nutrients
Article
Cardiorespiratory Fitness and Peak Torque
Differences between Vegetarian and Omnivore
Endurance Athletes: A Cross-Sectional Study
Heidi M. Lynch *, Christopher M. Wharton and Carol S. Johnston
Arizona State University, School of Nutrition and Health Promotion, Phoenix, AZ 85004, USA;
Christopher.Wharton@asu.edu (C.M.W.); Carol.Johnston@asu.edu (C.S.J.)
* Correspondence: Hnetland@asu.edu; Tel.: +1-847-828-1332
Received: 1 September 2016; Accepted: 10 November 2016; Published: 15 November 2016
Abstract: In spite of well-documented health beneﬁts of vegetarian diets, less is known regarding
the effects of these diets on athletic performance. In this cross-sectional study, we compared elite
vegetarian and omnivore adult endurance athletes for maximal oxygen uptake (VO2 max) and
strength. Twenty-seven vegetarian (VEG) and 43 omnivore (OMN) athletes were evaluated using
VO2 max testing on the treadmill, and strength assessment using a dynamometer to determine peak
torque for leg extensions. Dietary data were assessed using detailed seven-day food logs. Although
total protein intake was lower among vegetarians in comparison to omnivores, protein intake as
a function of body mass did not differ by group (1.2 ± 0.3 and 1.4 ± 0.5 g/kg body mass for VEG
and OMN respectively, p = 0.220). VO2 max differed for females by diet group (53.0 ± 6.9 and
47.1 ± 8.6 mL/kg/min for VEG and OMN respectively, p < 0.05) but not for males (62.6 ± 15.4 and
55.7 ± 8.4 mL/kg/min respectively). Peak torque did not differ signiﬁcantly between diet groups.
Results from this study indicate that vegetarian endurance athletes’ cardiorespiratory ﬁtness was
greater than that for their omnivorous counterparts, but that peak torque did not differ between diet
groups. These data suggest that vegetarian diets do not compromise performance outcomes and may
facilitate aerobic capacity in athletes.
Keywords: vegetarian; endurance; VO2 max; dynamometer; protein; sustainability; torque; body
composition; Dual X-ray Absorptiometry (DXA)
1. Introduction
Vegetarian diets are increasingly being adopted for a variety of reasons including health,
sustainability, and ethics-related concerns. Adherence to a vegetarian diet has been associated with a
reduced risk of developing coronary heart disease [1], breast cancer [2], colorectal cancers [3], prostate
cancer [4], type 2 diabetes [5], insulin resistance [6], hypertension [7], cataracts [8] and dementia [9].
Vegetarians also typically have a lower body mass index (BMI) [10] and an improved lipid proﬁle [11].
In addition to promoting physical health, reducing or eliminating meat from the diet is environmentally
advantageous since producing meat requires more land, water, and energy resources than growing
plants for food [12], and producing meat creates more greenhouse gases compared to a plant-based
diet [13,14].
In spite of the many health aspects of vegetarian diets some concern has been raised pertaining to
the nutrient adequacy of vegetarian diets for supporting athletic performance. Vegetarian diets are
typically lower in vitamin B12, protein, creatine, and carnitine [15,16], and iron and zinc from plant
sources are less bioavailable than from meat sources [17]. However, vegetarian diets are typically
higher in carbohydrate and antioxidants [18,19], which may be advantageous for athletic performance,
particularly for endurance activities [20].
Nutrients 2016, 8, 726; doi:10.3390/nu8110726
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Despite these issues, little research directly examining vegetarian diets and athletic performance is
available. There have been mixed results regarding hypertrophic potential when comparing vegetarian
diets with omnivore diets during resistive exercise training; however, in all cases these differences
did not translate to differential strength gains at the completion of the trials [21–24]. Adoption of
a lacto-ovo vegetarian (LOV) diet for six weeks did not signiﬁcantly affect endurance performance
among a group of trained, male endurance athletes, in spite of a decrease in total testosterone while on
the vegetarian diet [25]. There were also no group differences between 20 participants adopting an
LOV diet compared to maintaining their usual omnivorous diet in terms of muscle buffering capacity
in conjunction with sprint training for ﬁve weeks [26]. These studies provide some insight into the
effect of a vegetarian diet on athletic performance. However, a considerable limitation in many of
these studies is the inclusion of participants who typically consume meat but subsequently adopt
a vegetarian diet only for the duration of the study rather than comparing participants who have
adhered to a vegetarian or meat-containing diet long-term.
