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SCAN’S
Pulse
Spring 2021, Vol. 41, No 2
CONTENTS CPE Article
1
CPE Article Dietary Protein Requirements and Lean Body
Dietary Protein Requirements and Lean Mass: A New Marker for Adequacy?
Body Mass: A New Marker for Adequacy?
3 by Joshua L. Hudson, PhD and Wayne W. Campbell, PhD
From the Editor
6 For the two CPE feature articles appearing intake may be needed in the elderly pop-
CPE Article in this issue, the Academy of Nutrition and ulation.
Fueling Firefighters to Promote Health Dietetics, an accredited Provider with the
and Fitness: How Sport Performance Di- Commission on Dietetic Registration (CDR), The human body requires exogenously
etitians Can Work With First-Responders has approved a total of 1 continuing pro- derived sources of amino acids to replace
fessional education unit (CPEU), level 1. To the endogenous amino acids that cannot
9 apply for freeCPE credit, go to www.scan- be synthesized in the body lost from irre-
dpg.org/nutrition-info/pulse-newsletters/ versible oxidation.1 Consequently, there
A Cooking Education Intervention to In- and click Take the Quiz Now. Upon suc- is a minimum amount of dietary protein
crease Self-Efficacy and Body Apprecia- cessful completion of the quiz, a Certificate needed to replace these essential amino
tion in Collegiate Athletes of Completion will appear in your My Pro- acids. In the United States, this minimum
13 file (under the heading, My History). The amount was estimated using nitrogen
SCAN Notables certificate may be downloaded or printed balance techniques to measure the dif-
for your records. ference between nitrogen intake and ex-
14 cretion (urine, feces, and integumental
From the Chair Learning Objectives losses); the dietary protein requirements
are considered the minimum continuing
15 After you have read this article, you will daily intake to prevent net nitrogen
be able to: loss—i.e., zero balance.1 Based on a meta-
Conference Highlights analysis of 19 nitrogen balance studies,
17 Summarize the literature on the influ- zero balance can be achieved for half of
Research Digest ences of dietary protein quantity on the healthy adult population aged 19
changes in skeletal muscle during weight years or older by consuming 0.66 g·kg-
19 stability and weight loss. 1·d-1 of good quality protein (estimated
Of Further Interest average requirement, EAR); 0.80 g·kg-1·d-
Explain what the evidence suggests 1 is the recommended dietary allowance
20 regarding adequate and optimal protein (RDA) to cover the total protein needs for
intakes for individuals participating in a 97.5% of the healthy adult population.1
Upcoming Events resistance training program.
When a person is in nitrogen balance, i.e.,
Discuss cases in which higher protein whole body excretion is equal to dietary
intake, it is assumed that normal physio- skeletal muscle could be used to define
Academy of Nutrition and Dietetics logical functions are being supported by both a minimum and optimal daily pro-
Dietetic Practice Group of Sports, the dietary protein intake. However, the tein intake recommendation. This article
Cardiovascular, and Wellness nitrogen balance technique is fraught provides a brief review of the available
Nutrition (SCAN) with methodological issues that typically literature on the adequacy of the protein
SCAN Website: www.scandpg.org overestimate nitrogen intake and under- RDA to support lean body mass during
estimate nitrogen excretion; this leads to four conditions in the context of age:
SCAN Office an artificially lower requirement value weight stability (or energy balance),
120 S. Riverside Plaza, Suite 2190 than may be needed to support biologi- weight loss, weight loss with exercise
Chicago, IL 60606 cal functions.2 Importantly, nitrogen bal- training, and exercise training.
Phone: 800/249-2875 ance-derived EAR and RDA values have
info@scandpg.org not been conclusively linked to a biologi- Weight Stability
Executive Director: Rebecca Frabizio
cally relevant endpoint.3, 4 In search of a
physiologically or morphologically rele- Current nitrogen balance-based dietary
SCAN Executive Committee vant endpoint, skeletal muscle has been protein recommendations are made
Chair proposed as one phenotypic marker to based on life stage (age, sex, pregnancy
Christine Karpinski, PhD, RD, CSSD indicate protein adequacy. status); each stage of life requires a differ-
ent relative protein intake.1 Limited ran-
Chair-Elect Skeletal muscle—a major depot for di- domized controlled-feeding research
Elizabeth Abbey, PhD, RDN, CDN etary-derived amino acids—comprises exists comparing the effect of consuming
Past Chair 40% of total body mass and constitutes the protein RDA versus a higher protein
Jennifer Ketterly, MS, RD, CSSD 25% to 30% of total body protein synthe- intake during periods without purposeful
sis.5 Functionally, skeletal muscle is re- stress (i.e., weight stability) on skeletal
Treasurer sponsible for coordinating physical muscle changes. Numerous meta-analy-
Kathleen Woolf, PhD, RD, FACSM movements. Metabolically, skeletal mus- ses of randomized controlled trials have
Secretary cle is the largest site for glucose disposal shown that higher versus lower protein
Caroline Mandel, MS, RD, CSSD and lipid oxidation; lean mass, which is diets are associated with favorable lean
predominantly skeletal muscle, is also a mass changes.6-13 However, most of these
Director, Cardiovascular Health Subunit significant predictor of overall energy ex- trials included exposures to energy re-
Geeta Sikand, MA, RDN, CDE, FNLA, FAND penditure.1 In a fasted state, skeletal mus- striction or exercise—potent catabolic
Director, Sports Performance Subunit cle serves as a functional depot of amino and anabolic stressors.
