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Abstract and Figures

Proper nutrition is an essential element of athletic performance, body composition goals, and general health. Although natural variability among persons makes it impossible to create a single diet that can be recommended to all; examining scientific principles makes it easier for athletes and other physically active persons to eat a diet that prepares them for successful training and/or athletic competition. A proper nutritional design incorporates these principles and is tailored to the individual. It is important for the sports nutritionist, coach, and athlete to understand the role that each of the macronutrients plays in an active lifestyle. In addition, keys to success include knowing how to determine how many calories to consume, the macronutrient breakdown of those calories, and proper timing to maximize the benefits needed for the individual’s body type and activity schedule. Key wordsSport-specific eating–Carbohydrate–Fat–Protein–Nutrient timing–Energy expenditure–URTI
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4
Macronutrient Intake
for Physical Activity
Thomas Buford
Abstract
Proper nutrition is an essential element of athletic performance, body
composition goals, and general health. Although natural variability among
persons makes it impossible to create a single diet that can be recommended to
all; examining scientific principles makes it easier for athletes and other phy-
sically active persons to eat a diet that prepares them for successful training
and/or athletic competition. A proper nutritional design incorporates these
principles and is tailored to the individual. It is important for the sports
nutritionist, coach, and athlete to understand the role that each of the macro-
nutrients plays in an active lifestyle. In addition, keys to success include
knowing how to determine how many calories to consume, the macronutrient
breakdown of those calories, and proper timing to maximize the benefits
needed for the individual’s body type and activity schedule.
Key words
Sport-specific eating
Carbohydrate
Fat
Protein
Nutrient timing
Energy expenditure
URTI
1. INTRODUCTION
Proper nutrition is an essential element of athletic performance,
body composition goals, and general health. Although the natural
variability among persons makes it impossible to create a single diet
that can be recommended to all; examining scientific principles
makes it easier for athletes and other physically active persons to
eat a diet that prepares them for successful training or athletic
competition. The purpose of this chapter is to discuss the three
major nutrients that make up the bulk of energy intake and how
From: Nutritional Supplements in Sports and Exercise
Edited by: M. Greenwood, D. Kalman, J. Antonio,
DOI: 10.1007/978-1-59745-231-1_4, Ó Humana Press Inc., Totowa, NJ
95
they fit into the diet of those with a physically active lifestyle.
Throughout the chapter the term athlete is used often, but it is
meant to refer to anyone with a physically active lifestyle.
Designing a nutr itio nal program for an athlete can be viewed
much like the process of e xercise prescription. The ‘nutritional
design’ should be individ ualiz ed, taking into ac count factors such
as age, size, sex, training regimen, and bioenergetic demands of
the activity or sport. Much like the concept of sport-specific
training, to maximiz e the bene fits of tra ini ng and/or ev ent per for -
mance one nee ds to implement a syste m o f ‘sport-specif ic eat ing. ’
To do this, it is necessary to understand the primary energy
systems used during a particular activit y. Prope r calorie nee ds,
macronutrient ratios, and nutrient timing issues can then be
addressed.
The aim of this chapter is to provide a framework that allows
athletes, coaches, and sports nutritionists to make successful food
and supplement choices. Hopefully, these choices will enable the
athlete to train at maximal capacity, compete at maximal ability,
and/or reach fitness goals while maintaining proper health.
However, this framework must not be confused with a recipe.
Each individual responds differently to a given diet, so an athlete
must take these recommendations and adjust if her/his body does
not respond as wished.
2. MACRONUTRIENTS
Macronutrients consist of the three nutrients that are required
in large quantities in the diet: carbohydrates, proteins, and fats.
These nutrients provide the energy required to maintain the body’s
functions as well as uphold cellular structure and homeostasis.
Whether in energy production or cellular structure, these nutrients
play a vital role in athletic performance as well as the overall health
of an individual.
2.1. Carbohydrates
Carbohydrates are naturally occurring compounds that are
composed of carbon, hydrogen, and oxygen. It was once thought
96 Buford
that carbohydrates adhered to a chemical structure of C
x
(H
2
O)
y
.
However, this structure does not encompass all carbohydrates, but
it does include other noncarbohydrate compounds such as acetic
acid. A newer definition defines carbohydrates as polyhydroxy
aldehydes or ketones and their derivatives.
There are three major classes of carbohydrates: monosacchar-
ides, oligosaccharides, and polysaccharides. Monosaccharides are
single sugar molecules and include glucose (also known as dextrose
in the diet), fructose, and galactose. Oligosaccharides are chains of
sugars that contain two to ten monosaccharides, the most common
being disaccharides such as lactose, maltose, and sucrose. Polysac-
charides are complex carbohydrates that contain possibly thou-
sands of monosaccharides. Starches and fibers are the primary
types of dietary polysaccharide. Glycogen is a polysaccharide
that is also the storage form of glucose in the body and is found
primarily in the liver and skeletal muscle.
Simple carbohydrates are primarily more calorie-dense, yet less
nutrient-dense, than complex carbohydrates. Monosaccharides are a
major problem in the sedentary population because of the low meta-
bolic cost and ease in which they can convert to fat when in calorie
excess. Polysaccharides are generally promoted because of their abil-
ity to be absorbed more slowly and provide greater nutrient value.
Starch is the storage form of carbohydrate in plants, and it can be
found in grains, nuts, legumes, and vegetables. It is a viable energy
source because it digests slowly and provides energy for longer peri-
ods than does simple carbohydrate. Fiber, on the other hand, is
indigestible and is useful in slowing the digestive rate of food,
removing toxins, and adding bulk to the feces. It is found in foods
such as vegetables, fruits, nuts, and legumes. The National Cancer
Institute recommends 20 to 30 g of fiber per day for proper health.