In a 1986 observational trial, Hanne and colleagues compared athletes who had maintained either
an LOV or omnivore diet for at least two years and found no group differences for aerobic or anaerobic
capacity [27]. However, aerobic capacity was estimated using cycle ergometry and predicted VO2
max, and strength or torque were not measured. Moreover, body adiposity was estimated using
skinfold thickness. Given the current interest in vegetarian diets, in terms of both long-term health
and environmental beneﬁts, it is important to reafﬁrm, using leading-edge technology, that high-level
athletic performance is supported by these diets.
The purpose of the present cross-sectional study was to examine body composition and
performance measures in vegetarian and omnivore adult endurance athletes who had adhered to
their respective diet plans for at least three months. Body composition, including visceral adiposity,
was measured using dual-energy X-ray absorptiometry (DXA), leg strength was measured using a
dynamometer, and aerobic capacity was determined using the Bruce protocol treadmill test. It was
hypothesized that there would be no differences between groups on any parameters.
2. Materials and Methods
2.1. Participant Recruitment
Healthy men and women,
both vegetarians and omnivores,
were recruited through
advertisements on Stevebay.org (a popular website for endurance athletes), Facebook, and through
word of mouth. Participants were either on a competitive club sports team at a National Collegiate
Athletic Association (NCAA) Division 1 university or training for a major endurance race (such as
a marathon, triathlon, cycling race, or other ultra-endurance event). An equal number of omnivore
and vegetarian athletes were enrolled in the study between the ages of 21–58 years (35 per group);
however, answers to diet questions indicated that eight of the vegetarians ate meat on occasion, and
these subjects were reclassiﬁed as omnivores. Participants completed a health history questionnaire
and were excluded if they had any chronic disease. All participants had the study verbally explained to
them and provided their written consent; this study was approved by the Institutional Review Board
at Arizona State University, number HS1211008557. Study recruitment and all study measurements
took place between August and November 2015.
2.2. Experimental Approach
In this cross-sectional investigation participants completed all study measurements in a single
visit. Prior to the visit, participants completed a seven-day food log. Fifty-seven out of seventy
participants returned completed food logs, all of which were used in dietary analysis using Food
Processor SQL Nutrition and Fitness Software by ESHA Research, Inc. (version 10.11.0, Salem, OR,
USA). Height and body mass were measured using a SECA directprint 284 digital measuring station
when participants were wearing light clothing and no shoes. Participants also completed a full-body
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DXA scan (Lunar iDXA, General Electric Company, East Cleavland, OH, USA), which was conducted
by a certiﬁed radiology technologist.
Maximal oxygen uptake was determined by following the Bruce protocol [28] on a Trackmaster
TMX425C treadmill using the Parvo Medics TrueOne 2400 (Sandy, UT, USA) metabolic measurement
system. Prior to beginning the test, participants were instructed how to report their fatigue level
using the Borg rating of perceived exertion (RPE) scale [29]. When asked by a research assistant, they
reported their RPE at the end of each minute of the test by pointing to a printed Borg RPE chart being
held by a research assistant. Participants were verbally encouraged by the research team to push as
long as they could and to try to reach a true maximal effort. Handrail support was not allowed during
the test. Maximal respiratory exchange ratio (RER) was recorded to help determine whether subjects
had reached a “true” maximal effort during the test. Maximal RER values of ≥1.1 were considered
indicative of true maximal oxygen uptake [30,31]. Peak oxygen uptake reported is the highest oxygen
uptake measured during the test.
Finally, participants completed a series of leg extensions and ﬂexions on the HumacNorm
isokinetic dynamometer (Computer Sports Medicine Inc. (CSMi, Stoughton, MA, USA) at 60 degrees
per second (d/s), 180 d/s, and 240 d/s. Participants were familiarized with the protocol and conducted
one practice repetition at each speed prior to performing three maximal effort repetitions at each speed.
