A High Protein Diet Has No Harmful Effects: A One-Year Crossover Study in Resistance-Trained Males

Abstract

The purpose of this investigation was to determine the effects of a high protein diet over a one-year period. Fourteen healthy resistance-trained men completed the study (mean ± SD; age 26.3±3.9 yr; height 178.5±8.4 cm; and average years of training 8.9±3.4 yr). In a randomized crossover design, subjects consumed their habitual or normal diet for 2 months and 4 months and alternated that with a higher protein diet (>3 g/kg/d) for 2 months and 4 months. Thus, on average, each subject was on their normal diet for 6 months and a higher protein diet for 6 months. Body composition was assessed via the Bod Pod ® . Each subject provided approximately 100–168 daily dietary self-reports. During the subjects’ normal eating phase, they consumed (mean ± SD) 29.94±5.65 kcals/kg/day and 2.51±0.69 g/kg/day of protein. This significantly increased ( p<0.05 ) during the high protein phase to 34.37±5.88 kcals/kg/day and 3.32±0.87 g/kg/day of protein. Our investigation discovered that, in resistance-trained men that consumed a high protein diet (~2.51–3.32 g/kg/d) for one year, there were no harmful effects on measures of blood lipids as well as liver and kidney function. In addition, despite the total increase in energy intake during the high protein phase, subjects did not experience an increase in fat mass.

Full text

Research Article
A High Protein Diet Has No Harmful Effects: A One-Year
Crossover Study in Resistance-Trained Males
Jose Antonio, Anya Ellerbroek, Tobin Silver, Leonel Vargas, Armando Tamayo,
Richard Buehn, and Corey A. Peacock
Exercise and Sport Science Laboratory, Nova Southeastern University, Davie, FL, USA
Correspondence should be addressed to Jose Antonio; ja@nova.edu
Received  July ; Accepted  September 
Academic Editor: Michael B. Zemel
Copyright ©  Jose Antonio et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
e purpose of this investigation was to determine the eects of a high protein diet over a one-year period. Fourteen healthy
resistance-trained men completed the study (mean ±SD; age 26.3 ± 3.9yr; height 178.5 ± 8.4 cm; and average years of training
8.9 ± 3.4 yr). In a randomized crossover design, subjects consumed their habitual or normal diet for  months and  months and
alternated that with a higher protein diet (> g/kg/d) for  months and  months. us, on average, each subject was on their
normal diet for  months and a higher protein diet for  months. Body composition was assessed via the Bod Pod.Eachsubject
provided approximately – daily dietary self-reports. During the subjects’ normal eating phase, they consumed (mean ±SD)
29.94 ± 5.65 kcals/kg/day and 2.51 ± 0.69 g/kg/day of protein. is signicantly increased (𝑝 < 0.05) during the high protein phase
to 34.37 ± 5.88 kcals/kg/day and 3.32 ± 0.87g/kg/day of protein. Our investigation discovered that, in resistance-trained men that
consumed a high protein diet (∼.–. g/kg/d) for one year, there were no harmfuleectsonmeasuresofbloodlipidsaswellas
liver and kidney function. In addition, despite the total increase in energy intake during the high protein phase, subjects did not
experience an increase in fat mass.
1. Introduction
It has been postulated that the consumption of a high protein
diet may cause harmful eects, particularly in the kidneys.
Approximately a century ago, investigators found “at least
some or very severe” renal damage in a small group of rats on
a high protein diet in which one kidney had been removed [].
Other work on rodents found no evidence of renal damage;
however, they did nd that rats receiving a high protein diet
experienced renal hypertrophy []. Notwithstanding, a more
recent rat study reported that  days of very high whey pro-
tein supplemented diet (i.e.,  human-equivalent  g doses
per day) did not adversely aect blood and/or histological
markers of liver or kidney health and instead may improve
liver health when compared to rats not receiving protein [].
e challenge with determining the eects of high protein
diets on measures of health is the lack of agreement with
what constitutes a “high” intake of protein. At least in athletic
populations, the International Society of Sports Nutrition’s
position stand on protein states that “protein intakes of
.–. g/kg/day for physically active individuals is not only
safe, but may improve the training adaptations to exercise
training” []. Furthermore, scientists have used dierent
denitions of “high” protein intakes. For instance, protein
intakes greater than -% of total energy, as high as %
of total calories, or intakes that exceed the RDA have been
postulated as reaching the threshold of what constitutes a
“high protein” diet []. We would posit that basing a diet on
percentages is misleading. at is, if one were to consume a
hypoenergetic diet of  kcal in which % of the calories
were derived from protein, then that would amount to a
paltry . grams of protein. Instead, high protein diets should
always be dened as the amount of protein consumed per
unit body weight. It is our contention that high protein diets
should necessarily exceed . g/kg/d. Previous work from our
laboratory discovered that an eight-week period of heavy
resistance training coupled with high protein consumption
(>. g/kg/d) results in improvements in body composition
[]. Furthermore, at least in the short term, high protein
Hindawi Publishing Corporation
Journal of Nutrition and Metabolism
Volume 2016, Article ID 9104792, 5 pages
http://dx.doi.org/10.1155/2016/9104792

