Article

Vegetarian Nutrition - comparing physical performance of omnivorous and vegetarian athletes

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Background/Aims: Humans consuming a vegetarian diet have a reduced relative risk in coronary heart disease, hypertension, diabetes mellitus, obesity and some cancers. Regular physical activity also assists in preventing, and reducing the severity of these conditions. An association between these two factors is being acknowledged with athletes adapting their diet to optimise physical performance. This study aimed to examine the evidence for the relationship between consuming a predominately vegetarian diet and improved physical performance. Methods: A systematic literature review was undertaken using the SCOPUS database. No date parameters were set. The keywords; vegetarian* OR vegan* AND sport* OR athlete* OR training OR performance OR endurance’ were used. Included studies; (i) directly compared a vegetarian based diet to an omnivorous/mixed diet, (ii) directly assessed physical performance, not biomarkers of physical performance, (iii) did not use supplementation emulating a vegetarian diet. Reference lists were hand searched for additional studies. Results: Seven randomised controlled trials and one cross-sectional study met the inclusion criteria. No distinguished differences between vegetarian diets and omnivorous mixed diets were identified when physical performance was compared. Conclusions: Limited evidence is available to determine if consuming a predominately vegetarian diet will impact performance in athletes. Further research is warranted though the limited studies of this review did show no impact.
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212
ORIGINAL RESEARCH
International Journal of Sport Nutrition and Exercise Metabolism, 2016, 26, 212 -220
http://dx.doi.org/10.1123/ijsnem.2015-0231
© 2016 Human Kinetics, Inc.
Vegetarian and Omnivorous Nutrition—
Comparing Physical Performance
Joel C. Craddock, Yasmine C. Probst, and Gregory E. Peoples
Humans consuming vegetarian-based diets are observed to have reduced relative risk for many chronic diseases.
Similarly, regular physical activity has also been shown to assist in preventing, and reducing the severity of
these conditions. Many people, including athletes, acknowledge these ndings and are adopting a vegetarian-
based diet to improve their health status. Furthermore, athletes are incorporating this approach with the specic
aim of optimizing physical performance. To examine the evidence for the relationship between consuming a
predominately vegetarian-based diet and improved physical performance, a systematic literature review was
performed using the SCOPUS database. No date parameters were set. The keywords vegetarian OR vegan
AND sport OR athlete OR training OR performance OR endurance were used to identify relevant literature.
Included studies (i) directly compared a vegetarian-based diet to an omnivorous/mixed diet, (ii) directly assessed
physical performance, not biomarkers of physical performance, and (iii) did not use supplementation emulating
a vegetarian diet. Reference lists were hand searched for additional studies. Seven randomized controlled trials
and one cross-sectional study met the inclusion criteria. No distinguished differences between vegetarian-based
diets and omnivorous mixed diets were identied when physical performance was compared. Consuming a
predominately vegetarian-based diet did not improve nor hinder performance in athletes. However, with only
8 studies identied, with substantial variability among the studies’ experimental designs, aims and outcomes,
further research is warranted.
Keywords: vegan, veganism, vegetarianism
A range of vegetarian diets exist, all of which are
typically plant-based and are often classied on the exclu-
sion or inclusion of animal, or animal derived products.
Vegan, pesco-vegetarian, ovo-vegetarian, lacto-vegetar-
ian, and lacto-ovo-vegetarian (LOV) diets are examples of
vegetarian-based diets in which fruits, vegetables, grains,
nuts, seeds and legumes represent a high proportion of
dietary intake compared with meat and dairy products
(Venderley & Campbell, 2006). Table 1 provides an over-
view of common vegetarian diets. Reductions in coronary
heart disease, hypertension, diabetes mellitus, obesity and
even some cancers have been observed in participants
following vegetarian-based diets (Barnard et al., 2015;
Olrich & Fraser., 2014; Ornish et al.,1998; Schmidt et
al.,1997). Diets of this nature are typically higher in oligo
and polysaccharides, ber, fruits, vegetables, antioxidants
and phytochemicals while lower in saturated fat and
cholesterol compared with omnivorous diets (Venderley
& Campbell, 2006). Some athletes have adopted a veg-
etarian diet to acquire the health benets associated, but
also believe the diet may assist in achieving appropriate
carbohydrate intake, weight management and other per-
formance enhancing advantages (Fuhrman & Ferreri,
2010). Physical performance is a broad term, however,
in the context of this review will include; strength, speed,
endurance and power, while excluding other traditional
components such as balance and exibility.