All sets, including practice repetitions, were performed on both legs, and self-reported dominant side
was recorded. Participants moved from the VO2 max test immediately into the dynamometer testing,
and there were 30 s of rest between sets on the dynamometer.
2.3. Statistical Analyses
Based on the data of Hanne et al. [27], at 80% power and an alpha level of 5%, 15 participants per
group would be needed to detect a 10% difference in strength and 80 participants per group would be
needed to detect a 10% change in aerobic capacity between groups. Data were analyzed for normality
and log transformed if necessary, and outliers (values > 3 standard deviations (SD) from the mean)
were removed prior to data analyses. Data reported are the mean ± SD, and participant characteristics
are displayed by gender and diet group. A 2-way analysis of variance (ANOVA) analysis was used to
determine differences between diet groups for participant characteristics followed by an independent
t-test for post-hoc examination by diet within gender if indicated. Dietary data are reported by group,
and a general linear model analysis was used to examine differences between groups controlling
for gender. Data were analyzed using the Statistical Package for Social Sciences (SPSS) 23.0 for Mac
(SPSS, Inc., Chicago, IL, USA).
3. Results
In the vegetarian group, 24 of the 27 participants (89%) had adhered to a vegetarian diet
for >2 years. Of the remaining three participants, the diet had been followed for three, six, or eleven
months. Fifteen of the vegetarians were vegans (nine men and six women), and twelve were lacto-ovo
vegetarians (ﬁve men and seven women).
There were no signiﬁcant age or gender differences between groups (Table 1).
Signiﬁcant
differences were noted between diet groups for body mass and for lean body mass (LBM): female
vegetarians tended to have a lower total body mass and LBM compared to the female omnivores
(−11% and −7% respectively). Adiposity, however, did not differ between diet groups. Physical
activity levels, recorded as kcal·kg−1·week−1, were 20% higher for vegetarians compared to omnivores
(p = 0.018) (Table 1). Maximal oxygen uptake (mL/kg/min) differed signiﬁcantly between diet groups,
and post-hoc analyses revealed a signiﬁcantly greater aerobic capacity in the female vegetarians in
comparison to the female omnivores (+13%, p < 0.05) (Table 1); however, absolute maximal oxygen
uptake (L/min) did not differ between diet groups. Peak torque when doing leg extensions was
not different between diet groups. The 7-day diet records revealed several differences in nutrient
intake between diet groups. Although total energy intakes were similar between the diet groups,
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the vegetarians consumed more carbohydrate, ﬁber, and iron daily compared to omnivores (Table 2).
However, daily intakes for protein, saturated fat, cholesterol, vitamin B12, and selenium were lower
among the vegetarians in comparison to the omnivores.
Table 1. Participant characteristics by diet group (vegetarian, VEG; omnivorous, OMN) 1.
VEG
OMN
p
Measure
Male (14)
Female (13)
Male (26)
Female (17)
Age, year
36.1 ± 10.2
36.7 ± 7.7
38.0 ± 10.0
37.1 ± 8.7
0.608
Body mass, kg
73.3 ± 14.8
58.3 ± 7.6 **
78.0 ± 11.0
65.4 ± 11.6
0.043
BMI, kg/m2
24.0 ± 4.4
21.8 ± 2.5
24.8 ± 2.6
23.5 ± 3.8
0.123
Lean mass, kg
56.3 ± 7.4
42.0 ± 4.9 **
60.2 ± 7.3
45.4 ± 5.1
0.026
Waist, cm
81.6 ± 10.7
69.0 ± 14.8
85.2 ± 7.4
73.8 ± 8.2
0.093
Body fat, %
19.2 ± 6.5
25.5 ± 4.2
19.2 ± 6.4
26.9 ± 8.1
0.659
Visceral fat, cm3
447.4 ± 419.8
110.4 ± 123.0
538.5 ± 404.3
206.4 ± 254.6
0.656
METS, kcal·kg−1·week−1
108.8 ± 32.9
106.1 ± 36.6 **
91.7 ± 33.2
85.6 ± 20.8
0.018
VO2 max, mL/kg/min
62.6 ± 15.4
53.0 ± 6.9 *
55.7 ± 8.4
47.1 ± 8.6
0.011
VO2 max, L/min
4.44 ± 0.81
3.21 ± 0.67
4.29 ± 0.59
3.03 ± 0.49
0.295
Peak torque, ft-lbs
114.4 ± 26.2
65.5 ± 12.8
124.2 ± 24.5
73.6 ± 18.6
0.104
1 Data are the mean ± SD; n in parentheses; gender distribution did not differ by diet group (p = 0.460;
Chi Square analysis). p for 2-way ANOVA analyses by diet (non-normal data transformed prior to analysis
(visceral fat)). The single asterisk (*) indicates signiﬁcant difference within gender by diet group (p < 0.05);
the double asterisk (**) indicates a trend for difference within gender by diet group (0.05 < p < 0.10).