Two types of fiber exist: soluble and insoluble. Soluble fibers dissolve
in water and slow the rate at which food travels through the small
intestine, thereby maximizing nutrient uptake time. Soluble fibers can
be found in foods such as wheat, rye, rice, and bran. Insoluble fiber,
or cellulose, on the other hand does not dissolve in water and serves to
remove toxins from and add bulk to the fecal matter. Cellulose can be
found in oats, legumes, beans, and many fruits and vegetables.
It may sound as if simple carbohydrates are vastly inferior to
complex carbohydrates, but a mix of carbohydrate types is beneficial
Macronutrient Intake for Physical Activity 97
for supplying athletes with energy. In fact, isolated dextrose and
fructose can be useful in sports drinks or carbohydrate gels for athletes,
and complex carbohydrates may increase glucose levels greatly.
Although first developed for use with diabetics, the glycemic index
(GI) provides a useful tool for helping athletes with food choices
(Table 1). The GI value is a measure of how much and how long a
particular food raises blood glucose levels. The values are based on a
standard of 100, which is the value for glucose or white bread. Often,
people mistake the GI as a function of whether foods are simple or
complex. However, some complex carbohydrates (e.g., baked potatoes)
Table 1
Glycemic Index of Common Foods
a
Low-GI foods GI Medium GI
foods
GI High GI
foods
GI
Roasted and
salted peanuts
14 Boiled
potatoes
56 Mashed
potato
70
Low-fat yogurt
with
sweetener
14 Sultanas 56 White bread 70
Cherries 22 Pita bread 57 Watermelon 72
Grapefruit 25 Basmati rice 58 Swede 72
Pearl barley 25 Honey 58 Bagel 72
Red lentils 26 Digestive
biscuit
59 Bran flakes 74
Whole milk 27 Cheese and
tomato
pizza
60 Cheerios 74
Dried apricots 31 Ice cream 61 French fries 75
Butter beans 31 New potatoes 62 Coco Pops 77
Fettuccine pasta 32 Coca cola 63 Jelly beans 80
Skimmed milk 32 Apricots,
canned in
syrup
64 Rice cakes 82
Low-fat fruit
yogurt
33 Raisins 64 Rice
Krispies
82
Whole grain
spaghetti
37 Shortbread
biscuit
64 Cornflakes 84
98 Buford
Table 1
(continued)
Low-GI foods GI Medium GI
foods
GI High GI
foods
GI
Apples 38 Couscous 65 Jacket
potato
85
Pears 38 Rye bread 65 Puffed
wheat
89
Tomato soup,
canned
38 Pineapple,
fresh
66 Baguette 95
Apple juice,
unsweetened
40 Cantaloupe
melon
67 Parsnips,
boiled
97
Noodles 40 Croissant 67 White rice,
steamed
98
White spaghetti 41 Shredded
wheat
67
All Bran 42 Mars bar 68
Chick peas,
canned
42 Ryvita 69
Peaches 42 Crumpet,
toasted
69
Oranges 44 Wholemeal
bread
69
Macaroni 45
Green grapes 46
Orange juice 46
Peas 48
Baked beans in
tomato sauce
48
Carrots, boiled 49
Milk chocolate 49
Kiwi fruit 52
Crisps 54
Banana 55
Raw oat bran 55
Sweetcorn 55 .
GI, glycemic index.
a
Based on glucose (GI = 100) as a standard.
See Foster-Powell (1) for a more complete list.
Macronutrient Intake for Physical Activity 99
increase glucose levels similarly to glucose. These values can be
helpful for athletes to determine food choices when they want to
increase glucose/glycogen levels quickly.
2.2. Protein
Proteins are nitrogen-containing compounds composed of
dozens, hundreds, or thousands of amino acids. Amino acids are
joined by peptide bonds, and several amino acids joined together
become a polypeptide. Polypeptide chains then bond together and
form various proteins. Chemically, proteins can be divided into
groups: simple or conjugated. Simple proteins contain only amino
acids or their derivatives. More recognizable to the nutritionist
are conjugated proteins, which contain some nonprotein substance
such as sugar molecules (glycoproteins), lipids (lipoproteins), or
phosphate groups (phosphoproteins).
The human body is composed of 18% protein on average.
Proteins provide structure to bodily tissues such as skeletal muscle,
connective tissue, bone, and organs. In addition, nonstructural
proteins act as hormones, catalysts (enzymes), buffer systems, cel-
lular water balance regulators, lubricants, and immunoregulatory
cells. Noting these numerous functions, the value of proteins in
the body cannot be underestimated. In contrast to carbohydrates
and fat, the body has no physiological reserve of protein stores.
Therefore, if the body is not sufficiently supplied with protein, it
catabolizes tissue proteins and cellular function is lost.
For nutritional purposes, amino acids can be divided into two
general groups: essential and nonessential. Determining whether an
amino acid is essential or nonessential hinges on whether the body
synthesizes sufficient amounts to meet its own needs (nonessential)
or if the diet must provide them (essential). The essential and non-
essential amino acids are listed in Table 2. The most important of
the essential amino acids are the branched-chain amino acids
(BCAAs). The BCAAs are made up of leucine, isoleucine, and
valine. These amino acids are available for uptake directly by the
skeletal muscle without having to be metabolized by the liver. Many
new protein supplements are either supplementing whole protein
with the BCAAs or are simply marketed as the BCAAs themselves.
In addition, a helpful stratification of dietary proteins is to deter-
mine if the protein is complete or incomplete. Primarily in animal
100 Buford
products, proteins that contain the proper quantity and balance of
essential amino acids are known as complete proteins. Meat, fish,
eggs, milk, and cheese are all good sources of complete proteins.
Incomplete proteins, on the other hand, lack one or more essential
amino acids or are imbalanced in regard to essential amino acids. A
few animal products may be incomplete, but they are primarily
located in plant protein sources such as grains, beans, or vegetables.
It can often be a challenge for vegetarian athletes to obtain proper
amounts of all essential amino acids when forced to eat many plant
sources in combination. (Further discussion of the vegetarian diet
can be found in the sidebar at the end of the chapter.)