Although mechanisms linking a diet high in plant-
based foods to improved physical performance are lim-
ited, there are three plausible theories described in the lit-
erature. Firstly, it has been hypothesized that a vegetarian
diet may enhance an athlete’s performance due to the high
carbohydrate intake leading to improved glycogen stores
in the body (Barr & Rideout 2004; Ferreira et al., 2006).
Secondly, the increased phytochemicals and antioxidants
consumed in vegetarian-based diets may also help reduce
oxidative stress associated with prolonged exercise and
improve general immunity (Trapp et al., 2010). Thirdly,
it is widely accepted that intramuscular acidity can limit
high-intensity exercise (Carr et al., 2011). A relationship
has been established linking oral supplements, namely
sodium bicarbonate and sodium citrate, to altered blood
alkalosis levels. When ingested these buffers have been
shown to have an ergogenic effect on high-intensity acute
exercise (Carr et al., 2011). Conversely, ingested acidic
supplements can be ergolytic. Evidence suggests consum-
ing a vegetarian diet may have an alkaline effect on acid-
base levels compared with nonvegetarians due to the high
The authors are with the School of Medicine, University of
Wollongong, Wollongong, Australia. Address author correspon-
dence to Joel Craddock at jcc256@uowmail.edu.au.
IJSNEM Vol. 26, No. 3, 2016
Vegetarian-Based Nutrition and Physical Performance 213
fruit and vegetable intake, while being lower in animal
based proteins (Hietavala et al., 2015; Deriemaeker et al.,
2010). Although a long-term vegetarian-based diet may
not have the same effect as an acute sodium bicarbonate
supplement, it is plausible, that a small ‘resetting’ change
in the homeostatic baseline may be approached when a
sustained vegetarian-based diet is followed, leading to a
potential increase in physical performance. Despite these
promising notions, there remains concern that a subopti-
mal vegetarian diet may increase risk for micronutrient
deciencies and reduce muscle creatine concentrations
leading to submaximal performance (Barr & Rideout,
2004). Studies connecting vegetarian diets to improved
health are well-established (Barnard et al., 2015; Olrich
& Fraser, 2014; Ornish et al.,1998; Schmidt et al.,1997);
however, the evidence for this phenomenon to be trans-
ferred to improved physical performance in athletes
is less clear. The aim of this study was to examine the
evidence for the relationship between consumption of a
vegetarian-based diet and improved physical performance
by conducting a systematic literature review. Due to a
vegetarian-based diet theoretically increasing muscle
glycogen, cell alkalinity, and immunity while reducing
oxidative stress, it was hypothesized that this diet may
improve physical performance in athletes.
Methods
Study Protocol
A systematic literature review (NHMRC, 2000) was
conducted in January 2015 using the SCOPUS database
with no date exclusions. The search used the following
keywords; vegetarian OR vegan AND sport OR athlete
OR training OR performance OR endurance in article,
keywords or abstract. A search for unpublished literature
was not performed though reference lists of the included
publications were examined for additional relevant stud-
ies. National Health Medical Research Council’s levels
of evidence were applied to the included studies.