Table 2. Nutrient differences by diet group (vegetarian, VEG; omnivorous, OMN) 1.
VEG (22)
OMN (35)
p
Reference Range 2
Total kilocalories (kcal)
2443 ± 535
2266 ± 612
0.072
-
Carbohydrate (CHO) (g)
328 ± 70
248 ± 101
0.001
-
CHO (% energy)
53 ± 6
48 ± 7
0.010
45%–65%
Fiber (g)
38 ± 13
24 ± 9
<0.001
38/25 g [M/F]
Protein (g)
78 ± 19
101 ± 35
0.006
-
Protein (% energy)
12 ± 2
17 ± 4
<0.001
10%–35%
Protein (g/kg body mass)
1.2 ± 0.3
1.4 ± 0.5
0.220
0.8 g/kg
Fat (g)
90 ± 26
83 ± 33
0.901
-
Fat (% energy)
32 ± 5
32 ± 6
0.952
20%–35%
Saturated fat (g)
22.8 ± 11.2
25.7 ± 10.1
0.207
-
Saturated fat (% energy)
8.3 ± 3.1
11.6 ± 6.3
0.002
<10%
Cholesterol (mg)
102.8 ± 119.5
301.2 ± 165.6
<0.001
-
Vitamin C (mg)
117.0 ± 64.0
83.0 ± 46.5
0.076
90/75 mg [M/F]
Vitamin D (IU)
115.4 ± 111.4
129.0 ± 115.5
0.201
600 IU
Vitamin B12 (mcg)
3.0 ± 3
4.8 ± 4.6
0.006
2.4 mcg
Selenium (mcg)
41.8 ± 36.0
62.6 ± 33.6
0.002
55 mcg
Sodium (mg)
2931.2 ± 783.1
2972.8 ± 887.5
0.794
<2300 mg
Iron (mg)
19.4 ± 7.8
15.4 ± 5.4
0.017
8/18 mg [M/F]
Zinc (mg)
8.5 ± 9.1
8.9 ± 4.9
0.149
11/8 mg [M/F]
Calcium (mg)
971.0 ± 401.6
878.1 ± 314.9
0.378
1000 mg
Phosphorus (mg)
782.0 ± 378.0
831.2 ± 336.4
0.507
700 mg
Omega-3 fatty acid (g)
1.6 ± 2.5
0.9 ± 0.7
0.326
-
Omega-3 fatty acid (% energy)
0.004 ± 0.005
0.004 ± 0.003
0.613
0.6%–1.2%
Omega-6 fatty acid (g)
7.7 ± 5.4
6.1 ± 4.4
0.145
-
Omega-6 fatty acid (% energy)
2.8 ± 1.6
2.4 ± 1.3
0.358
5%–10%
1 Data are the mean ± SD; sample size in parentheses. p for general linear model analyses (non-normal data
transformed prior to analysis (all variables except carbohydrate variables and fat percentage) and 2 outliers
(VEG group) removed prior to analysis for saturated fat); 2 Reference ranges are the Recommended Dietary
Allowance or the Acceptable Macronutrient Distribution Range; note the American College of Sports Medicine
recommends that athletes consume 1.2–2.0 g protein/kg body mass.
4. Discussion
Results from this study indicate that compared to their omnivore counterparts, vegetarian
endurance athletes have comparable strength as indicated by leg extension peak torque, and possibly
a greater degree of aerobic capacity, particularly in females, as indicted by a progressive maximal
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treadmill test to exhaustion. Dietary intake on several key nutrients differed considerably between
groups. Some, but not all, results are consistent with previous reports.