2.3. Fat
Lipids comprise a broad group of water-insoluble, energy-dense
compounds made up of carbon, hydrogen, and oxygen. Often the
terms fat and lipid are used interchangeably, although they are
indeed different. Lipids include fats and oils in the body as well as
fatty compounds such as sterols and phospholipids. Fats are speci-
fically esters formed when fatty acids react with glycerol. Many
other lipids exist and are significant in the diet. The lipids of greatest
importance in the body and the diet are triglycerides, fatty acids,
phospholipids, and cholesterol (2). For the purposes of this chap-
ter, the terms fat and fats are used to refer to dietary lipids.
Table 2
Essential and Nonessential Amino Acids
Essential Nonessential
Histidine
a
Alanine
Isoleucine Arginine
Leucine Asparagine
Lysine Aspartic acid
Methionine Cysteine
Phenylalanine Glutamic acid
Threonine Glutamine
Tryptophan Glycine
Valine Proline
a
Some adults may be able to synthesize histidine
on their own
Macronutrient Intake for Physical Activity 101
Weight gain is often attributed to fats because they contain
far more energy per gram than does carbohydrate or protein
(9 kcal/g vs. 4 kcal/g, respectively). Because of this tendency (weight
gain with overconsumption of fats) and their role in disease devel-
opment, fats are often viewed in a highly negative light. However,
fats serve many functions in the body: They provide energy for
tissues and organs, membrane makeup, nerve signal transmission,
and vitamin transport as well as cushioning and insulation for
internal organs. In addition, in endurance athletes they are a vital
fuel source for skeletal muscle.
The primary fats found in large quantities in foods are triglycer-
ides. Triglycerides are composed of three fatty acids and one
glycerol molecule. Fatty acids can be grouped by the amount of
hydrogen they contain, otherwise known as saturation. Saturated
fatty acid chains contain no double bonds; monounsaturated fatty
acids contain one double bond; and polyunsaturated fats have
multiple double bonds. Triglycerides typically contain a mix of the
three fatty acid types. The ratio of unsaturated to saturated fatty
acids is known as the P/S ratio. Animal fats usually have a low P/S
ratio, whereas most vegetable oils (except tropical plant oils) have
a high P/S ratio. The fatty acid makeup of the triglycerides is
important to its metabolism in the body. For example, saturated
fats may increase cholesterol in the body, whereas unsaturated fats
may have no effect or lower cholesterol.
Cholesterol is found in small amounts in food and is generated by
the body. High density lipoproteins (HDLs) are a type of cholesterol
composed of a high protein to fat ratio. HDL is typically known as
‘good’ cholesterol because of its protective nature against heart
disease, whereas low-density lipoproteins (LDLs) are negative risk
factors for heart disease. LDL is primarily fat with low amounts of
protein.
There are two types of fatty acid in the diet that require pay
special attention. First, essential fatty acids are not synthesized in
the body and therefore must be taken in through the diet. The
essential fatty acids are linoeic (omega-6) and linolineic (omega-3),
both 18-carbon fatty acids. Linoeic acid is found in oils of plant
origin, whereas marine oils are a good source of linolenic acid. The
other type of fatty acid that needs attention is the trans fatty acid.
‘Trans fats’ as they are commonly known, are often oils that are
102 Buford
solidified through a process known as dehydrogenation, although
some amounts are found naturally. Trans fats are in foods such as
margarine, shortening, and some dairy products. The reduction of
trans fats has become a point of public scrutiny in places such as fast
food and packaged foods because although they are unsaturated
fats they behave like saturated fats in the body. Trans fats appear to
promote myriad diseases, including heart disease, diabetes, and
obesity (3).
Generally, fruits and vegetables contain little fat. Animal pro-
ducts such as meat, milk, cheese, and eggs, as well as baked goods,
generally contain high amounts of saturated fats. Nuts and peanut/
canola oils can be good sources of monounsaturated fats. Polyun-
saturated fats, including the essential fatty acids, can be found in
fish, nuts, and corn, soy, and sunflower oils. Lastly, margarine,
shortening, cookies, pastries, and fried foods have high levels of
trans fats.
2.4. Metabolic Usage
Paramount to understanding ‘sport-specific’ eating and proper
food decisions is a basic knowledge of the metabolic usage of the
macronutrients in the body. This chapter provides only a cursory
overview of the bioenergetics of activity and exercise, yet these
principles are essential to a proper nutritional design. Gluconeo-
genesis, or energy production from protein sources, is a minor
source of energy production, but its major functions include struc-
tural and enzymatic functions. Therefore, the discussion here is
limited to energy production from carbohydrates and fats.
The primary energy systems used depend on the intensity and
duration of the exercise. Short, quick bursts (e.g., vertical jumping
or throwing events) are supplied by the ATP system. Sprints (quick
events up to 10 seconds) are supplied via the ATP þ phosphocreatine
(PCr) system. Anaerobic power endurance events (e.g., 200 or
400 meter dashes) are supplied by ATP, PCr, and anaerobic glyco-
lysis. Endurance events (> 800 meters) are supplied successively by
glycolysis, the tricarboxylic acid (TCA) cycle, the electron transport
chain (all carbohydrate metabolism), and eventually fat oxidation.
In terms of carbohydrate and fat oxidation, a simple rule is the
higher the intensity the more carbohydrate that is burned. In
addition, the longer the duration, the more fat is utilized. This
Macronutrient Intake for Physical Activity 103
means that even activity that begins at high or moderate levels
tapers off due to glycogen depletion, and fat becomes the primary
fuel after 20 to 30 minutes of continual exercise. These basic con-
cepts are essential to ‘nutrient load’ adequately for the activity or
event.