Study Selection
Inclusion of studies met the following requirements. The
studies (i) directly compared a plant-based diet (e.g.,
ovo-vegetarian, LOV or vegan) to a typical omnivorous/
mixed diet, (ii) directly assessed physical performance,
not solely biomarkers of physical performance (immune
biomarkers were exempt from this inclusion criterion as
physical detection of immunity is difcult to measure).
The inclusion criterion was created to assess diet and its
effect on performance rather than other external factors
such as supplementation and lifestyle factors. It was
important for physical performance to be measured,
as biomarkers alone may not translate into effects on
physical performance. Studies that met the following
exclusion criteria were omitted: (i) studies with key words
pregnancy, nonhuman, high performance liquid chro-
matography (excluded within database search limits);
(ii) journal articles not published in English; (iii) studies
examining the relationship between diet and lifestyle fac-
tors on physical performance; (iv) published conference
papers, short surveys, letters, notes, editorials, articles in
press, book series, erratum and conference proceedings;
and (v) participants taking supplementation to emulate
a vegetarian diet.
Data extraction included information on the publica-
tion year, study design/quality, number of participants,
total sample size, population type, dropouts, intervention,
diet, study results/conclusions (Table 2). Study quality
Table 1 Classification of Dietary Patterns
Note. Adapted from “Beyond Meatless, the Health Effects of Vegan Diets: Findings from the Adventist Cohorts,” by Lee & Sabate, 2014,
Nutrients, 6, p. 2133. Copyright 2014 by the authors; licensee MDPI, Basel, Switzerland. Adapted with permission.
214 IJSNEM Vol. 26, No. 3, 2016
Table 2 Body of Evidence—Summary Table of Included Journal Articles with American Diabetes Association Quality Rating Template
Results Included
Study
Study Design
(Level of
Evidence) Population Intervention Dietary Group Study Results/Conclusion
Anaerobic and Aerobic Performance
Baguet et al.
(2011) Pseudo RCT
(Level III-1*)
n = 20
Healthy, nonvegetarian
participants.
11 males, 9 females.
5 weeks, sprint
training program
-Mixed diet
-Vegetarian Diet
(*Both groups
supplemented with
creatine).
LOV
Energy 9321kJ (P= 13.13%,
CHO = 55.08%, F = 28.00%,
EtOH = 3.79%)
Mixed
Energy 9693kJ (P = 15.78%,
CHO = 54.55%, F = 26.02%,
EtOH = 3.67%)
No performance difference in repeated sprint
ability test between LOV diet and mixed diet.
Hietavala et
al. (2012) RCT
(Level II**)
n = 9
Healthy, recreationally
active men.
No mention of prior
eating habits.
Crossover design w/
16-day washout period
4-day vegetarian diet
4-day normal diet.
Low protein vegetarian diet
Energy 1046 kJ, (P = 10.1%,
CHO = 58.7%, Fat = 24.7%
(Limited grain and dairy)
Normal Diet
Energy 11687 kJ (P = 17.6%,
CHO = 49.8%, Fat = 28.1%)
Oxygen consumption was signicantly higher at
40, 60 and 80% of maximum oxygen capacity
(cycle ergometer). Suggestive of poorer exercise
economy in vegetarian diet. No further effect on
maximal aerobic performance.
Raben et al.
(1992)^^ RCT
(Level II**)
n = 8
Endurance trained male
athletes. Nonvegetarians
before study.
Crossover design
with 4-week washout
period, 6-week LOV
diet
6-week nonvegetarian
diet.
Both diets included:
57% E Carbohydrate, 14% E Protein,
29% E Lipids
LOV
Protein composition (16% animal
derived protein, 84% vegetable protein)
Mixed Western
Protein composition (67% animal
protein, 33% vegetable protein)
No difference in maximal oxygen uptake (graded
ergometer cycle or treadmill test) or maximal
voluntary contraction (measured with strain
gauge) between groups.
Hanne et al.
(1986)
Cross- sectional
cohort
(Level III-2***)
n = 98
49 vegan, lacto vegetarian
or LOV
49 nonvegetarians.