Linda Samuels, MS, RD, CSSD acids that can be used to support periph-
eral and central tissue/organ protein syn- One meta-analysis compared groups
Director, Wellness & Wellbeing thesis, gluconeogenesis, and energy consuming a higher protein diet (1.3
Mark Hoesten, RD -1 -1
production. In a fed state, dietary-derived g·kg ·d on average among groups) with
Director of Events amino acids stimulate protein synthesis groups consuming the protein RDA (0.8
-1 -1 14
Roberta Anding, MS, RD, CDE, CSSD to replete proteins catabolized in the ± 0.5 g·kg ·d ). Among five randomized
fasted state. Thus, skeletal muscle is dy- controlled trials (seven comparisons) that
Director of Communications namic and can adapt in response to did not include purposeful energy re-
Cara Harbstreet, MS, RD acute and chronic exposure to a cata- striction or exercise (Table 1), the overall
Director of Member Services bolic or anabolic stimulus, increasing or effect showed that consuming more pro-
Michelle Rockwell, RD, CSSD, CSSD decreasing in protein mass as necessary. tein than the RDA did not differentially
influence changes in lean mass
SCAN Delegate to House of Delegates Given the importance of skeletal muscle, (weighted mean difference [95%CI]; 0.08
Lynn Kam, PhD, MA, MBA, RDN studies that assess the influence of di- kg [-0.59, 0.75]). Because these studies
____________________________ etary protein quantity on changes in did not simultaneously assess both nitro-
Editor-in-Chief, SCAN’S PULSE Table 1. Summary of Meta-Analyses Results Comparing Effects of Consuming
Mark Kern, PhD, RD, CSSD
Protein RDA vs. >Protein RDA in Various Stressed States
DPG Relations Manager
Tresha Russell Condition n WMD (95% CI), kg P value
To contact an individual listed above, go to Weight stability 7 0.08 (−0.59, 0.75) .810
www.scandpg.org/executive-committee/ Weight loss without exercise 12 0.25 (−0.094, 0.60) .153
Weight loss with exercise 2 0.65 (0.16, 1.14) .009
Adults >50 y 5 0.91 (0.24, 1.60) .008
RDA = recommended dietary allowance
WMD = weighted mean difference
14
Values are from Hudson et al
2|SCAN’S PULSESpring 2021, Vol. 41, No. 2
FromThe Editor
Let Bygones Be Bye, Gone!
by Mark Kern, PhD, RD, CSSD, Editor-in-Chief
On the day that I write my last “From the Editor” letter for SCAN’s PULSE, I think of a quote from Henry Aaron, whose death was re-
ported just today. Hank Aaron, as he was commonly known, is credited as saying, “In playing ball, and in life, a person occasionally
gets the opportunity to do something great. When that time comes, only two things matter: being prepared to seize the moment
and having the courage to take your best swing.”
Well, as Editor-in-Chief of PULSE since late 2003, I have truly done my best to take my best swing, and I hope that at least occasion-
ally my best has been good enough. I started with PULSEwhen SCAN was trying to recover from a difficult time. The great Ellen
Coleman, who had stepped in as SCAN Chair along with other great leaders who helped take the reins of SCAN, offered me the po-
sition of Editor-in-Chief and told me she felt I was the right person to help turn PULSE around. Luckily, I have had our long-time and
incredibly talented Managing Editor, Annette Lenzi Martin, to show me the way.