Our study is signiﬁcant for its increased rigor in measurement assessments compared to previous
comparisons of vegetarian and omnivore athletes. We determined maximal oxygen uptake by a
graded test to exhaustion on a treadmill instead of predicting VO2 max using a cycle ergometer,
as recommended by Shepard and colleagues [32]. Additionally, we measured body composition
using a DXA scan, currently regarded as the clinical gold standard for body composition assessment,
instead of skinfolds [33]. Finally, we assessed both athletic performance and nutrient intake differences
between vegetarians and omnivores, whereas most previously published studies focus exclusively on
one of these areas.
4.1. Body Mass and BMI
Like other studies of vegetarians in the general population, vegetarian participants in the present
study had signiﬁcantly lower body mass compared to omnivores [10,34]. This is in spite of the fact
that our study included participants engaged in considerable endurance activities, which could be
very different in multiple ways from the general population. One prior study in athletes, conducted
by Hanne et al. compared vegetarians and omnivores anthropometrically and found no signiﬁcant
differences between groups for weight [27]. It is noteworthy that the athletes in the Hanne et al. study
included football, basketball, and water polo players in addition to endurance athletes.
4.2. Lean Body Mass
LBM was signiﬁcantly lower for the vegetarian athletes compared to their omnivore counterparts,
a difference which was most prominent among the female participants with female vegetarian athletes
possessing 7% less LBM as compared to the female omnivore athletes. In spite of this, there were no
signiﬁcant differences in body fat percentage or BMI between groups. To our knowledge, this is the
ﬁrst study to examine lean body mass differences between vegetarian and omnivore athletes. It is
important to note, however, that this difference in lean body mass did not translate into differential
peak torque on the leg extension.
Although other studies have not assessed lean body mass of vegetarian athletes speciﬁcally,
Campbell and colleagues compared resistance-training induced changes in lean body mass and
strength between groups assigned to either an omnivorous diet or a lacto-ovo-vegetarian diet for the
duration of the study and found that, in spite of differential lean body mass gains, the two groups
increased strength similarly [21]. Conversely, a 12-week training study by Haub and colleagues showed
no signiﬁcant differences in strength, body composition, or muscle cross-sectional area between groups
assigned to either a lacto-ovo-vegetarian or beef-containing diet.
4.3. Body Fat Percent and Visceral Adipose Tissue (VAT)
Contrary to the female vegetarian athletes in Hanne’s group, no signiﬁcant differences in body
fat percentage were found between vegetarian and omnivore athletes in this study. Additionally,
there were no signiﬁcant differences between groups for visceral adipose tissue (VAT). Participants
in the present study had VAT values above those reported for similar aged healthy lean sedentary
adults (~250 cm3), both omnivores and vegetarians [35,36], but lower than those noted for older
adults (1000–1560 cm3) [37]. Although there are no standard reference ranges for VAT, values near
1000 cm3 were associated with BMI values near 25 kg/m2 and values > 300 cm3 have been suggested
as predictive of risk for metabolic syndrome in young adults [36,37]. As technology permitting
quantiﬁcation of visceral adipose tissue is relatively new for research purposes, this study contributes
to the emerging literature by providing VAT values for athletes. VAT and BMI is strongly correlated
in this study (p = 0.742), a factor that may be important for estimating VAT inexpensively without a
DXA scan.
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4.4. VO2 Max
Unlike athletes in Hanne’s study, vegetarians in the present study had signiﬁcantly higher
maximal oxygen uptake than their omnivore counterparts [27]. This difference was most predominant
in the female participants with a 13% greater VO2 max score for the female vegetarians as compared
to the female omnivores, but this difference was not observed for absolute VO2 max (L/min),
which suggests that body weight factored into this difference. This gender difference is intriguing and
merits further investigation in future studies. One potential reason that athletes in the present study
had higher VO2 max values than those in Hanne’s study may be due to the difference between cycle
ergometry and treadmill testing methods. However, it is possible that the athletes in our study simply
were more trained and that diet effects on differences in VO2 potential emerge only at higher levels
of ﬁtness.