NA
Vegetarian-based
> 2 years
(vegan, lacto vegetarian or LOV)
Mixed—Nonvegetarian-based diet
No difference in anaerobic (Wingate anaerobic
test) or maximal oxygen uptake (cycle stress test)
performance.
(continued)
215
IJSNEM Vol. 26, No. 3, 2016
Strength and Power
Haub et al.
(2005)^ RCT
(Level II**)
n = 21
Healthy men aged 59–78
BMI 24–33 kg/m2.
12-week RT program
3 days/week
LOV
0.6 g/protein/kg/day from TVP Energy
9.37MJ (P= 1.17 g/kg/day,
CHO = 274 g/day, F = 85g/day)
LOV + Beef
0.6 g/protein/kg/day from beef Energy
9.09MJ (P= 1.10 g/kg/day,
CHO = 282 g/day, F = 73g/day)
No difference in strength (repetitions until
fatigue) or power gains (1 rep max) between a
LOV diet + soy or LOV diet +Beef. No differ-
ence between groups for upper body or lower
body power output.
Campbell et
al. (1999) Pseudo RCT
(Level III-1*)
n = 19
Sedentary men (51–69
years) overweight to
moderately obese aged
12-week resistance
training program
Group 1 (Mixed Diet)
Group 2 (LOV)
LOV (self-selected)
Energy ~10.3 MJ (52% E Carbohydrate,
13% E Protein, 34% E Lipid
No difference in strength (1 Rep Max) with RT
between groups for any of the exercises
performed.
Mixed—(habitual unrestricted)
(provided 50% of total dietary protein
from meat)
Energy ~8.6 MJ (50% E Carbohydrate,
16% E Protein, 32% E Lipid
Wells et al.
(2003)^ RCT
(Level II**)
n = 21
Healthy men aged 59–78
BMI 24–33 kg/m2
12-week RT program
3 days/week
LOV
0.6 g/protein/kg/day from TVP Energy
9.37MJ (P= 1.17 g/kg/day,
CHO = 274 g/day, F = 85 g/day)
LOV + Beef
0.6 g/protein/kg/day from beef Energy
9.09MJ (P= 1.10 g/kg/day, CHO = 282
g/day, F = 73 g/day)
No differences in strength (1 rep max) between
groups in all but one exercise. Vegetarian group
had a larger increase in strength for knee
extensions (p < .01).
Immune Parameters
Richter et al.
(1991) ^^ RCT
(Level II**)
8 endurance-trained male
athletes (4 cyclists, 1
runner, 1 rower, 2 mixed)
Nonvegetarians before
the study.
Crossover design
with 4-week washout
period, 6-week LOV
diet
6-week nonvegetarian
diet
Both Diets Included:
57% E Carbohydrate, 14% E Protein,
29% E Lipids
LOV
Protein composition (16% animal
derived protein, 84% vegetable protein)
Mixed western
Protein composition (67% animal pro-
tein, 33% vegetable protein)
No difference in composition or concentration
in in-vivo function of human blood mononuclear
cells between a meat rich mixed diet, or a LOV
diet.
Note. CHO = carbohydrate, F = fat, P = protein, EtOH = alcohol, E = energy, LOV = lacto-ovo vegetarian, RCT = randomized controlled trial, RT = resistance training, TVP = textured vegetable protein.
*Pseudo RCT, Level III-I—A study of test accuracy with: an independent, blinded comparison with a valid reference standard, among nonconsecutive patients with a dened clinical presentation.
**RCT Level II—A study of test accuracy with: an independent, blinded comparison with a valid reference standard, among consecutive patients with a dened clinical presentation.
***Level III-2—A comparative study with concurrent controls: Nonrandomized, experimental trial, cohort study, case-control study, interrupted time series with a control group.
^Same experiment/data set—assessed different parameters of physical activity.
^^Same experiment /data set—assessed different parameters of physical activity.
