 2 unemployed parents
(or 1 unemployed parent if from a single-parent household). Students were
classified as having low SES, middle SES, or high SES.
Dietary Intake
Assessment of dietary intake was performed with the 149-item Youth and
Adolescent Food Frequency Questionnaire (YAQ). The YAQ asks about specific
food items, identifies amounts of each food, and asks for frequency of consumption.
For example, one question asks about how frequently 2 pieces of pizza are
consumed (never, 1-3 times per month, once a week, 2-4 times per week,  5
times per week). Validity and reliability of the YAQ have been tested among
a random sample of children (aged 9-18 years) of participants in the Nurse's
Health Study and found to be within acceptable ranges for dietary assessment
tools.20-21 Mean correlation for
energy-adjusted nutrients between two YAQs and three 24-hour recalls (implemented
in 3 seasons) was 0.45. The mean energy intake (in calories) for the YAQ was
higher than for the recalls but within 1% of them. Test-retest correlations
between 2 YAQs during a 1-year period were 0.49 for fruit and 0.48 for vegetables.
Responses to questions on the frequency of intake of the following fruits
and vegetables were summed to assess average total daily intake of fruits
and vegetables: apples, apple juice, bananas, beets, broccoli, carrots, celery,
coleslaw, corn, grapes, greens or kale, lettuce, melon, mixed vegetables,
oranges, orange juice, peaches or plums, pears, peas, peppers, potatoes (not
including French fries), raisins, spinach, strawberries, string beans, tomatoes,
tomato or spaghetti sauce, yams, and zucchini or squash. Consumption of fruits
and vegetables was generally reported using 5-point scales (eg, never or less
than once a month, 1-3 times per month, once a week, 2-4 times per week, 5
times per week).
Dietary intake in the present study was evaluated in 2 ways: relative
to the Healthy People 2010 objectives (for relevant nutrients and foods) and
as mean daily intake. In the current study, nutrient and food behaviors examined
relative to the Healthy People 2010 objectives included the following: total
fat (percentage of total energy), saturated fat (percentage of total energy),
calcium (milligrams), fruits (servings), vegetables (servings), and grains
(servings). These were converted to the percentage of students who complied
with the Healthy People 2010 objectives. Other daily nutrient intakes included
the following: calories (kilocalories), protein (grams), calcium (milligrams),
zinc (milligrams), iron (milligrams), vitamin A (units), vitamin B6
(milligrams), vitamin B12 (micrograms), vitamin C (milligrams),
folate (micrograms), linoleic acid (grams), cholesterol (milligrams), caffeine
(milligrams), and fiber (grams). Other daily food intakes included soda (daily
servings), diet soda (daily servings), fruit drink (noncarbonated, daily servings),
and fast food (frequency in the past week). We also examined the percentage
of calories from protein, carbohydrates, total fat, saturated fat, polyunsaturated
fat, and monounsaturated fat, as well as the average daily servings of fruit
and vegetables. These were selected to assess whether vegetarians were at
greater or lesser risk than nonvegetarians for nutrient inadequacies of particular
concern during adolescence.
DATA ANALYSES
The present study assessed dietary intake associated with adolescent
vegetarians. In the first set of analyses, the percentages of adolescents
who met the Healthy People 2010 dietary objectives were compared between vegetarians
and nonvegetarians. These analyses also assessed whether dietary intake was
moderated by sex (ie, sex-by-vegetarian interactions) or race/ethnicity (ie,
race/ethnicity–by–vegetarian interactions). Daily intake of specific
nutrients and foods was also compared between vegetarians and nonvegetarians.
In the second set of analyses, the percentages of adolescents who met Healthy
People 2010 objectives were compared between specific vegetarian groups. For
these analyses, vegetarians who were lacto-ovo-vegans were compared with semivegetarians.
Logistic and linear regression analyses were conducted to test for statistical
differences between the comparison groups when the dependent variables were
either dichotomous or linear, respectively. All analyses controlled for sex
and race since there were differences between groups in sex and racial make-up.
The interaction analyses by sex and race were controlled for race or sex,
respectively. P<.05 was considered significant. P values were not adjusted for multiple testing because
false-positive differences were unlikely when the P
values are small (<.01), which was the case for most of the comparisons.
