Beyond the zone: Protein needs of active individuals

Abstract

There has been debate among athletes and nutritionists regarding dietary protein needs for centuries. Although contrary to traditional belief, recent scientific information collected on physically active individuals tends to indicate that regular exercise increases daily protein requirements; however, the precise details remain to be worked out. Based on laboratory measures, daily protein requirements are increased by perhaps as much as 100% vs. recommendations for sedentary individuals (1.6-1.8 vs. 0.8 g/kg). Yet even these intakes are much less than those reported by most athletes. This may mean that actual requirements are below what is needed to optimize athletic performance, and so the debate continues. Numerous interacting factors including energy intake, carbohydrate availability, exercise intensity, duration and type, dietary protein quality, training history, gender, age, timing of nutrient intake and the like make this topic extremely complex. Many questions remain to be resolved. At the present time, substantial data indicate that the current recommended protein intake should be adjusted upward for those who are physically active, especially in populations whose needs are elevated for other reasons, e.g., growing individuals, dieters, vegetarians, individuals with muscle disease-induced weakness and the elderly. For these latter groups, specific supplementation may be appropriate, but for most North Americans who consume a varied diet, including complete protein foods (meat, eggs, fish and dairy products), and sufficient energy the increased protein needs induced by a regular exercise program can be met in one's diet.

Full text

Beyond the Zone: Protein Needs of Active Individuals
Peter W.R. Lemon, PhD
Exercise Nutrition Research Laboratory, The University of Western Ontario, London, Ontario, CANADA
Key words: amino acids, energy, physically active, exercise performance, athletes
There has been debate among athletes and nutritionists regarding dietary protein needs for centuries.
Although contrary to traditional belief, recent scientific information collected on physically active individuals
tends to indicate that regular exercise increases daily protein requirements; however, the precise details remain
to be worked out. Based on laboratory measures, daily protein requirements are increased by perhaps as much
as 100% vs. recommendations for sedentary individuals (1.6–1.8 vs. 0.8 g/kg). Yet even these intakes are much
less than those reported by most athletes. This may mean that actual requirements are below what is needed to
optimize athletic performance, and so the debate continues. Numerous interacting factors including energy
intake, carbohydrate availability, exercise intensity, duration and type, dietary protein quality, training history,
gender, age, timing of nutrient intake and the like make this topic extremely complex. Many questions remain
to be resolved. At the present time, substantial data indicate that the current recommended protein intake should
be adjusted upward for those who are physically active, especially in populations whose needs are elevated for
other reasons, e.g., growing individuals, dieters, vegetarians, individuals with muscle disease-induced weakness
and the elderly. For these latter groups, specific supplementation may be appropriate, but for most North
Americans who consume a varied diet, including complete protein foods (meat, eggs, fish and dairy products),
and sufficient energy the increased protein needs induced by a regular exercise program can be met in one’s diet.
Key teaching points:
• Dietary protein needs for physically active individuals have been controversial for many years.
• Generally, athletes have felt their needs are substantially greater than the recommendation from scientists - both opinions could be
correct as the latter is based on data from essentially sedentary subjects.
• Recent scientific study suggests a variety of factors need to be considered when determining protein requirements, including but
probably not limited to total energy intake, carbohydrate availability, exercise intensity, exercise duration, exercise type, dietary
protein quality, training history, gender, age and timing of nutrient intake.
• These studies indicate that for physically active individuals daily protein intake needs could be as high as 1.6–1.8 g/kg (about twice
the current recommendation).
• Despite these increased protein needs, assuming energy intake is sufficient to match the additional expenditures of training and
competition (which can be excessive), special protein supplementation is unnecessary for most who consume a varied diet
containing complete protein foods (meat, fish, eggs and dairy products).
• Those at greatest risk of consuming insufficient protein are those whose lifestyle combines other factors known to increase protein
needs with a regular exercise program, e.g., those with insufficient energy intake (dieters), growing individuals, vegetarians, the
elderly, those with muscle diseases and so on.