Table 2 (continued)
IJSNEM Vol. 26, No. 3, 2016
216 Craddock, Probst, & Peoples
was assessed using the quality criteria checklist of the
Evidence Analysis Manual (http://www.andeal.org/) of
the Academy of Nutrition and Dietetics (2012). All eight
studies returned positive scores using the quality criteria
checklist of the Evidence Analysis Manual (data not
shown) of the Academy of Nutrition and Dietetics (2012).
Results
The literature search identied 327 studies of which eight
articles met the inclusion criteria.
The eight included studies were varied with respect
to population, intervention period, diet composition,
and primary objectives including attribute of physical
performance (Table 2). For instance, several papers
examined muscular power and strength (Campbell et al.,
1999; Haub et al., 2005; Wells et al., 2003), four assessed
anaerobic and aerobic performance (Baguet et al., 2011;
Hanne et al., 1986; Hietavala et al., 2012; Raben et al.,
1992) while one investigated immune parameters (Richter
et al., 1991) in relation to a vegetarian-based diet. In addi-
tion, most papers used different physical testing and/or
biomarkers. The following sections are structured accord-
ing to the type of physical performance being analyzed,
although there was some cross over between studies.
Resistance (Strength/Power) Training
Three studies examined the difference between a LOV
diet and a typical beef-containing western diet and its
effect on Resistance Training (RT) in elderly men (Camp-
bell et al., 1999; Haub et al., 2005; Wells et al., 2003).
The studies were unied regarding muscular strength.
All three studies found no signicant difference in mus-
cular strength or power between the LOV groups and the
omnivorous groups except in Wells et al. (2003) where the
LOV group displayed a signicant increase in strength
for knee extensions (p < .01), yet both groups revealed
signicant improvements in muscular strength and power.
Campbell et al. (1999) did, however, report resistance
training induced changes in whole body composition
(p = .014) and an increase in mean type II muscle ber
area size between groups (p = .005). Similarly, Wells
et al. 2003, described hemoglobin and hematocrit were
signicantly increased in the meat group (p < .01) though
this did not affect strength testing.
Anaerobic and Aerobic Performance
Four studies were identied relating a vegetarian-based
diet to either anaerobic and/or aerobic performance.
Hietavala et al. (2012) revealed that a low protein veg-
etarian diet had no signicant effect on exercise time to
exhaustion, but oxygen consumption was signicantly
higher at 40%, 60% and 80% of maximum oxygen con-
sumption compared with a mixed diet (2.03 ± 0.25 vs.
1.82 ± 0.21 L/min, p = .035; 2.86 ± 0.36 vs. 2.52 ± 0.33
l/min, p < .001 and 4.03 ± 0.50 vs. 3.54 ± 0.58 L/min, p
< .001; respectively). Venous blood pH, strong ion differ-
ence, partial pressure of CO2, HCO3-, was also measured
with no signicant difference between diets. Comparably,
Baguet et al. (2011) found that anaerobic performance
improvement (repeated sprint ability test) was not differ-
ent between the diet groups. Hanne et al. (1986) assessed
both anaerobic and aerobic capacity between vegetarian
and nonvegetarian athletes. No signicant difference in
aerobic performance, as measured by predicted maximum
oxygen consumption and rating of perceived exertion
(RPE) was observed. Likewise, no signicant differences
between groups were measured using the Wingate test to
assess anaerobic performance (Table 2).
Raben et al. (1992) reported no signicant differ-
ences between a LOV diet and maximum oxygen con-
sumption, maximal voluntary contraction, endurance per-
formance or muscle glycogen concentrations compared
with a mixed diet (both diets controlled for carbohydrate
57%, protein 14% and fat 29%). A signicant decrease in
fasting serum testosterone was observed over the 6-week
intervention period in the vegetarian groups diet (median
21.1nmol-1 to 13.7nmol-1, p < .05), where no change was
observed in the mixed diet. This did not have an effect
on any physical performance parameters.