Other work that contributes to our understanding of aerobic and anaerobic performance
differences by diet include the study of Hietavala et al. that found no signiﬁcant difference in time
to exhaustion (albeit a higher oxygen uptake at a given percent of maximal oxygen consumption)
between participants following a low-protein vegetarian diet compared to a mixed diet [38]. Subjects
in this study adhered to the low protein vegetarian diet (0.80 ± 0.11 g of protein per kilogram of body
mass (g/kg) vs. 1.59 ± 0.28 g/kg on their normal diet) for four days before being tested on a cycle
ergometer. As this study did not use participants who practiced vegetarianism outside of the study,
and the amount of protein that subjects were allowed to consume on the vegetarian diet was restricted,
true differences between vegetarians and omnivores may not be evident. Baguet et al. found no
differences in repeated sprint ability between participants following a vegetarian or mixed diet for ﬁve
weeks; again, these subjects were not following a vegetarian diet long-term [26]. Raben et al. found no
differences in maximal oxygen uptake among subjects after adoption of a lacto-ovo vegetarian diet for
six weeks [25]. However, the major disadvantage of interpreting results of these studies for vegetarian
athletes is that participants in these studies only adhered to a vegetarian diet brieﬂy for the duration of
the study.
4.5. Peak Torque
Similar to the Hanne et al. study that compared the power output of vegetarian and omnivore
athletes [27], we found no signiﬁcant differences by diet in terms of peak torque using leg extensions.
Other studies in untrained older men that have examined strength development over time in response
to a training program have found mixed results when comparing participants following a vegetarian
or mixed diet [21,24]. This is noteworthy, particularly since strength and lean body mass were strongly
correlated (r = 0.764) in the present study, as well as the fact that omnivores had signiﬁcantly more
lean body mass vs. the vegetarians. A nonsigniﬁcant trend for omnivores to produce higher peak
torque is observed, however. It is conceivable that the omnivore diet pattern may be preferred for
sports that rely on greater lean mass, and subsequently peak torque. To further investigate this, future
work ought to examine if strength can be increased similarly by vegetarian and omnivore athletes
engaged in strength training (not just by participants following a vegetarian diet for a few weeks).
4.6. Nutrient Intake
Nutrient intake was calculated from food and beverage intakes only and did not include any
supplements. There were no signiﬁcant differences in caloric intake or total fat intake between
vegetarians and omnivores. However, vegetarians reported signiﬁcantly more dietary carbohydrate
(both in terms of absolute intake and as a percent of daily calories), ﬁber, and iron intake. Omnivores
consumed more dietary protein (both in terms of absolute intake and as a percent of daily calories),
saturated fat, cholesterol, and vitamin B12. However, when expressed relative to body mass, there
were no differences in dietary protein intake.
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That vegetarians and omnivores in the present study did not differ in terms of caloric intake is
consistent with ﬁndings by Janelle and Barr from their comparison of 45 vegetarian and omnivore
women [16], yet it is in contrast to results from Calkins and colleagues who compared 50 vegetarian,
vegan, and omnivores. They found vegetarians consumed about 200 fewer kcal than omnivores [19].
These studies were both in the general population, not speciﬁcally with athletes. Calkins et al. also
reported that omnivores consumed more fat than vegetarians, a fact that partially contributed to the
higher caloric intake. This too is in contrast to the ﬁndings in the present study which found no
signiﬁcant difference either in grams of fat consumed or the percent contribution of fat to the daily
calorie intake, even though saturated fat was signiﬁcantly higher in omnivorous diets. Other studies
involving the general population have also reported omnivores eating more energy and total fat than
vegetarians [10,39–41].
Higher carbohydrate (when expressed either as an absolute amount or as a percent of total daily
calories) and ﬁber intake among vegetarians in comparison to omnivores in the present study is
consistent with ﬁndings in other studies [10,39,41–44]. As these studies have been conducted in the
general population, the present study contributes to the literature by demonstrating that this dietary
pattern can be extended to endurance athletes as well. One study by Janelle and Barr stands in contrast
to these ﬁndings, as they did not ﬁnd signiﬁcant differences in carbohydrate or ﬁber intake between
vegetarian and omnivore women; those participants were not athletes [16]. That vegetarians in the
present study consumed more carbohydrates than omnivores is notable since they are all athletes,
and the importance of carbohydrates for exercise is well-established [45–47].