All analyses were conducted using the Statistical Analysis System.22
RESULTS
From the total sample of students, 4521 adolescents had completed the
YAQ and had usable data, and 262 (5.8%) reported being vegetarian. Among the
vegetarians, nearly three fourths (73.7%) were female. Nearly half (47.5%)
of the vegetarians were white, 26.8% were Asian, 11.1% were African American,
5.8% were Hispanic, 5.0% were American Indian, and the remaining 4% were Hawaiian
or Pacific Islander or other. Because there were so few Hispanic, American
Indian, and mixed or other vegetarians (because of the sample sizes of those
race/ethnicities in the entire sample), these groups were combined and referred
to as other in the race/ethnicity analyses. Among the vegetarians, 38.6% were
in high school (vs middle or junior high school). More than half of the vegetarians
(62%) reported eating chicken and/or fish and were semivegetarians; 32% ate
eggs and/or dairy products (but not chicken or fish), and 6% were vegans,
so that 38% were classified as lacto-ovo-vegans for these analyses. As given
in Table 1, there were significant
differences between vegetarians and nonvegetarians in the sex and racial makeup
of the samples.
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Table 1. Demographic Comparisons of Vegetarian and Nonvegetarian Adolescents
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Overall, adolescent vegetarians were significantly more likely to meet
the dietary recommendations of Healthy People 2010 as given in Table 2. Vegetarian adolescents were more than twice as likely to
eat less than 30% of their calories from fat and nearly 3 times more likely
to eat less than 10% of their calories from saturated fat. They were also
1.4 to 2 times more likely to eat 2 or more servings of fruit, 3 or more servings
of vegetables, 3 or more servings of vegetables including 1 that is dark yellow
or green, and 5 or more servings of fruits and vegetables daily. There were
no significant differences in daily calcium intake or servings of grains.
There were also no significant sex–by–vegetarian status or race–by–vegetarian
status interactions.
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Table 2. Percentages of Adolescents Who Met Healthy People 2010 Objectives
by Vegetarian Status*
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Differences between vegetarians and nonvegetarians for a variety of
other food intake variables are given in Table 3. Vegetarian adolescents, compared with nonvegetarian adolescents,
consumed significantly less vitamin B12, cholesterol, regular soda,
fruit drink, and fast food, as well as the percentage of calories from protein
and all types of fat. Vegetarians were significantly more likely than nonvegetarians
to consume more iron, vitamin A, folate, caffeine, fiber, and diet soda, as
well as a greater percentage of calories from carbohydrates and more servings
of fruit and vegetables. There were nonsignificant differences between the
2 groups for calories, protein, calcium, zinc, vitamin B6, vitamin
C, and linoleic acid.
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Table 3. Differences in Selected Dietary Factors Between Vegetarians
and Nonvegetarians*
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Among the vegetarians, differences between the lacto-ovo-vegans and
semivegetarians (who ate chicken and/or fish) were examined. The results for
the percentage of each group who met the dietary guidelines of the Healthy
People 2010 objectives are given in Table
4. Lacto-ovo-vegans were more than twice as likely as semivegetarians
to eat less than 30% of the calories in their diet from fat, more than 2 servings
of fruit per day, and 5 or more servings of fruits and vegetables per day.
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Table 4. Percentages of Specific Types of Adolescent Vegetarians Who
Met Healthy People 2010 Objectives*
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Comparing lacto-ovo-vegans with semivegetarians, there were no interactions
between adherence to the Healthy People 2010 objectives by sex, but there
were 5 significant interactions by race. White semivegetarians were significantly
less likely than white lacto-ovo-vegans to meet the daily requirement for
calcium (22.6% vs 43.9%; odds ratio [OR], 0.37; 95% confidence interval [CI],
0.16-0.82), to eat more than 2 servings of fruit each day (34.5% vs 68.6%;
OR, 0.24; 95% CI, 0.11-0.54), to eat more than 3 servings of vegetables each
day (8.6% vs 35.3%; OR, 0.17; 95% CI, 0.06-0.49), to eat more than 3 vegetables
each day, including 1 deep yellow or green vegetable (6.2% vs 22.8%; OR, 0.22;
95% CI, 0.07-0.74), and to eat 6 or more servings of grains each day (30.0%
vs 53.7%; OR, 0.36; 95% CI, 0.17-0.79). There were no significant differences
between lacto-ovo-vegans and semivegetarians on these items among African
Americans, Asians, or others.