Journal of Nutrition and Metabolism
intakes had no harmful side eects [, ]. However, long-term
longitudinal data are lacking in terms of the eects of high
protein diets. us, the purpose of this investigation was to
examine the eects of high protein consumption in a group
of resistance-trained young males over a -year period.
2. Methods and Materials
2.1. Participants. Fourteen resistance-trained male subjects
volunteered for this investigation (racial/ethnic background:
 white males,  black males, and  Pacic Islander). Subjects
took part in a randomized crossover trial in which they
consumed their habitual (i.e., normal protein) or high protein
diet for two months and four months, respectively. e order
in which they consumed their normal or high protein intakes
was randomized. Subjects followed their normal and high
protein intake phases for a total of  months, respectively.
Subjects came to the laboratory on ve occasions. ey
weretestedatbaselineandthensubsequentlyaertwo-
month periods and two -month periods of following the
respective diet. e extra protein consumed by each subject
was obtained primarily from whey protein powder, which was
provided to each subject at no cost (DymatizeISO- with
 grams of protein,  gram of carbohydrate, and zero grams
of fat per serving of one scoop). However, subjects did not
have to consume the extra protein as powder; instead, they
could consume whatever extra protein source they preferred.
Nova Southeastern University’s Human Subjects Institutional
Review Board in accordance with the Helsinki Declaration
approved this study and written informed consent was
obtained prior to participation.
2.2. Food Diary. Subjects kept a diary (i.e., three days per
weekforoneyear)oftheirfoodintakeviaasmartphone
app (MyFitnessPal) equaling ∼ daily food logs over the
treatment period. e use of mobile apps for dietary self-
reporting has been previously used [–]. Every subject had
previous experience with this mobile app. e MyFitnessPal
app is a database comprised of over  million foods that
have been provided by users via entering data manually
or by scanning the bar code on packaged goods. us,
the data themselves are primarily derived from food labels
(i.e., nutrition facts panel) derived from the USDA National
Nutrient database.
2.3. Body Composition. Height was measured using standard
anthropometry and total body weight was measured using
a calibrated scale. Body composition was assessed by whole
body densitometry using air displacement via the Bod Pod
(COSMED USA, Concord, CA). All testing was performed
in accordance with the manufacturer’s instructions. Subjects
were instructed to come into the lab aer a -hour fast and no
exercise  hours prior to assessment. ey voided prior to
testing. Subjects were tested while wearing only tight tting
clothing (swimsuit or undergarments) and an acrylic swim
cap. Subjects were instructed to wear the same clothing for
all testing. oracic gas volume was estimated for all subjects
using a predictive equation integral to the Bod Pod soware.
T : Body composition and training volume.
Baseline Normal High
Weight kg . ±. . ±. . ±.
Fat mass kg . ±. . ±. . ±.
FFM kg . ±. . ±. . ±.
% body fat . ±. . ±. . ±.
Volu m e l o a d ∗,  ±, , ±, , ±
Data are mean ±SD. ere were no signicant dierences between groups.
∗Volume load is equal to the mean total amount of weight lied (kg) each
week.
Each subject was tested at least twice per visit. Data from
the Bod Pod include body weight, percent body fat, fat-free
mass, and fat mass. All testing was done with each subject
at approximately the same time of day for each of the ve
testing sessions. Although hydration status was not assessed,
eachsubjectwastestedinanidenticalmannerthroughoutthe
investigation. e Bod Pod was calibrated the morning of the
testing session as well as between each subject.
2.4. Blood Analysis: Comprehensive Metabolic Panel and Blood
Lipids. Subjects presented in a fasted state at a local Quest
Diagnosticsfacilityonveseparateoccasions.Ablood
lipid and comprehensive metabolic panel was done. is
includes the following measures: glucose, blood urea nitrogen
(BUN), creatinine, glomerular ltration rate, BUN/creatinine
ratio, sodium, potassium, chloride, carbon dioxide, calcium,
total protein, albumin, globulin, albumin/globulin ratio, total
bilirubin, alkaline phosphatase, alanine transaminase, aspar-
tate transaminase, total cholesterol, high-density lipoprotein
cholesterol, triglycerides, low-density lipoprotein cholesterol,
and the total cholesterol to high-density lipoprotein choles-
terol ratio. Quest Diagnostics performed each test according
to the standard operating procedure of the company.
2.5. Training Program. Each subject followed their own
strength and conditioning program. e investigators were in
regular contact with each subject to ensure that each subject
completed a training log. e volume load (i.e., total weight
lied per week) was determined for each treatment period.
2.6. Statistics. A -way analysis of variance (ANOVA) was
used to analyze the data with 𝑝 < 0.05 considered as
signicant. e data that were compared were baseline and
the mean of the normal treatment period [combined -
month and -month treatment] as well as the mean of the
high protein treatment period [combined -month and -
month treatment]. Data are expressed as the mean ±SD. e
statistical analysis was completed using Prism  GraphPad
Soware (La Jolla, California).
3. Results
e data for body composition are shown in Table . e
data for nutritional intake are shown in Table . Subjects
consumed more absolute and relative calories and protein