Immune Function
Richter et al. (1991) reported that the immune parameters;
blood mononuclear cells, and natural killer cells did not
differ between a vegetarian and mixed diet after aerobic
exercise. Similarly, phytohemagglutinin (PHA) and
puried protein derivative (PPD; tuberculin) showed no
signicant differences between dietary groups.
Discussion
This review is the rst to explore an exclusive vegetarian-
based diet and its effects on physical performance using
a rigorous systematic approach. Earlier investigations
have focused on components of a vegetarian diet and
performance or supplementation emulating a vegetar-
ian diet and performance but none have examined the
diet holistically, the way individuals or athletes would
typically eat. Due to the limited evidence pool, and the
disparate outcomes of performance tested, evaluating the
association between a vegetarian-based diet and improved
physical performance in athletes was immeasurable. This
did not align with the primary hypothesis that a vegetar-
ian diet would improve physical performance in athletes.
Nieman (1998) similarly reviewed vegetarian diets
and possible links to improved physical performance.
Seventeen scientic papers were assessed by Nieman
before 1998, with neither a benecial nor a detrimental
effect reported. Of the eight papers, which were reviewed
in this investigation, all were unied with Neiman’s
ndings. The vegetarian-based diet did not improve nor
hinder physical performance. It is noteworthy to declare
that all references used in Nieman’s 1998 paper were
hand searched for inclusion in this systematic review.
No additional articles were included. Nieman’s study
was not extracted in the methodology, and therefore not
IJSNEM Vol. 26, No. 3, 2016
Vegetarian-Based Nutrition and Physical Performance 217
included in the results of the review. This occurred due
to the keywords used by Nieman (exercise, endurance,
athlete, carbohydrate, meat, iron, protein, creatine, veg-
etarian diet, humans) being broad with more focus on
food groups and macronutrients.
Due to limited studies and dissimilar performance
measurements, there may still be some merit to the
hypothesis forecasting a vegetarian-based diet increas-
ing performance due to increased muscle glycogen, cell
alkalinity and immunity, while reducing oxidative stress.
This is particularly true for reducing oxidative stress as
no trials were found on the subject.
Strength and Power
The three papers examining a LOV diet were unied,
identifying that both the control and LOV groups sig-
nicantly improved muscular strength and power equally
during the study period. All three studies used elderly men
as subjects concluding there was no difference between
LOV diets and omnivorous diets in resistance training
in elderly men. However, this may not be representative
of the larger population. Wider studies are required to
condently consolidate their ndings with the inclusion
of both genders, and a range of ages. In two out of the
three studies texturised vegetable protein was used fre-
quently in the LOV diets with breakfast patties, grillers,
chick[pea] patties and veggie dogs highly prominent
(Haub et al., 2005; Wells et al., 2003). Products such
as these often contain food color, pH modier, surface-
active substrates, emulsiers and surfactants (Asgar et al.,
2010). Ideally, the aim of this study was to investigate a
more whole food vegetarian-based diet. Research limit-
ing the use of texturised vegetable protein products is
warranted to more adequately align a plant-based dietary
intake, and its response to resistive training.
Figure 1 — The PRISMA owchart showing the initial and nal number of studies obtained.
IJSNEM Vol. 26, No. 3, 2016
218 Craddock, Probst, & Peoples
Anaerobic and Aerobic Performance
Four papers were identied analyzing a vegetarian diet
and its effect on endurance and/or aerobic performance.
These studies exhibited some heterogeneity with three of
the papers reporting on maximal aerobic capacity, two
papers reporting on anaerobic performance and one also
including isometric strength performance. No signicant
differences were observed between dietary intake and
physical performance.