When comparing energy reserves, the human body has far more
fat than glycogen stores. Skeletal muscle glycogen stores number
around 400 g for an 80 kg individual, with an additional 100 g stored
in the liver. In comparison, that same 80 kg individual may have
more than 12,000 g of fat stored in adipose tissue. When factoring in
the fact that fat is more than twice as calorie dense as carbohydrate,
the energy stores are quite unbalanced. However, although each
fatty acid provides 147 ATP and each triglyceride provides 460
ATP, glucose metabolism (36 ATP/molecule) is more efficient
per unit of oxygen at providing energy. In addition, it takes roughly
20 minutes for free fatty acids to be liberated for use through
lipolyis. Per unit of time, therefore, glucose is more efficient and
thus the preferred fuel for high intensity exercise. These data help
detail the merits of both fats and carbohydrates as fuel sources. The
importance of these fuels should not be underestimated by the
athlete when considering intake or expenditure.
3. DETERMINING INTAKE NEEDS
Possibly the most important piece of the nutritional puzzle for
athletes is the understanding of how to determine the right amount
of calories and macronutrients to consume. After all, what good is
an understanding of what the nutrients are for athletes if they do not
know how much they need to take in?
The initial consideration when determining macronutrient needs
is to determine the goal of the nutritional design. Is the goal to
maintain, lose, or gain weight? Or is there a body composition
goal such as gaining muscle mass or maximizing strength while
maintaining a certain body weight? Second, one must consider the
bioenergetics of the event or training required to meet the goal. For
example, high intensity, high frequency resistance training requires
higher levels of protein intake than other forms of exercise. Finally,
physiological factors such size, age, and sex play a role in caloric
104 Buford
needs as well as the macronutrient distribution of those calories.
For example, older athletes may need higher protein intake to pre-
vent muscle loss and/or bone resorption, and highly active women at
risk for amenorrhea may need to increase caloric intake and fat
consumption.
3.1. Determining Caloric Needs
To determine macronutrient intake needs, one must begin by
determining the caloric needs of the individual. Total energy expen-
diture (TEE) is composed of four factors: resting metabolic rate
(RMR), exercise energy expenditure, thermogenesis, and activities
of daily living.
The RMR accounts for the greatest percentage of calorie expendi-
ture. RMR is positively correlated with the size and the amount of lean
body mass a person has. The percentage of TEE from the RMR
depends on the fitness and activity level of the individual, but it gen-
erally accounts for 60% to 70% of daily energy expenditure. As a
person becomes more active, the RMR begins to account for a slightly
lower percentage of energy expenditure. RMR values below 50% of
the TEE have even been reported in male endurance athletes (4).
The simplest and most accessible method for determining RMR
is to use the Harris and Benedict equations (5). These formulas
require the height (in centimeters), weight in kilograms, and age
(in years) to predict the daily RMR. The formulas are as follows.
Males: RMR (kcal/day) = 66.47 þ 13.75(weight) þ 5(height)
6.76(age)
Females: RMR (kcal/day) = 655.1 þ 9.56(weight) þ 1.85(height)
4.68(age)
Even though these equations do not take into account the fat
free mass, they have been reported to predict the RMR within
200 kcal/day in endurance athletes of both sexes (6). The most
accurate ways to measure RMR include chamber indirect calori-
metry and the use of metabolic carts equipped with RMR software.
These methods are quite pricey, however, and not practical for
most sports nutritionists, coaches, or athletes. Newer methods are
becoming increasingly available to provide more individualized data
Macronutrient Intake for Physical Activity 105
than the formulas in a less expensive, portable form. Although
several brand models exist (not discussed here), most of these por-
table RMR devices are fast and relatively accurate compared to the
gold standard methods.
Once the RMR has been established, the next step is to determine
the daily energy expenditure from physical activity. Exercise energy
expenditure and activities of daily living are often combined into a
physical activity. If this is done, it is important to remember to factor
in daily activities such as walking up/down stairs, yardwork, or even
shopping. These activities take small amounts of energy to complete
but energy nonetheless. The athlete’s training routine must also be
taken into account. Caloric expenditure tables provide estimates of
the energy requirements of many activities per minute (Table 3). To
find the energy expenditure from physical activity per day, simply
multiply the expenditure per minute by the number of minutes
participating in the activity per day.
The final component of TEE is thermogenesis, which is energy
expenditure not accounted for by RMR or activity. The most
important form of thermogenesis is the thermic effect of food.
The metabolic rate increases during the digestive processes, which
increases energy expenditure. Fats and simple sugars have the lowest
metabolic cost, whereas proteins and complex carbohydrates
take more energy to digest. The thermic effect of food generally
accounts for 5% to 10% of the TEE.
The TEE determines the number of calories the athlete needs
per day to stabilize his or her body weight. If, however, a change
in body weight is desired, as in the case of weight-dependent or
muscle building sports; the daily caloric intake must be adjusted
as such. One pound is equivalent to 3500 calories, therefore a
3500 calorie deficit/excess over a given period of time results in a
loss/gain of 1 pound. Safe weight loss/gain guidelines generally
recommend weight change of 1 to 2 pounds per week. Therefore,
to achieve weight loss of 1 pound per week, for example, the athlete
would need to consume 500 fewer kilocalories per day than the TEE.