COMMENT
Overall, vegetarian adolescents were much more likely than nonvegetarians
to meet the Healthy People 2010 objectives. The percentage of vegetarians
vs nonvegetarians who met the objectives was particularly noteworthy for fat
consumption (70% vs 48%), saturated fat consumption (65% vs 39%), daily servings
of vegetables (26% vs 14%), and 5 or more daily servings of fruits and vegetables
(39% vs 28%). These are substantive differences in the major targeted dietary
behaviors for cardiovascular disease (fat intake) and cancer (fruit and vegetable
intake) and suggest that vegetarian adolescents, similar to their adult counterparts,
have dietary patterns that, if maintained, could significantly lower their
risk of the leading causes of death as adults.23-26
The results from the present study on dietary fat were corroborated
by comparing vegetarians' and nonvegetarians' average daily intake of fat.
On average, 26% of the vegetarians' total calories were from fat, compared
with 30% of nonvegetarians' calories, a 13% reduction in fat consumption.
More notably,27 vegetarians' intake of saturated
fat and cholesterol was 14% and 22% lower, respectively, than nonvegetarians.
Similar results were found for fruit and vegetable intake. Vegetarians,
compared with nonvegetarians, consumed 0.4 more servings of fruit and 0.5
more servings of vegetables daily. In fact, the lacto-ovo-vegans consumed
5.8 servings of fruits and vegetables per day. This can be compared with 4.1
servings for nonvegetarians and 4.7 servings for semivegetarians. Only the
lacto-ovo-vegans, those who did not eat chicken and/or fish, consumed, on
average, more than the recommended 5 servings of fruits and vegetables each
day.
The magnitude of the differences between vegetarians and nonvegetarians
for fat consumption and fruit and vegetable intake was substantial. For example,
the differences between vegetarians and nonvegetarians were greater for fat
consumption and vegetable intake than differences between male and female
adolescents, those with low SES and high SES, and white and black populations,
as reported in a prior study19 with this same
population. Although these are not ideal comparisons, they do provide population
groups that suggest how sizable the differences were between vegetarian and
nonvegetarian dietary patterns.
There were positive and negative aspects of the adolescent vegetarian
dietary patterns when examining other aspects of their diet. For example,
adolescent vegetarians were less likely than nonvegetarian peers to eat fast
food or drink soda and fruit drinks and more likely to consume more carbohydrates,
iron, fiber, and vitamin A. These dietary factors add to the picture of a
healthier overall dietary pattern for the vegetarians and are consistent with
the data on fat, fruits, and vegetables. It is particularly important that
iron intake was higher among vegetarians since the absorption of iron from
vegetable sources is generally lower than from meat sources.28
However, vegetarian adolescents, compared with nonvegetarians, consumed less
vitamin B12, which may be important for future health. Vegetarians
also consumed marginally less protein. They consumed, on average, 70 g of
protein (62 g for the lacto-ovo-vegans), which is sufficient for growth and
development.29 The recommended daily allowance
for protein for 15- to 18-year-olds is 44 g/d for girls and 59 g/d for boys.28 Although adequate protein is essential for growth,
plant sources of protein alone can provide adequate amounts of essential amino
acids if a variety of plant foods are consumed and energy needs are met.7
Most vegetarian (70%) and nonvegetarian (65%) adolescents did not meet
the recommended intake (1300 mg/d) for calcium. There were no significant
differences between vegetarian and nonvegetarian calcium intakes or between
lacto-ovo-vegans' and semivegetarians' calcium intakes. Other studies have
found that lacto-ovo-vegetarians have calcium intakes that are comparable
to or higher than those of nonvegetarians.30-31
To meet calcium requirements, adolescent vegetarians and nonvegetarians should
consume calcium-rich or calcium-fortified foods, or if they are unwilling
or unable to do this, they should take supplemental calcium.
There were few differences between lacto-ovo-vegans and semivegetarians.
As hypothesized, the lacto-ovo-vegans were more likely to meet the Healthy
People 2010 objectives for total fat, fruit, and 5 or more daily servings
of fruits and vegetables compared with semivegetarians.