INTRODUCTION
In recent years, the multiple and varied health benefits
resulting from regular physical activity have become well doc-
umented; as a result, recommendations for increasing one’s
exercise level are becoming commonplace [1,2]. Although ath-
letes, especially those heavily involved with strength training,
have long believed that their protein intakes must be much
greater than for those who are sedentary, this opinion is derived
via nonscientific means. In contrast, the current recommended
dietary allowance (RDA) for protein does not recognize any
increased protein need for a physically active lifestyle [3].
However, even this scientific recommendation could be incor-
rect, as it is based on data collected from physically inactive or,
at best, minimally active individuals.
Throughout most of the 20
th
century, it has been assumed
Presented, in part, at a meeting sponsored by the American Egg Board and Egg Nutrition Center held at Amelia Island, FL on February 25–27, 2000.
An honorarium was provided for support of this manuscript by the Egg Nutrition Center.
Address reprint requests to: Dr. Peter W.R. Lemon, 3M Centre, The University of Western Ontario, London, Ontario N6A 3K7, CANADA. E-mail: plemon@julian.uwo.ca
Journal of the American College of Nutrition, Vol. 19, No. 5, 513S–521S (2000)
Published by the American College of Nutrition
513S

that physical exercise was an insufficient stimulus to alter
protein needs significantly, even though this question had not
been examined systematically in the scientific literature. In
light of the new physical activity recommendations, it is par-
ticularly important to know if regular exercise increases dietary
protein needs because, if so, following these guidelines could
lead to significant health problems related to sub-clinical/clin-
ical protein deficiency.
Perhaps also contributing to the debate among scientists and
athletes regarding dietary protein need is the fact that the
scientific studies have concentrated almost exclusively on lab-
oratory measures (primarily nitrogen balance), yet these may
not relate directly to exercise performance, which is, of course,
the main focus of the athletes. Further, although not always
appreciated, it is possible that, even if a measure like nitrogen
balance does not indicate an increased protein requirement,
exercise performance could still be enhanced by a greater
protein intake, i.e., the additional protein might alter a meta-
bolic process enhancing energy utilization for endurance per-
formance or could stimulate anabolism resulting in greater
muscle mass and/or strength gains. Hence the current recom-
mended protein intake could be sub-optimal for those who
regularly exercise. Fortunately, there is substantial recent sci-
entific information collected on physically active subjects
(completed after the current US recommendations were pub-
lished [3]), and much of this suggests that regular physical
activity can increase protein needs. These studies form the main
focus of this review. Finally, this area of research has become
far more popular, and, as more information becomes available,
the importance of related/influencing factors, including type of
protein or amino acids consumed, whether taken as a bolus or
in multiple intakes, when consumed throughout the day or
relative to the exercise sessions, age/gender/other foodstuff
interactions, as well as a variety of other factors, are beginning
to come into focus.
FACTORS WHICH APPEAR TO
AFFECT DIETARY PROTEIN NEED
Energy (Food) Intake
It has been known for about half a century that inadequate
energy intake leads to increased dietary protein needs [4],
presumably because some of the protein normally used to
synthesize both functional (enzymatic) and structural (tissue)
protein is utilized for energy under these conditions. Appar-
ently, this effect on protein need is similar when the energy
deficit is caused by increased energy expenditure (exercise)
[5,6]. In fact, this effect could be even more dramatic in those
who are physically active, as protein needs are likely already
increased in order to maintain a greater protein synthetic rate
due to the presence of greater absolute tissue (strength athletes)
or enzyme (endurance athletes) levels. In addition, there ap-
pears to be a gender difference in one’s ability to increase food
intake adequately with chronic high intensity exercise. Perhaps
for reasons related to maintenance of reproductive function in
times of energy deficit, females are better able to preserve
functional tissue than males whenever energy intake is low
[7–11]. Although this is of obvious benefit in a starvation
situation, for physically active females it often results in under-
eating relative to energy expenditure [12–16, Fig. 1). As a
result, females are able to maintain body mass at energy intakes
below the point where their male counterparts lose a significant
percentage of their mass. This may occur via some kind of
down-regulation of metabolism in females. Although not well
studied, this phenomenon could lead to a variety of nutrient
deficiencies because, as overall energy intake is reduced, so is
intake of most of the indispensable nutrients [15]. The details of
how this might alter protein need in men vs. women when
energy intake is insufficient is an area that requires much more
attention.