Like the present study, other studies have also reported that vegetarians consume less protein
(both absolute intake and as a percent of the daily calories) [10,16,39,42] and vitamin B12 [40,48]
than omnivores. Our study contributes to the literature since other reports have been in the general
population instead of within athletic groups. Of note, though, differences in dietary protein intake
are not signiﬁcant when expressed relative to body mass, which is typically the preferred method for
recommending protein for athletes [47]. Nonetheless, dietary protein intake was weakly correlated
with peak torque (r = 0.359, p = 0.006) in the present study, and dietary protein intake was moderately
correlated with lean body mass (r = 0.415, p = 0.001). Expectantly, lean body mass was strongly
correlated with peak torque (r = 0.764, p < 0.001). Hence, it is conceivable that protein intake could
inﬂuence strength if intakes had been inadequate. In the present evaluation, protein intakes in the
vegetarian participants averaged 1.2 g/kg body mass, which falls in the recommended range for
athletes [47,49].
There are conﬂicting ﬁndings in the rest of the literature regarding whether omnivores or
vegetarians consume more iron. The Wilson et al. study of vegetarian men found that vegetarians
consumed more iron [41], but Ball and Bartlett reported no difference in dietary iron intake
between female vegetarian and omnivores [50]. Clary et al. compared 1475 vegans, vegetarians,
semi-vegetarians, pescetarians, and omnivores and also showed that vegetarians consume more iron
than omnivores [39]. Although vegetarians consumed more iron than omnivores in the present study,
iron bioavailability was likely reduced as has been shown in other trials [17]. Dietary intakes of zinc
did not vary by diet group herein, but generally the literature suggests that vegetarians consume
somewhat less dietary zinc than omnivores [16,51–53]. The lower intakes of selenium by vegetarians
in comparison to omnivores has also been reported by others and reﬂects the low levels of selenium in
plant foods relative to ﬂesh foods [54,55].
4.7. Limitations
In addition to the small sample size, limitations to the study include the variable level of experience
of the athletes for their respective sports, and related ﬁtness levels. Although most participants were
training for and competing in races such as marathons, Ironman-distance triathlons, and competitive
cycling, there were a few participants who were training for shorter distance races.
However,
this variation makes results more generalizable to athletes of various ﬁtness levels.
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4.8. Future Directions
Future work is needed to compare vegetarian and omnivore endurance athletes’ performance on
events more similar to actual sporting events (such as time trials or peak power on a cycle ergometer)
and probe differences by type of vegetarian diet (lacto-ovo vegetarian or vegan). Additional work is
needed to explore the adequacy of long-term adherence to vegetarian and vegan diets for supporting
development of lean body mass.
5. Conclusions
Our cross-sectional comparison of vegetarian and omnivore adult endurance athletes shows
higher maximal oxygen uptake values among vegetarians and comparable strength, in spite of
anthropometric and dietary differences.
This study suggests that following a vegetarian diet
may adequately support strength and cardiorespiratory ﬁtness development, and may even be
advantageous for supporting cardiorespiratory ﬁtness. Certainly many factors affect an athlete’s
sports performance, and there is no dietary substitute for quality training. However, our study
contributes to the literature about cardiorespiratory and strength comparisons between vegetarian
and omnivore endurance athletes, and may provide a rationale about the adequacy of vegetarian
diets for sport performance. As this was a small cross-sectional study using endurance athletes,
larger intervention trials are necessary to bolster conclusions about adequacy of vegetarian diets to
support performance in strength and power-focused sports.
Acknowledgments: This study was supported by a grant through the Graduate and Professional Student
Association (GPSA) at Arizona State University.
Author Contributions: H.M.L. and C.S.J. conceived and designed the experiments; H.M.L. performed the
experiments; H.M.L. and C.S.J. analyzed the data; H.M.L., C.S.J., and C.M.W. wrote the paper.
Conﬂicts of Interest: The authors declare no conﬂict of interest. The funding sponsor had no role in the design of
the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision
to publish the results.
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© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).

Cardiorespiratory Fitness and Peak Torque Differences between Vegetarian and Omnivore Endurance Athletes: A Cross-Sectional Study.
Lynch, Heidi M,Wharton, Christopher M,Johnston, Carol S