Over that past many years, she and I have served PULSE as a faithful team, striving to ensure that every issue reached our readers
on schedule and that each was superbly edited for style, grammar, punctuation, and content. Since my early days with PULSE,
I have been enamored by Annette’s ability to edit article after article into pieces that were seemingly written by every author with
the same ease that Hammerin’ Hank displayed when homer after homer he smashed the Bambino’s home run record. Annette and
I haven’t done it all on our own, though. We had the example set by former Editor-in-Chief Michele Macedonio to help guide us
along our way, as well as the efforts of so many fellow editorial staff members, including our current exemplary editors.
I hope that our readers will find the articles and information in these final pages of PULSE to be worthy of the greatness of our es-
teemed publication, and that my many years of dedication to PULSEsuggest I was both prepared for the job at hand and ade-
quately courageous to complete it with unwavering enthusiasm.
— Mark
P.S. And, please, as I always say, be sure to read all of the other pages of PULSE, because as usual, I think we’ve knocked it out of the
ballpark!
gen balance and lean mass changes, it is tent catabolic stimulus that typically re- one modifiable means to decrease the
not possible to make a direct comparison sults in the reduction of skeletal muscle reduction of the body protein pool dur-
between achieving zero nitrogen bal- mass.15 Skeletal muscle serves as a func- ing moderate energy restriction by pro-
ance and the subsequent lean mass tional reservoir of amino acids to support viding the necessary precursor amino
change. However, the results suggest that peripheral and central tissue protein acids to stimulate protein synthesis. A
during periods most closely aligned with turnover and gluconeogenesis in a fasted few meta-analyses have demonstrated
the metabolic conditions stipulated in stated; skeletal muscle is also a major site that consuming a higher protein diet
-1 -1
the dietary reference intakes (DRI), the of glucose disposal and lipid oxidation. (range: 1.00-2.22 g·kg ·d ) promotes the
RDA for protein is sufficient to support Among observational studies, both attenuation of lean mass lost during en-
skeletal muscle in adults over the dura- higher muscle mass and higher strength ergy restriction;7, 8, 13 however, these
tion of several months. are related with more positive health meta-analyses have included studies
outcomes that promote a longer life and with control groups consuming less than
Weight Loss health span.16-18 As such, knowing the RDA. This could conceivably skew the
whether the current protein RDA is ade- effect size to indicate that consuming a
While the DRIs for protein are intended quate to attenuate the rapid losses in higher protein diet is beneficial when it
for healthy normal-weight adults in en- skeletal muscle during weight loss is cru- may be that consuming a lower protein
ergy balance, the growing participation cial information for registered dietitian diet (less than the RDA) results in lean
of adults in weight loss programs due to nutritionists working with clients seeking mass loss. To specifically address the ade-
excess body weight highlights purpose- weight loss. quacy of the protein RDA, a recent meta-
14
ful energy restriction as an important analysis included studies in which the
consideration. Energy restriction is a po- A higher intake of dietary protein may be control groups were prescribed the RDA
SCAN’S PULSESpring 2021, Vol. 41, No. 2 |3
-1 -1
(0.80 ± 0.05 g·kg ·d ). This meta-analysis gests that higher dietary protein intakes Conclusions
showed that a higher protein diet (~1.3 are needed to overcome this anabolic re-
-1 -1
g·kg ·d ) did not confer a protective ef- sistance to experience similar effects on In conclusion, regardless of age, the cur-
fect on lean body mass without a form of muscle mass. As such, it follows that rent protein RDA may be sufficient to
exercise present (0.25 kg [−0.094, 0.60]) higher total protein intakes may be support skeletal muscle mass during pe-
(Table 1).14These results suggest that needed to help slow the progressive loss riods of weight stability. However, in the
consuming ~60% more protein than the of skeletal muscle with advancing age.25 presence of weight loss, older, rather than
RDA does no better than the RDA to in- younger, adults may benefit from a
fluence skeletal muscle mass reductions The current DRIs do not delineate a sepa- -1 -1
higher protein intake up to 1.3 g·kg ·d .
with weight loss among healthy adults. rate requirement for older adults as too Resistance training is a potent anabolic
few studies have been available to render stimulus that will lead to gains in skeletal
Exercise a conclusive judgement. Results from -1 -1
muscle mass with intakes ≥0.8 g·kg ·d .
several prospective reviews suggest that Consuming a higher protein weight loss
Under normal conditions, gains in pro- older adults may need dietary protein in- diet while engaging in resistance training
tein mass that occur in a fed state takes that are higher than the RDA.26-29 will support skeletal muscle mass preser-
through stimulating protein synthesis These reviews mainly rely on results from -1 -1
vation. Intakes up to 1.6 g·kg ·d may be
and suppressing breakdown are suffi- acute stable isotope amino acid studies the upper optimal limit to support lean
cient only to replete body protein losses to make inferences about long-term mass gains that occur with resistance
that occur during a fasted state. With pro- changes in muscle mass. One longer- training but are not necessary to experi-
longed adherence to a resistance train- term study showed that in older adults ence lean mass gains.