Carbohydrate Content
Carbohydrate availability to exercising muscle is critical for
intense muscle contraction, as it is a more efficient fuel (pro-
duces more adenosine triphosphate per unit of oxygen) than
both fat and protein. In combination with the fact that the total
carbohydrate stores in the body can be depleted in a single
exercise bout, this makes carbohydrate the single most impor-
tant exercise fuel. As a result, carbohydrate has been studied to
a much greater extent than either protein or fat. However,
inadequate carbohydrate for muscle contraction is also critical
because its availability is inversely related to the rate of exer-
cise protein catabolism (Fig. 2 [17]). Therefore, daily carbohy-
drate intake is of great significance for physically active indi-
viduals. Moreover, physically active individuals need to be
much less concerned about excess dietary carbohydrate intake
resulting in surplus body fat storage (and associated adverse
Fig. 1. Gender effects on energy (food) intake in physically active
individuals (SW ⫽swimmers, XSK ⫽cross-country skiers, RN ⫽
distance runners, WL ⫽weight lifters, BB ⫽bodybuilders, WR ⫽
wrestlers, BKB ⫽basketball players, GY ⫽gymnasts, BD ⫽ballet
dancers). While men typically increase their energy intake appropri-
ately for the increased expenditure of their activity (with the exception
of bodybuilders and wrestlers), women routinely fail to do so. (Adapted
from [12–16].)
Protein Needs and Exercise
514S VOL. 19, NO. 5

health effects) compared to their sedentary counterparts be-
cause this substrate is used to replenish carbohydrates stores
depleted by exercise training/competition sessions. In fact,
rather than over-consuming carbohydrate, athletes typically
have great difficulty replenishing carbohydrate stores following
exercise.
Exercise Intensity, Duration and Type
Increasing exercise intensity and duration, at least with
aerobic (endurance) exercise, causes increased use of protein,
presumably as an auxiliary fuel [18–21]. Based primarily on
nitrogen balance experiments, this results in an increased daily
protein need of about 50% to 75% (1.2–1.4 vs. 0.8 g/kg) when
compared to inactive individuals (Fig. 3 [22]). Although heavy
resistance (strength) exercise appears to increase protein need
by about 100% (1.6–1.8 vs. 0.8 g/kg) based on nitrogen balance
experiments (Fig. 4 [23]), isotope tracer studies have revealed
that the underlying mechanism is not increased fuel use [24].
Rather, it is the result of changes in muscle protein synthetic
rate (Fig. 5 [25]) and the need to maintain a greater overall
muscle mass [26]. If so, this raises an interesting question about possible interacting effects of other compounds and whether
some might be able to potentiate the already powerful anabolic
stimulus of strength exercise.
Recently, daily supplementation of creatine (⬃285 mg/kg),
a component of meat and fish, for as brief a time interval of
three to five days has been shown to enhance intense exercise
performance, especially when the exercise is repeated with
brief recovery intervals [27]. The underlying mechanism of
action is thought to involve additional phosphocreatine storage
in muscle, increased regeneration of phosphocreatine during
any brief recovery intervals and/or by buffering some of the
hydrogen ions formed during intense anaerobic exercise (Fig.
6). In our laboratory, we have seen this effect in both recre-
ational and elite athletes and have even observed a residual
performance effect lasting for at least four weeks following
cessation of supplementation (Fig. 7 [28]). Moreover, we have
recently measured (Table 1) greater gains in both muscle mass
and strength in subjects training with creatine and protein than
with protein alone [29, 30]. Although strength athletes can
Fig. 2. Nitrogen excretion increases with prolonged, moderately intense
exercise and especially so when carbohydrate stores are low. (Adapted
from [17].)
Fig. 3. Comparison of nitrogen balance (protein requirements) in
distance runners vs. sedentary subjects. (Adapted from [22].)
Fig. 4. Comparison of nitrogen balance (protein requirements) in
individuals who are strength training with differing protein intakes.
(Adapted from [23].)
Fig. 5. Effect of a strength training session on muscle protein synthesis.
(Adapted from [25].)