3.2. Determining Macronutrient Intake
Once the daily caloric intake is determined, the question becomes
how to determine what foods to eat. Although each athlete has indivi-
dualized needs based on the sport’s requirements, a good starting point
106 Buford
Table 3
Metabolic Expenditure of Given Activities
Metabolic expenditure (kcal/min), by body weight (kg/lb)
45.0/ 48.0/ 50.0/ 52.0/ 55.0/ 57.0/ 59.0/ 61.0/ 64.0/ 66.0/ 68.0/ 70.0/ 73.0/ 75.0 77.0 80.0 82.0 84.0 86.0 89.0 91.0 93.0 95.0 98.0 100.0
Activity 100.0 105.0 110.0 115.0 120.0 125.0 130.0 135.0 140.0 145.0 150.0 155.0 160.0 165.0 170.0 175.0 180.0 185.0 190.0 195.0 200.0 205.0 210.0 215.0 220.0
Light work, cleaning 2.7 2.9 3.0 3.1 3.3 3.4 3.5 3.7 3.8 3.9 4.1 4.2 4.4 4.5 4.6 4.8 4.9 5.0 5.2 5.3 5.4 5.6 5.7 5.9 6.0
Basketball, vigorous 6.5 6.8 7.2 7.5 7.8 8.2 8.5 8.8 9.2 9.5 9.9 10.2 10.5 10.9 11.2 11.5 11.9 12.2 12.5 12.9 13.2 13.5 13.8 14.2 14.5
Bicycling
10 mph
4.2 4.4 4.6 4.8 5.1 5.3 5.5 5.7 5.9 6.1 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.9 8.1 8.3 8.5 8.7 8.9 9.1 9.4
15 mph 7.3 7.6 8.0 8.4 8.7 9.1 9.5 9.8 10.0 10.5 10.9 11.3 11.6 12.0 12.4 12.7 13.1 13.4 13.8 14.2 14.5 14.9 15.3 15.6 16.0
Golf, twosome (no
cart)
3.6 3.8 4.0 4.2 4.4 4.6 4.7 4.9 5.1 5.3 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.7 6.9 7.1 7.3 7.4 7.6 7.9 8.0
Running
5 mph
6.0 6.3 6.6 7.0 7.3 7.6 7.9 8.2 8.5 8.8 9.1 9.4 9.7 10.0 10.3 10.6 10.9 11.2 11.6 11.9 12.2 12.5 12.8 13.1 13.4
7 mph 8.5 8.9 9.3 9.8 10.2 10.6 11.0 11.5 11.9 12.3 12.8 13.2 13.6 14.1 14.5 14.9 15.4 15.8 16.2 16.6 17.1 17.5 17.9 18.4 18.8
9 mph 10.8 11.3 11.9 12.4 12.9 13.5 14.0 14.6 15.1 15.7 16.2 16.8 17.3 17.9 18.4 19.0 19.5 20.1 20.6 21.2 21.7 22.2 22.8 23.3 23.9
11 mph 13.3 14.0 14.6 15.3 16.0 16.7 17.3 18.0 18.7 19.4 20.0 20.7 21.4 22.1 22.7 23.4 24.1 24.8 25.4 26.1 26.8 27.5 28.1 28.8 29.5
Tennis, competitive 6.4 6.7 7.1 7.4 7.7 8.1 8.4 8.7 9.1 9.4 9.8 10.1 10.4 10.8 11.1 11.4 11.8 12.1 12.4 12.8 13.1 13.4 13.7 14.1 14.4
Walking
2 mph
2.1 2.2 2.3 2.4 2.5 2.6 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.9 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7
3 mph 2.7 2.9 3.0 3.1 3.3 3.4 3.5 3.7 3.8 3.9 4.1 4.2 4.4 4.5 4.6 4.8 4.9 5.0 5.2 5.3 5.4 5.6 5.7 5.9 6.0
4 mph 4.2 4.4 4.6 4.8 5.1 5.3 5.5 5.7 5.9 6.1 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.9 8.1 8.3 8.5 8.7 8.9 9.1 9.4
Weight training 5.2 5.4 5.7 6.0 6.2 6.5 6.8 7.0 7.3 7.6 7.8 8.1 8.3 8.6 8.9 9.1 9.4 9.7 9.9 10.2 10.5 10.7 11.0 11.2 11.5
Wrestling 8.5 8.9 9.3 9.8 10.2 10.6 11.0 11.5 11.9 12.3 12.8 13.2 13.6 14.1 14.5 14.9 15.4 15.8 16.2 16.6 17.1 17.5 17.9 18.4 18.8
Adapted from Nutrition for Sport and Exercise (pp 262–265). ed 2. Aspen, New York, 1998.
107
for prescribing macronutrient intake is to try to have a diet that is near
60% carbohydrates (with most of them being complex), 15% protein,
and 25% fat. These numbers can be slightly adjusted based on the
needs of the individual, as diets with various macronutrient mixtures
have been proven to be effective for training and performance (7–9).
For example, an athlete in a weight-dependent sport who is trying to
lose weight may want to reduce fat intake because of the calorie density
of the substrate. On the other hand, athletes participatin g in resistance
training may benefit from an increased percentage of protein com-
pared to the other two fuel sour ces. Vegetarian athlete s also require
greater protein requirements owing to a lack of high quality meat
proteins in the diet.
A second factor to consider is the daily recommendations for
carbohydrate and protein. Beginning with protein, the general
guideline for sedentary individuals is to intake 0.8 g/kg body
weight. Endurance athletes have been recommended to consume
up to 1.4 g of protein/kg/day (10). These athletes may require larger
amounts of protein owing to repetitive motion breakdown of con-
tractile proteins. In addition, BCAAs may be important for endur-
ance athletes in delaying fatigue in respect to the central fatigue
hypothesis. New research reported that dietary protein intake as
high as 1.8 g/kg stimulated protein synthesis following endurance
exercise, but further research is needed (11). For athletes participat-
ing in regular resistance training, larger amounts of protein are
needed to maintain an anabolic environment and increase muscle
mass. Protein at 1.7 to 1.8 g/kg is generally recommended for strength
training (12), although 2.0 g/kg may ensure adequate intake. There
is no evidence indicating the usefulness of > 2.0 g/kg, and it has been
reported that 2.4 g/kg provided no greater benefit in increasing
protein synthesis than a moderate protein diet (13). On the other
end of the spectrum, the athletes at greatest risk for deficient
protein intake are those in weight-restrictive sports (e.g., wrestling,
gymnastics) who are restricting calories.