ing program, protein deposition occurs. (>55 y) the RDA was adequate to achieve
Protein gain comes from achieving a net nitrogen balance; however, they experi- ____________________________
positive protein balance where synthesis enced an accommodating reduction in Joshua L. Hudson, PhD is a postdoctoral fel-
exceeds breakdown. Muscle protein syn- the thigh muscle area with weight stabil- low at the University of Arkansas for Med-
thesis rates have a saturable-dose re- ity.30 A “natural” loss in muscle size when ical Sciences and the Arkansas Children’s
sponse relation with dietary protein adequate energy is provided would indi- Nutrition Center in Little Rock, AR. Wayne
quantity.19 Specifically, the consumption cate that the RDA is insufficient. However, W. Campbell, PhD is a professor in the De-
of approximately 10 g of essential amino a 6-month study involving 92 older partment of Nutrition Science at Purdue
20 21
acids and approximately 3 g of leucine adults (>65 y) showed that consuming University in West Lafayette, IN.
-1 -1
maximizes this response. 1.3 g·kg ·d did not differentially influ-
ence changes in lean mass compared References
Indeed, several meta-analyses have with the RDA during periods devoid of 1. (US) Institute of Medicine. Dietary Ref-
shown that protein supplementation can stressors (i.e., weight stability).31These erence Intakes for Energy, Carbohydrate,
increase lean mass gain concurrent with data would seem to indicate that even Fiber, Fat, Fatty Acids, Cholesterol, Protein
6, 10
resistance training. In combination with high protein intakes, lean mass is and Amino Acids. National Academies
with energy restriction, consuming a not influenced by protein quantity when Press; 2005.
higher protein diet while engaging in a at least the RDA is consumed. Rather, in-
resistance training program also benefits creases in muscle mass (0.14 kg [-0.05, 2. Waterlow JC. The mysteries of nitrogen
lean mass retention (0.65 kg [0.16, 1.14]) 0.32]) or muscle strength (0.13 [kg -0.06 balance. Nutr Res Rev. Jun 1999;12:25-54.
(Table 1).14 Although the current protein to 0.32]) may best be achieved by engag- doi:10.1079/095442299108728857.
RDA is sufficient to support resistance- ing in a resistance training program with
training-induced lean body mass growth, adequate protein intakes (≥RDA).32When 3. Wolfe RR, Miller SL. The recommended
higher protein intakes up to approxi- older adults are exposed to a combina- dietary allowance of protein: a misunder-
-1 -1
mately 1.6 g·kg ·d may promote greater tion of anabolic or catabolic stimuli, con- stood concept. JAMA. Jun 25
10 -1 -1
lean mass growth. This suggests lean suming 1.1-1.5 g·kg ·d leads to greater 2008;299:2891-3. doi:10.1001/
body mass would increase with exercise lean mass gains (0.91 kg [0.24, 1.60]) jama.299.24.2891.
while concurrently consuming the pro- compared with the RDA (Table 1).14
tein RDA, but higher intakes (up to 1.6 4. Fukagawa NK. Protein requirements:
-1 -1
g·kg ·d ) may be “optimal.” Results from another meta-analyses also methodologic controversy amid a call for
show that consuming higher amounts of change. Am J Clin Nutr. Apr 2014;99:761-
Aging protein promoted greater lean body 2. doi:10.3945/ajcn.114.084772.
mass retention with weight loss (0.83 kg
Older adults typically experience a loss of [0.47, 1.19]).7These results suggest that 5. Nair KS, Halliday D, Griggs RC. Leucine
skeletal muscle at a rate of 1% to 2% per the RDA is adequate for healthy older incorporation into mixed skeletal muscle
year.22, 23 This may be caused by an in- adults who are not exposed to acute or protein in humans. Am J Physiol. Feb
creased anabolic resistance to dietary chronic illness that can stress protein 1988;254(2 Pt 1):E208-13.
protein intake. Compared with younger homeostasis, but with weight loss (with doi:10.1152/ajpendo.1988.254.2.E208.
adults, older adults experience a reduced or without exercise), higher protein in-
-1 -1
protein synthetic response to a similar takes (~1.3 g·kg ·d ) are associated with 6. Cermak NM, Res PT, de Groot LC, Saris
quantity of dietary protein.24This sug- greater lean mass. WH, van Loon LJ. Protein supplementa-
4|SCAN’S PULSESpring 2021, Vol. 41, No. 2
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