Protein Needs and Exercise
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 515S

increase muscle growth with supplemental protein, this effect
seems to attain a plateau at protein intakes (1.4 g/kg) far below
intakes typical of experienced bodybuilders (Fig. 8 [26]). Per-
haps these preliminary data indicate that the ceiling effect of
supplemental protein observed in strength athletes in the labo-
ratory studies (around 1.4 g protein/day) can be further raised
if combined with creatine. If so, this could explain, at least in
part, the opinion of strength athletes about protein needs be-
cause, even before the relatively recent popularity of creatine
supplementation, strength athletes have consumed routinely
huge amounts of meat and fish. Obviously, it is not possible to
consume sufficient meat/day to equal the creatine intake of
most studies demonstrating ergogenic effects (it would require
about 4–5 kg). However, it is interesting to note that much
more modest creatine supplementation (3 g/day) over a longer
time period (4 wk) can result in similar muscle creatine stores
[31]. Perhaps the intake of creatine (and/or some other com-
pound in meat and fish) in combination with the associated
large amino acid intake can explain why strength athletes
experience gains in mass and strength with protein intakes far
exceeding where the laboratory studies show no further gains.
This hypothesis needs to be examined.
Protein Quality
It is well known that humans can synthesize only about 50%
of the necessary amino acids that make up the proteins in our
bodies. Therefore, if the remaining amino acids (called indis-
pensable or essential) are not consumed in sufficient quantities,
protein production is affected adversely. The quality of protein
in a food is determined by its indispensable amino acid content
(Table 2 [32]). Some foods contain all of these indispensable
amino acids and in amounts sufficient to maintain protein
synthesis, while others are lacking in at least one amino acid.
The former are called complete protein foods and include such
foods as dairy products, eggs, meat and fish, while the latter
include grains, vegetables and fruits. Although it is also possi-
ble to obtain sufficient indispensable amino acids from a diet
that excludes complete protein foods entirely by combining
grains, vegetables and fruits, this requires some knowledge of
which foods to combine. As a result, vegetarians, especially
those that exclude eggs and dairy products, when they adopt a
physically active lifestyle constitute a group that is likely at
greater risk for insufficient dietary protein intake. Moreover, it
has been shown, at least in 59 to 69 year-old men, that strength
training produced greater muscle mass gains with a meat-
containing diet in comparison to a lactovegetarian diet [33].
These data suggest that type of protein may play an important
role in muscle growth with strength training. Whey protein,
especially whey protein isolates or hydrolyzed whey peptides,
is widely promoted to strength athletes as being perhaps the
best protein based on its high bioavailability and its content of
several critical amino acids, i.e., glutamine, leucine, isoleucine
and valine. We attempted to assess whether a whey protein
supplement could promote greater gains in muscle size and
strength with weight training in young men vs. casein, soy or
maltodextrin [34]. In this study all groups received a daily 0.7
g/kg supplement on top of their normal daily protein intake
which was 1.4–1.6 g/kg and, although all groups gained sig-
nificantly in both strength and size, there was no difference
among the groups. The obvious conclusion is that protein type
does not affect strength/size gains with strength exercise but,
because the response of the maltodextrin group was of the same
magnitude, it could be that the pre-supplementation protein
intake was already sufficient to maximize muscle growth. Ad-
ditional study is needed to clarify these possibilities. Whether
combining dietary proteins can further stimulate muscle growth
is another possibility which should be assessed because there is
evidence that, due to differing physiochemical properties, whey
protein amino acids enter the blood stream following ingestion
faster than casein (major milk protein), which produces a
significantly lower but more prolonged increase in blood amino
acids [35].
Training History
With regular endurance exercise (training) there appears to
be an increase in amino acid oxidation [36–38], likely due to
Fig. 6. Schematic representation of how creatine could enhance aden-
osine triphosphate availability and, consequently, intense exercise per-
formance.
Fig. 7. Effects of brief (5 day, 20 g/day) creatine supplemetation on
intense exercise performance (isokinetic knee extension [Nm] at 180°/
sec) over the subsequent 4 weeks. (Adapted from [28].)