Journal of Nutrition and Metabolism 
T : Dietary intake.
Baseline Normal High
Kcal  ±  ±  ±∗
CHO g  ±  ±  ±
PRO g  ±  ±  ±∗
Fat g  ±  ±  ±
Kcal/kg/d . ±.     .   ±. . ±.∗
CHO g/kg/d . ±. . ±. . ±.
PRO g/kg/d . ±. . ±. . ±.∗
Fat g/kg/d . ±. . ±. . ±.
Cholesterol mg  ±  ±  ±
Sodium mg  ±  ±  ±
Sugars g  ±  ±  ±
Fiber g  ±  ±  ±
Data aremean ±SD. ∗Signicant dierence (baseline versus hi gh and normal
versus high; 𝑝 < 0.05).
CHO: carbohydrate, d: day, g: gram, kcal: calorie, kg: kilogram, and PRO:
protein.
during the high protein phase (𝑝 < 0.05). ere were no
signicant dierences between the normal and high groups
in any measure of health or body composition (Tables  and
).Itshouldbenotedthatonesubjectcompletedmonths
on the high protein phase and only  months on the normal
proteinphase.Hedidnotcompletethenalmonthsofthe
normal protein phase due to geographic relocation. us, for
this particular subject, we compared the mean of his normal
( months of data) and high protein phases ( months of
data).
4. Discussion
isistherstrandomizedcontrolledtrialthathasexam-
ined the eects of a high protein diet in resistance-trained
subjects over a -year treatment period. In brief, we found
no deleterious eects of a high protein diet (.–. g/kg/d)
over a -year period. Prior work from our lab has shown
that consuming a high protein diet in the short term has no
harmful eects on any clinical measure (i.e., blood lipids and
comprehensive metabolic panel) [, ].
e subjects in the current investigation alternated
between their normal or habitual protein intake and a high
protein intake. It should be noted however that even their
normal protein intake would be considered high by other
investigators [, , ]. us, our study does not support the
notion that protein intakes - times greater than the current
RDA cause any harmful eects.
Moreover, the amount of dietary ber consumed by our
subjects was ∼gramsperday.isisincontrastwiththe
average ber intake in the United States of ∼ grams per
day []. us, it is a falsehood to promote the idea that high
protein diets are mutually exclusive with a diet that is also
high in ber. Our subjects showed no harmful eects of a
hyperenergetic, high protein diet and this (i.e., blood lipids,
renal and hepatic function, etc.) may have been due partially
totheirberintake.Itisknownthathigherberintakes
are associated with a lower risk of cardiovascular disease,
cancer, and all-cause mortality [–]. On the other hand,
the cholesterol intake of our subjects was twice as high as the
typical recommendation of mg per day []. e notion
that high cholesterol intakes have a deleterious eect on blood
lipid markers of cardiovascular disease is not supported by
our data.
Prior work from our laboratory has shown that consum-
ing protein (.–.g/kg/d) in amounts that are - times
greater than the RDA results in a similar FFM increase
forboththenormalandhighproteingroups[];however,
the high protein group lost more fat mass compared to the
normal protein group in spite of the fact that they consumed
on average ∼ kcals more per day over the treatment
period. is is in contrast with the current study that showed
no change in body composition. e primary dierence
between the current study and the aforementioned one is
that subjects in the current study did not purposely alter
their training program. On the other hand, subjects in our
previous study were subjected to a dierent training stimulus
(i.e., periodized resistance-training program) than they had
been accustomed to. Inasmuch as the focus on our current
work was on the markers of health, subjects in the current
study were instructed to not alter their training regimen. An
examination of their volume load shows indeed that they did
not make any signicant alterations in training volume. us,
one would speculate that, without signicant changes in the
training stimulus, the mere provision of extra protein would
likely not lead to changes in body composition. Conversely,
the mere addition of extra protein calories also will not lead
to gains in fat mass.
4.1. Limitations. One might speculate that a limitation of
this investigation is that the subjects were young males who
had several years of resistance-training experience and were
regularly consuming a high protein diet at baseline. However,
the fact that they increased their protein intake by ∼%
and still had no deleterious side eects is further evidence
that a high protein diet in exercise-trained individuals is
indeed safe. e small sample size may also preclude one
from applying the results from this study to other populations
(i.e., sedentary men or women). Nonetheless, we would posit
that the only populations that would consume a high protein
diet are athletes (e.g., highly trained endurance and strength-
power athletes). us, the need to apply our data to other
populations may be a moot point.
5. Conclusions
In male subjects with several years of experience with
resistance training, chronic consumption of a diet high in
protein had no harmful eects on any measures of health.
Furthermore, there was no change in body weight, fat mass,
or lean body mass despite eating more total calories and
protein. Contrary to popular belief, the consumption of a
high protein diet is not mutually exclusive with a diet high
in ber nor does the consumption of cholesterol above the
standard recommendations result in any untoward eects on