Carbohydrate intake is of great importance to endurance athletes
who train for durations of longer than 90 minutes per day to replenish
muscle and liver glycogen levels. However, each gram of glycogen
requires extra water to be stored and may inhibit performance in
training or events shorter than 90 minutes. generally, individuals need
carbohydrate intake of 6 to 10 g/kg daily to restore muscle and liver
108 Buford
glycogen levels, but athletes training for periods longer than 90
minutes may require 8 to 10 g/kg/day (1 4).Infact,Fallowfieldand
Williams (15) determined that even when isocaloric diets were
consumed a high carbohydrate (8.8 g/kg) diet was s ignificantly
better at maintaini ng running time than a low carbohydrate
(5.8 g/kg) diet. Benef its vary a mong in dividua ls, howev er, and
some may experience gastrointestinal problems on a high carbohy-
drate diet; t heref ore, it is important for athletes to de ter mine w hat
works bes t for them.
Once the total grams of protein and carbohydrate have been
determined, multiply each factor by 4 to find the total number of
calories from each of the respective substrates. Once this step is
completed, subtract the number from the total energy needs deter-
mined earlier. The remainder of the necessary calories then come
from fat. Divide the fat calories by 9 to determine the total number
of fat grams to be consumed per day.
Although fats are the last macronutrient to be prescribed in the diet,
they are not simply throw-away calories. It is not the unimportance of
fats but, rather, the importance of carbohydrates and proteins that
makes fat the final consideration. In fact, high fat diets (35% kcal)
have been reported to enhance endurance performance in some
athletes (7). However, although fat is a significant fuel source for
many endurance or ultra-endurance athletes due to the ‘carbohydrate
sparing effect,’ fats are not in short supply and a high-fat diet inhibits
high intensity training and reduces endurance because glycogen stores
are limited. In addition, per unit of oxygen, fats are less efficient than
glucose at providing energy. The effects of a high fat diet also vary
among individuals, so caution should be used in recommending one.
Caution must be taken, however, not to restrict fat to a poin t where
lipolysis and fat oxidation are inhibited as well (16).
Once the macronutrient intake is determined based on body
weight and activity recommendations, the percentage of each of
the fuels should be compared to the original percentage goals.
Because the daily recommendations are ranges, they should be
reconciled with the percentages. For example, if the levels of 9 g/kg
for carbohydrate and 1.4 g/kg for protein break down to 80%
carbohydrate, 12% protein, and 8% fat, they need to be adjusted
to lower the carbohydrate intake and increase the fat (and possibly
protein slightly).
Macronutrient Intake for Physical Activity 109
3.3. Case Study
Ellen is an endurance athlete who comes to you for diet counsel-
ing. She is 27 years old, 5 ft 4 in. (163 cm) tall, and weighs 121 lb
(55 kg). During her training, she performs well at the beginning of
her sessions, but she feels fatigued sooner than she would like or
expect. She trains 5 or 6 days per week for 90 minutes per session at a
7 mph pace. She informs you that she consumes 2197 calories per
day with 302 g of carbohydrate, 83 g of protein, and 73 g of fat.
You inform Ellen that she first needs to consume more calories.
Based on her RMR (1356 kcal), exercise (918 kcal), other physical
activity (200 kcal), and thermogenesis (124 kcal), you inform her that
her calorie intake during regular training periods should be 2498 kcal.
The added calories should help her to improve her endurance.
In addition, you inform her that her current carbohydrate intake
is only 54% of her diet and should be closer to 65% to 70%. You
recommend that she begin to consume daily 440 g of carbohydrate,
77 g of protein, and 48 g of fat. This diet will provide her with 8.0
and 1.4 g/kg of carbohydrate and protein, respectively, while main-
taining a 70.5/12.3/17.2 carbohydrate/protein/fat ratio. However,
you inform her that some research has shown the beneficial effect of
a high fat diet in some individuals. Therefore, if the current high
carbohydrate diet does not work for her, she may consider increas-
ing dietary fat and reducing carbohydrate intake.
You inform her that this diet should help maximize muscle
glycogen stores while still providing enough fat for oxidation and
protein for contractile protein repair. After beginning this new diet,
Ellen discovers that her ability to maintain intensity during the ends
of her workouts improves, and she feels more ready to train properly
for her competitions.
4. NUTRIENT TIMING
One of the hottest topics in the sports nutrition field is the concept
of ‘nutrient timing.’ Nutrient timing suggests that it is not merely
what you eat and how much but also when. To build lean mass
properly, replace glycogen stores, or simply maximize athletic per-
formance, one needs to be conscious of the proper time to ingest
food or macronutrient supplements. Not only is the timing an issue
110 Buford
in terms of proper metabolic usage, but improper timing can also
cause gastrointestinal or psychological discomfort. In general, pre-
and postexercise supplements are preferred to be in liquid form to
limit discomfort to the gastrointestinal tract.
Aside from improving performance, the primary nutritional goal
for endurance athletes is to maximize (pre) and replenish (post)
glycogen stores. For many years, endurance athletes have used
‘carbohydrate loading’ as a tool for increasing muscle glycogen
stores. Variations of carbohydrate loading regimens exist, but load-
ing requires several days of high carbohydrate intake combined
with tapered exercise the week before competition. Yet endurance
athletes should not forget about the importance of fats as a fuel
either. For muscle glycogen to be spared during long-duration
endurance training, fats must be metabolized preferentially to gly-
cogen. Depending on the intensity of exercise, carbohydrate supple-
mentation immediately before or during exercise may inhibit
lipolysis due to insulin increases. Fat oxidation seems to be inhibited
by carbohydrate intake during lower intensity exercise (45%
VO
2
max) but not during moderate intensity exercise (17,18).In
contrast, increased dietary fat appears to increase lipolysis and fat
oxidation during exercise (19). Therefore, it may be advisable to
consume carbohydrate prior to moderate to high intensity exercise
so muscle glycogen is maximized but to consume small amounts of
fat prior to low intensity exercise to increase fat oxidation.