Protein Needs and Exercise
516S VOL. 19, NO. 5

changes in branched-chain oxoacid dehydrogenase activity
[38]; however, more study is required, as at least one study
doesn’t support these data [39] and there is no apparent expla-
nation for these contradictory observations. With strength train-
ing there is also some confusion. Some initial work indicated
that protein needs to support the increased muscle growth at the
initiation of a bodybuilding program might exceed those nec-
essary to maintain the greater muscle mass later in training
[22], while other studies suggest that the need for protein
remains at similar levels for experienced strength athletes
[23,26]. Recently, at least with eccentric exercise, it has been
shown that, although muscle protein synthesis can be stimu-
lated with acute strength exercise in both resistance-trained and
untrained subjects, protein breakdown was greater in the latter
group [40]. These data provide mechanistic support for the
earlier observation that a single eccentric bout reduces subse-
quent muscle damage and pain [41] and may indicate that
initial increased protein needs with strength training are re-
duced with training experience. Before specific needs of expe-
rienced vs. novice strength athletes can be determined, more
work is necessary to ascertain exactly how these data all fit
together.
Gender
Most of the study of protein needs in physically active
individuals has been completed utilizing male subjects; how-
ever, there are data suggesting that protein utilization in
women, at least with endurance exercise, is significantly less
than in men [42,43]. Also, there are in vitro [44] and in vivo
[45] results indicating protein utilization with exercise is
greater in male than female rodents. The mechanism of action
could involve gender-specific hormonal responses that favor fat
metabolism in women (resulting in a reduced reliance on both
carbohydrate and protein [46]) or that protect the muscle mem-
brane from exercise-induced damage [47,48]. The effects of
strength training on protein requirements in female subjects has
not yet been studied systematically. Consequently, it remains to
be determined whether gender differences exist relative to the
quantity of dietary protein required to maximize muscle
growth.
Age
Sarcopenia is a term used to describe the loss of skeletal
muscle mass with advancing age. Functionally, as well as from
a health care point of view, this is of considerable significance
because it is associated with weakness and decreased indepen-
dence. This will be especially true over the next 20 to 30 years
given the large numbers of the baby boomer generation rapidly
approaching the point where sarcopenia will begin to affect
them. Although part of this muscle loss is likely the result of
reduced activity, physiological/biochemical processes are also
involved, as indicated by the 30% reduction in myofibrillar
protein synthesis in individuals over 60 years of age (Fig. 9
Table 1. Strength (Number of Repetitions at 80% of the Maximum Weight That Could Be Lifted One Time for the Double Leg
Press [1-RM]) and Arm Muscle Volume (10, 2 mm Contiguous Magnetic Resonance Slices) Changes with Seven Weeks of
Strength Training Combined with a Daily Supplement of Creatine⫹Protein vs. Protein or Creatine Alone [29,30].
Arm Volume Leg Press
Baseline Post Training Baseline Post Training
(mL) (# rep at 80% 1-RM)
Creatine ⫹Protein 103.1 ⫾5.9 116.7 ⫾6.8
ab
10.0 ⫾1.8 40.0 ⫾3.9
ab
Protein 86.8 ⫾4.9 94.4 ⫾4.2
a
7.7 ⫾0.7 23.9 ⫾1.8
a
Creatine 94.2 ⫾4.1 109.9 ⫾3.0
ab
11.9 ⫾1.5 29.8 ⫾3.6
ab
a
p⬍0.05 vs. baseline
b
p⬍0.05 vs. protein alone
Fig. 8. Effect of increasing protein intake on protein synthesis in
strength athletes vs. controls. (Adapted from [26].)
Table 2. Protein Digestibility-Corrected Amino Acid
Score [32].