It is important to address substantive differences between vegetarians
and nonvegetarians that might account for the dietary differences observed
in this study. These demographic and psychosocial differences were the focus
of a prior publication with this same population of students.32
The adolescent vegetarians were more likely than nonvegetarians to be female,
not African American, in middle school (rather than high school), weight and
body conscious, dissatisfied with their bodies, and involved in a variety
of healthy and unhealthy weight control behaviors. In addition, vegetarians
more often reported having been told by a physician that they had an eating
disorder and were more likely to have contemplated and attempted suicide.
Other behaviors, such as substance use and physical activity, were not different
between vegetarians and nonvegetarians. Thus, the adolescent vegetarians differ
from the nonvegetarians in being female (although it is noteworthy that the
relationship between vegetarian status and psychosocial factors did not differ
by sex) and in their focus on weight and diet and eating behaviors; this focus
on weight and diet seems to be the primary motivation for adopting a vegetarian
diet, rather than its long-term health benefits.17, 32-33
Health care practitioners should be aware of adolescents who greatly limit
food choices and who exhibit symptoms of eating disorders. However, data suggest
that vegetarian diets do not lead to eating disorders.7
Adolescents who adopt vegetarian eating habits without adequate nutrition
knowledge and with a desire to achieve weight loss are most vulnerable to
malnutrition and growth failure34 and should
receive added attention. Thus, although the adoption of a vegetarian-eating
pattern may have benefits in terms of nutritional intake for many adolescents,
for others it may be a method of unhealthy food restriction. Therefore, adolescents
who choose to become vegetarians should be monitored for adequate intake and
questioned about their motivations by a health care practitioner.
This study had several strengths and limitations. The questions on vegetarianism
and dietary factors were more comprehensive than prior population-based studies.
We chose a representative sample of adolescents from the major urban school
districts in Minnesota and thus had sufficient data to examine ethnic group
and sex differences. The study was limited by the self-reporting of vegetarianism
and the cross-sectional design of the study. Furthermore, although the YAQ
has been found to have acceptable reliability and validity,20-21
as with any dietary assessment tool, it has limitations. Specifically, it
is limited by its reliance on adolescents' recall, the lack of specificity
of portion sizes, and the inability to assess nutrient content of nonstandard
mixed dishes (such as homemade spinach lasagna). More work is needed on a
dietary measure than can be self-administered in a school setting and yet
can also provide more reliable and valid data.
In the current study, adolescent vegetarians were more likely than nonvegetarians
to be adhering to the Healthy People 2010 objectives relevant to nutritional
health. This was even more the case among the lacto-ovo-vegans. Thus, it seems
that rather than viewing adolescent vegetarianism as a difficult phase or
fad, the dietary pattern could be viewed as a healthy alternative to the traditional
American meat-based diet. With careful planning, using the vegetarian food
guide pyramid as a guide,35 vegetarian adolescents
could learn proper nutritional patterns and practices that could lead to a
lifelong dietary practice that might be salutary for themselves and their
families in the future.
| What This Study Adds
Few adolescents meet the dietary guidelines of the Healthy People 2010
objectives. Prior research has indicated that adolescent vegetarians may eat
more fruits and vegetables, fewer sweets, and fewer salty snack foods than
nonvegetarian peers. The previous studies of vegetarians were limited in their
assessment of diet, small samples of adolescents, and lack of representation
of multiple racial/ethnic groups. The present study examines the dietary patterns
of adolescent vegetarians and compares them with nonvegetarian adolescents
and the Healthy People 2010 objectives. The study is performed with a large,
multiethnic population in an urban area in the Upper Midwest. Adolescent vegetarians
were significantly more likely to meet the Healthy People 2010 objectives,
especially for fat intake and fruits and vegetables. This suggests that vegetarianism
may provide a healthy dietary pattern for adolescents, particularly if it
is well planned to address potential deficiencies.
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AUTHOR INFORMATION
Accepted for publication January 1, 2002.
This study was supported by grant MCJ-270834 (Dr Neumark-Sztainer) from
the Maternal and Child Health Bureau (Title V, Social Security Act), Health
Resources and Service Administration, US Department of Health and Human Services,
Washington, DC.
Corresponding author and reprints: Cheryl L. Perry, PhD, Division
of Epidemiology, School of Public Health, University of Minnesota, Minneapolis,
MN 55454 (e-mail: perry{at}epi.umn.edu).
From the Division of Epidemiology, School of Public Health, University
of Minnesota, Minneapolis.
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