As only four studies with small participant pools
were identied, it is imprudent to make a judgment on
the effect of a vegetarian diet regarding this type of physi-
cal performance. The studies were consistent, however,
revealing no signicant differences between dietary
groups in short, middle or endurance performance. This
should only serve as a preliminary statement with further
research required. This is particularly true with Baguet et
al. (2011) issuing both the vegetarian and nonvegetarian
groups 1 g/day of creatine monohydrate to reduce a cre-
atine deciency in the vegetarian diet group.1 Some stud-
ies, such as that of Bemben & Lamont (2005), have linked
creatine to improved anaerobic performance. Although
Baguet et al. (2011) were analyzing carnosine concen-
tration, the creatine supplementation may have skewed
the results, at least for the applicability of this review.
In the study by Baguet et al. (2011), baseline measure-
ments between vegetarians and nonvegetarians revealed
lower total creatine concentration (p < .05). If creatine
is implicated in improved performance, and vegetarians
have reduced concentrations to nonvegetarians, creatine
supplementation may be particularly inuential in per-
formance results. Supplementing with creatine eliminates
it as a variable, enabling the specic focus of carnosine;
which has been hypothesized to increase performance,
however, greatly limits the ndings to address the rela-
tionship between a vegetarian diet and performance in
short to middle distance athletes. From this study, it can
be supposed, that there is no difference in carnosine
concentrations between the two dietary groups (Baguet
et al., 2011), however, any links to physical performance
must be questioned due to the creatine supplementation.
Hietavala et al. (2012) interestingly found that although
there was no overall difference between the dietary
groups’ acid-base status or overall effect on maximum
oxygen capacity, cycling efciency decreased in the
LOV group. This would not be a desirable effect for any
athlete, which deserves to be explored further. Three of
the studies assessing anaerobic and aerobic performance
used short treatment periods of vegetarian consumption
(Baguet et al.; 5 weeks: Raben et al.; 6 weeks: Hietavala
et al.: 4 days). The only study which was included where
a vegetarian diet was adopted for an extended period of
time, was that of Hanne et al. (1986). The participants in
this study, were vegetarian for a minimum of two years.
This timeframe would be more suitable to assess meta-
bolic alterations. However, the sample size was small (39
vegetarians) and the investigation did not implement a
randomized controlled study design, but a cross sectional
assessment. A larger number of participants, longer treat-
ment times, studies without additional supplementation
and a greater number studies are needed to condently
make a conclusion about a vegetarian-based diet and its
effect on anaerobic an aerobic performance.
Immune Parameters and Performance
It has been suggested that due to the wealth of phyto-
chemicals, antioxidants and plethora of micronutrients
in vegetarian-based diets, immune function may be
improved in the vegetarian population (Nieman, 1988).
This was not observed in the single study identied
comparing immune status between the two dietary
groups (Richter et al., 1991). The treatment groups in
this particular study were subjected to a macro energy
controlled—57% Carbohydrate, 14% Protein, 29% Lipids
LOV (16% animal derived protein, 84% vegetable pro-
tein)—or mixed western diet (67% animal derived pro-
tein, 33% vegetable protein) for a total of 6 weeks. This
duration is perhaps lacking the duration for full effects
of a vegetarian/vegan diet to become apparent. A larger
body of research with an extended duration of vegetarian
consumption is needed before this can be concluded.
Mechanisms
Mechanisms other than those hypothesized to discrimi-
nate between a vegetarian-based diet and a mixed diet
were proposed in some of the studies. Raben et al. (1992)
for example hypothesized a decrease in sex serum tes-
tosterone due to a vegetarian-based diet. Raben et al.
suggested nonheme iron may not be absorbed as readily
as heme iron and increased ber intake may reduce the
bioavailability of some nutrients, causing implications
to a heavily training athlete. This was found not to be
the case as the study revealed low level sex serum hor-
mones in the vegetarian group but no changes in physical
performance.