Protein Source Score
Egg white 1.00
Casein (milk) 1.00
Isolated soy protein 1.00
Beef 0.92
Kidney beans 0.68
Rolled oats 0.57
Lentils 0.52
Whole wheat 0.40
Protein Needs and Exercise
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 517S

[49]). Further, muscle performance/function improves with
strength exercise even into the tenth decade of life [50], and this
is not due to improved neurological function alone, as three
months of regular strength exercise can increase mixed muscle
protein synthesis even in the frail elderly (76 to 92 year-old
men and women) [51]. Typically, nutrient intake is less than
ideal in the elderly and, although short term (10 day) energy
and protein supplementation can enhance protein synthesis and
fat-free mass in 60 to 90 year-old men and women [52],
whether nutritional supplementation might enhance further
muscle growth with strength exercise in the elderly is an
interesting possibility. One study observed that a 360 kcal (60%
carbohydrate, 23% fat, 17% protein) supplement in combina-
tion with a 10-week strength program increased both muscle
strength and size more that the same training without supple-
mentation in 72 to 98 year-old men and women [53]. In
contrast, acute (one-day) feeding of protein at 0.6, 1.2, or 2.4
g/kg did not affect myofibrillar protein synthesis following a
very brief (three-session) knee extension program [54]. Al-
though this could implicate energy rather than protein as the
major anabolic stimulus, it is likely the answer to these con-
tradictory data is far more complicated. For example, the acute
vs. chronic exercise stimulus or the length of the time on the
treatment diets could both be important. Finally, at least in
older women (60 to 73 years) over a 14-day time period, a pulse
intake of protein (7% at 0800, 79% at 1200, 14% at 2000) vs.
spread (25% at each of 0800, 1200, 1600, 2000) produced a
greater gain in fat free mass [55]. Consequently, mass of
protein consumed and/or timing of intake (see below) may also
be critical, although this latter study did not involve any exer-
cise and, therefore, may apply only to a sedentary individuals.
The other end of the age continuum is also of interest
because dietary protein needs are known to be greater due to
growth [3]. Although not systematically investigated, it is pos-
sible that regular physical activity could further increase pro-
tein requirements for this population [56–58]. For similar rea-
sons, women who actively exercise during pregnancy are
another high risk group where supplementary protein/energy
may be advantageous.
Timing of Macronutrient Intake
It is clear that carbohydrate intake immediately following
glycogen-depleting exercise can enhance subsequent muscle
glycogen resynthesis when compared to the same intake several
hours later [59]. Similarly, it could be possible to stimulate
muscle growth (by minimizing degradation and/or maximizing
synthesis) via carbohydrate or amino acid ingestion following a
strength exercise session [60,61]. This is likely due to insulin-
stimulated [62,63] changes in muscle amino acid uptake and
protein synthesis (Fig. 10 [62]). Further, it appears that the
nonessential (dispensable) amino acids are unnecessary (Fig.
11 [62]). We know that a strength training session affects both
muscle protein degradation and synthesis (Fig. 12), but the
precise magnitude of the responses and the time course is yet to
be determined [64,65]. As these responses become clear, it
might be possible to make very precise recommendations to
maximize the anabolic stimulus following strength training.
Clearly, this would benefit a variety of populations in addition
to athletes, i.e., those who have lost muscle function due to
disease, disuse and the like. The latter could be very critical
relative to both quality of life and even to health care costs as the
large numbers of baby boomers pass into the senior age groups.
SUMMARY
A variety of factors interact to increase dietary protein needs of
individuals who exercise regularly. Although future study will
need to determine precise recommendations, current research in-
dicates that as long as energy intake is adequate a daily protein
intake of 1.2–1.4 g/d for individuals participating in regular en-
durance exercise and 1.6–1.8 g/kg for their counterparts involved
in strength exercise (Fig. 13) should be sufficient. To ensure these
increased needs are met, care should be taken to consume a diet
containing adequate energy and a selection of high quality protein
foods, i.e., dairy products, eggs, meat, fish and soy products.
Select populations may be at increased risk of not consuming
sufficient protein due to increased requirements for a variety of
Fig. 9. Effect of age on muscle protein synthesis. (Adapted from
reference 49.)
Fig. 10. Effect of indispensable amino acid intake following strength
exercise on insulin release. (Adapted from [62].)
Protein Needs and Exercise
518S VOL. 19, NO. 5

other reasons, i.e., unbalanced diet (vegetarians), inadequate en-
ergy intake (dieters or athletes with high energy expenditure,
especially women), higher baseline requirements (those who are
growing or the elderly) and so on. More study is necessary before
all of this can be untangled.
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