To maximize glycogen replenishment after exercise, it is necessary
to ingest a carbohydrate supplement immediately after and every
2 hours (up to 6 hours) following exercise (20). In addition, adding
protein to the carbohydrate supplement appears to increase glycogen
storage by acting synergistically on insulin secretion (21).Restoring
the glycogen levels properly after exercise allows proper recovery and
supports the next day’s training or competition.
For resistance training athletes, the goals are to increase amino
acid uptake and anabolic hormone release to enhance protein synth-
esis as well as to replenish glycogen stores. At present, it appears that
providing protein and/or carbohydrates immediately before and
after resistance exercise may provide the optimal environment for
enhanced muscle growth (22). Whereas consumption of protein
(23) or carbohydrate (24) following exercise has been shown to
increase protein synthesis, the combination of the two has shown
Macronutrient Intake for Physical Activity 111
even gr eater success be fore and after exercise (25,26). The pro-
tein–carbohy dr ate combinat ion consume d prior to and a fter a
workout has also been shown to increase growth hormone levels
significantly (27,2 8). In addition, it currently appears that con-
suming the postexer cis e supple ment a s soon as possib le is ex tre -
mely i mportant and more effective than waiting for extended
periods (22,29) .
Research in the area of nutrient timing and its connection with
athletic performance is greatly expanding. As more research is com-
pleted, further information on the proper timing of macronutrient
intake will most certainly come to light.
5. MAINTAINING OPTIMAL HEALTH DURING
TRAINING AND COMPETITION
One of the most overlooked aspects of nutrition is the role of
macronutrients in maintaining proper health during training and/or
competition. Poor nutritional status plays a major role in the devel-
opment of upper respiratory tract infections (URTIs), the most
common health risk limiting physical activity. Several other factors
including physical and mental stress, training intensity, injury, and
environmental status (e.g., exposure to damp locker rooms) have
also been linked to URTI development (Fig. 1) (30,31). Athletes
with extremely rigorous training schedules put themselves at risk for
Fig. 1. Factors contributing to the incidence of infection in athletes. Adapted
from Gleeson (30).
112 Buford
infection, and the risk is greatly increased with improper macronu-
trient nutrition (32). URTIs can greatly disrupt the quality of
training or competition as well decreasing the quality of life for the
individual. Specifically, infections with certain pathogens can cause
appetite suppression, malabsorption of and increased need for
nutrients, and increased loss of endogenous nutrients (33).
In the public media, much attention is focused on micronutrients
such as vitamin C and the B vitamins. However, deficiencies in
protein and carbohydrate play a major role in immune dysfunction.
Less is known about the contribution of fat to the immune response
with exercise. Protein is essential for rapid cell replication and pro-
duction of immunoregulatory proteins such as immunoglobulins,
acute-phase proteins, and cytokines (33). Carbohydrate feeding is
also necessary for reducing the inflammatory response to exercise,
including increased cortisol, catecholamines, and cytokine produc-
tion. In fact, there is significant evidence that carbohydrate feeding
during exercise is the best supplement for preventing immune dys-
function (34,35). Although often overlooked, the role of proper
macronutrient nutrition in immune function is critical to proper
performance and should be examined when infections are occurring.
6. CONCLUSION
Proper macronutrient nutrition is part of the basis of any success-
ful training and competition program. Prior to using nutritional
supplements, athletes must take care to design their diet properly
for their health in addition to making it ‘sport-specific.’ A proper
nutritional design is as essential to success as a well tailored exercise
program. The athlete must not only meet the body’s need for
calories but also meet specific needs for carbohydrates, protein,
and fat. A proper, macronutrient-balanced diet can help manage
body weight and provide the energy necessary for training and
competition while at the same time promote a healthy immune
system. In addition, it is now known that not only are the amounts
of calories and individual macronutrients important but the timing
of nutrient intake is as well. Each of these factors plays a critical role
in ‘sport-specific eating’’.
Macronutrient Intake for Physical Activity 113
6.1. Nutritional Considerations for the Vegetarian Athlet e
6.1.1. JEAN JITOMIR
Although little long-term experimental research has been con-
ducted on vegetarian athletes, the available evidence suggests that
these athletes can carefully plan their diets to obtain adequate
energy and nutrient consumption (36). Ovo (only eggs included),
lacto (only dairy products included), or ovo-lacto (both eggs and
dairy are included) vegetarians are at minimal risk for macronutri-
ent deficiencies. On the hand, vegan athletes, who avoid all animal
products, must carefully plan their diets to maintain optimal athletic
performance and general health (36).
6.1.2. E
NERGY
The three macronutrients—protein, carbohydrate, fat—provide
energy in the diet and have countless essential functions. Additionally,
the combined macronutrient energy contribution determines
whether an athlete maintains, loses, or gains weight. Athletes should
consult with dietitians and coaches to determine an intake that
satisfies energy needs and prepares the athlete for competition.
An athlete’s energy requirements vary widely based on athletic
event, training level, sex, and individual metabolism, among many
others. Hence, a broad energy intake recommendation is not
appropriate.
6.1.3. P
ROTEIN
The amount of protein required for an athlete is somewhat
controversial. The American recommended daily allowance
(RDA) value indicates that a protein intake of 0.8 g/kg is sufficient
for most of the population; however, sports nutrition experts advo-
cate a higher intake for athletes. Based on the RDA, a 50 kg (110 lb)
athlete requires only 40 g protein/day. The American College of
Sports Medicine (ACSM) recommends 1.2 to 1.4 g/kg/day for
endurance athletes and 1.6 to 1.7 g/kg/day for power athletes (37).