Journal of Nutrition and Metabolism
T : Blood lipids.
Baseline Normal High Reference range
Total cho l e s t e r o l mg/d L  ±  ±  ± –
HDL-C mg/dL  ±  ±  ± >or = 
TG mg/dL  ±  ±  ± <
LDL-C mg/dL  ±  ±  ± <
Cholesterol/HDL-C ratio . ±. . ±. . ±. <or = .
Data are mean ±SD. ere were no signicant dierences between groups. C: cholesterol, dL: deciliter, HDL: high-density lipoprotein, LDL: low-density
lipoprotein, mg: milligram, and TG: triglycerides.
T : Comprehensive metabolic panel.
Baseline Normal High Reference range
Glucose mg/dL   ±  ±  ±–
BUN mg/dL  ±±±–
Creatinine mg/dL . ±. . ±. . ±. .–.
eGFR  ±  ±  ± 
BUN/creatinine ratio  ±±±–
Sodium mmol/L  ±±±–
Potassium mmol/L . ±. . ±. . ±. .–.
Chloride mmol/L  ±.  ±.  ±. –
CO2mmol/L  ±±±–
Calcium mg/dL . ±. . ±. . ±. .–.
Total protein g/dL . ±. . ±. . ±. .–.
Albumin g/dL . ±. . ±. . ±. .–.
Globulin g/dL . ±. . ±. . ±. .–.
Alb/Glob ratio . ±. . ±. . ±. .–.
Total Bili mg/dL . ±. . ±. . ±. .–.
Alkaline phosphatase U/L  ±  ±  ± –
AST U/L  ±±± –
ALT U/L  ±  ±± –
Data are mean ±SD. ere were no signicant dierences between groups. Alb: albumin, ALT: alanine transaminase, AST: aspartate transaminase, Bili:
bilirubin, BUN: blood urea nitrogen, eGFR: estimated glomerular ltration rate, g: grams, Glob: globulin, mmol: millimoles, L: liter, and mg: milligrams. 
indicates a value >or =  mL/min/. m2.
blood lipids. is is the rst -year longitudinal investigation
in resistance-trained males that demonstrates the lack of
harm caused by a high protein diet.
Competing Interests
Jose Antonio Ph.D. is the CEO of the International Society of
Sports Nutrition (ISSN). Dymatize is a sponsor of the ISSN.
All other authors declare that they have no conict of interests
regarding the publication of this paper.
Acknowledgments
e authors would like to thank Dymatize for providing
protein powder.
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