Baguet et al. (2011) and Hietavala et al. (2012)
investigated the relationship between vegetarian-based
diets and their effect on acid-base balance. Hietavala
et al. (2012) found no signicant difference in venous
blood pH, strong ion difference or total concentration of
weak acids (Atot), suggesting a low protein, vegetarian-
based diet (Protein 10.1% ± 0.26, Carbohydrate 58.7%
± 2.4, Fat 24.7% ± 2.3) may not optimize acid-base
balance and thus improve physical performance. Baguet
et al. (2011) predominately focused on carnosine and
its buffering capacity. Lacto-ovo vegetarians revealed
lower total creatine concentration (p < .05) compared
with nonvegetarian participants, however, no difference
in performance was observed, again suggestive of a
vegetarian-based diet being ineffective at providing some
sort of buffering effect.
Limitations
A limitation with the body of evidence is that all of the
randomized controlled trials used extremely short peri-
IJSNEM Vol. 26, No. 3, 2016
Vegetarian-Based Nutrition and Physical Performance 219
ods of dietary intervention ranging from 4 days to 12
weeks. Changes in stored nutrient concentration could
take much longer than this period. For instance, a recent
study revealed that the most notable decline in vitamin
B-12 in vegan participants occurred between 24 months
and 60 months (Madry et al., 2012). The results from the
present literature review only offer understanding into
the short-term effects of a vegetarian-based diet, which
may be useful for acute purposes, such as leading into
a competition or race, however; does not address long-
term effects. This is signicant, as athletes following a
vegetarian-based diet would typically do so for extended
periods.
In addition, many of the included papers lacked infor-
mation on the standardization of dietary intake between
groups and/or lacked detail about dietary compliance.
Jeacocke and Burke (2010), note the possible impact poor
dietary control can have on the outcome of a study. This is
of particular interest in this review as the sample sizes were
small, thereby likely to exaggerate the results of inadequate
dietary standardization between groups.
While this systematic literature review has provided
new insights into the effects of vegetarian-based nutrition
and physical performance in athletes via a highly rigor-
ous and structured review, some improvements could be
made. The present SLR’s search criterion encompasses
dietary factors and effects on total physical performance.
Rened search parameters focusing on specic domains
of physical performance may uncover additional studies
within that domain. Furthermore, as limited research
was identied exploring vegetarian-based nutrition and
physical performance, including cross-sectional studies
comparing performance biomarkers may have increased
the strength of this review.
Conclusion
Currently, the evidence for consuming a predominately
vegetarian-based diet and improved athletic performance
is lacking. In the eight studies which were identied in
this review, however, the vegetarian-based diet did not
improve performance, nor did it hinder it. There appeared
to be no differences at least acutely between a vegetarian-
based diet and an omnivorous diet in muscular power,
muscular strength, anaerobic or aerobic performance.
Many limitations were identied within the body of
evidence including the total body of evidence being very
small (seven trials one cross-sectional analysis), the body
of evidence experimental outcomes varied signicantly,
typically short dietary treatment times were adminis-
tered (all but one study used treatments of 4 days to 12
weeks), resistance training focused only on elderly men
and supplementation was used in one of the trials. More
trials are needed to address the limitations and provide
stronger evidence toward vegetarian-based diets and their
effects on physical performance in athletes. It would
be recommended that future research meets high level
randomized controlled trial design with strict vegetarian-
based dietary intervention lasting 6 months or greater to
determine the association between a vegetarian-based
diet and physical performance.
Notes
1. Creatine monohydrate was used across both dietary groups
to eliminate it as a variable. As both groups supplemented with
creatine, it was included.
Acknowledgments
No funding has been received for the preparation of this manu-
script. The authors declare that there are no conicts of interest
that are directly relevant to the content of this review. The study
was designed by Joel Craddock and Yasmine Probst; data were
collected and analyzed by Joel Craddock; data interpretation
and manuscript preparation were undertaken by Joel Craddock,
Yasmine Probst and Greg Peoples. All authors approved the
nal version of the paper.
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