Because vegans eat only plant proteins, which are of lower quality
than animal proteins, the RDA for the general population may not
provide adequate levels of the essential amino acids. A vegan athlete
would likely benefit from consuming protein at the top of the
recommended range to ensure that essential amino acids are con-
sumed in adequate quantities. For example, a 50 kg vegan athlete
114 Buford
consuming protein at 1.7 g/kg should consume 85 g/day. Good
vegan sources of protein include soy products, beans, nuts, and
nut flours. These protein sources, in combination with the grains
eaten on a vegan diet, provide complete and adequate protein for the
vegan athlete.
Lacto-ovo vegetarians should also strive to meet the ACSM
guidelines. However, high quality protein is easily accessible with
the inclusion of dairy and egg products.
6.1.4. C
ARBOHYDRATE
According to the ACSM, athletes require 6 to 10 g of carbohy-
drate/kg/day (37). Glycogen is an important source of fuel for all
athletes but especially endurance athletes; carbohydrate consump-
tion in the higher range of the recommendation ensures maximal
glycogen storage. As such, an endurance athlete may benefit from
8 to 10 g of carbohydrate/day, depending on the level of training.
The 50 kg athlete consuming 8 g/kg/day should consume 400 g. A
nonendurance athlete requires less energy and may choose to con-
sume 6 g/kg/day.
It is particularly important to include carbohydrates before
exercise to maintain glucose levels throughout training. Either a
high-carbohydrate meal 3 to 4 hours before training or a low-car-
bohydrate meal about 1 hour before training is appropriate (37).
Additionally, a source of carbohydrate should be consumed within
30 minutes of exercise completion to replace lost glycogen. The
postworkout carbohydrate meal should contain at least 1.5 g/kg,
or 75 g, for the 50 kg athlete. Clearly, an athlete must consume a
substantial amount of total daily carbohydrates soon before and
after exercise (36). Carbohydrate sources are abundant in the vege-
tarian diet and include grains, beans, vegetables, and fruit. Fast-
absorbing carbohydrates (e.g., ripe bananas) are good choices
before and immediately after workouts.
6.1.5. F
AT
The ACSM recommends a moderate dietary fat intake of 20% to
25% of the total daily energy intake (37). Furthermore, a fat intake
lower than 15% of total energy from fat is not recommended by the
ACSM, as some fats are essential and adequate dietary fat is needed
to digest and transport the fat-soluble vitamins. Considering the
50 kg female athlete on a 2500 calorie diet, fat intake of 62 g/day
Macronutrient Intake for Physical Activity 115
provides the remainder of her energy requirements when she also
consumes 85 g of protein and 400 g of carbohydrate. A fat intake of
62 g/day provides about 22% of total energy as fat.
Additionally, athletes should consume dietary fat sources rich in
essential fats; nuts, fish, and oils are good choices. Saturated and
trans fats from cheese, meats, and processed foods harm long-term
health and do not provide essential fats.
6.1.6. C
REATINE SUPPLEMENTATION
Creatine supplementation has ergogenic e ffects for power ath-
letes who depend on quick bursts of energy or sports performance;
this category of athletes includes sprinters, weightlifters, and
many oth ers. Athletes who eat meat m ay obtain an additional
gram of crea tine each day from th e diet in addition to endogenous
production. Vegetarians do not obtain creatine from the diet
and have l ower intramuscular creatine l evels than nonve getarians .
Research has provided evidence that creatine supplementation
is particularly efficacious for vegetarian power athletes (38,39).
In fact , one study that compa red creatine s uppleme ntation in
vegetarians and nonvegetarians showed a greater increase in muscle
phosphocreatine, total creatine, type II fiber area, lean tissue
mass, and total work performed in the vegetarian group (39).
Even so, it is still recommended that athletes consult with coaches
to determine the appropriateness, safety, and dosage before taking
a dietary supplement.
As detailed above, vegetarian and vegan diets can, with careful
planning, fuel an athletic body for optimal performance.
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The quality of vegetarian diets to meet nutritional needs and support peak performance among athletes continues to be questioned. Appropriately planned vegetarian diets can provide sufficient energy and an appropriate range of carbohydrate, fat and protein intakes to support performance and health. The acceptable macronutrient distribution ranges for carbohydrate, fat and protein of 45–65%, 20–35% and 10–35%, respectively, are appropriate for vegetarian and non-vegetarian athletes alike, especially those who perform endurance events. Vegetarian athletes can meet their protein needs from predominantly or exclusively plant-based sources when a variety of these foods are consumed daily and energy intake is adequate. Muscle creatine stores are lower in vegetarians than non-vegetarians. Creatine supplementation provides ergogenic responses in both vegetarian and non-vegetarian athletes, with limited data supporting greater ergogenic effects on lean body mass accretion and work performance for vegetarians. The potential adverse effect of a vegetarian diet on iron status is based on the bioavailability of iron from plant foods rather than the amount of total iron present in the diet. Vegetarian and non-vegetarian athletes alike must consume sufficient iron to prevent deficiency, which will adversely affect performance. Other nutrients of concern for vegetarian athletes include zinc, vitamin B12 (cyanocobalamin), vitamin D (cholecalciferol) and calcium. The main sources of these nutrients are animal products; however, they can be found in many food sources suitable for vegetarians, including fortified soy milk and whole grain cereals. Vegetarians have higher antioxidant status for vitamin C (ascorbic acid), vitamin E (tocopherol), and ß-carotene than omnivores, which might help reduce exercise-induced oxidative stress. Research is needed comparing antioxidant defences in vegetarian and non-vegetarian athletes.
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The present study examined the effects of dietary manipulations on six trained runners. The percent energy contributions from carbohydrate, fat, and protein were 61/24/14,50/38/12, and 73/15/12 for the normal (N), fat (F), and carbohydrate (C) diets, respectively. Expiratory gases and blood responses to a maximum ([latin capital V with dot above]O2max) and a prolonged treadmill run were determined following 7 d on each diet. Free fatty acids (FFA), triglycerides, glycerol, glucose, and lactate were measured. Dietary assessment of subjects' N diet indicated that they were consuming approximately 700 kcal[middle dot]d-1 less than estimated daily expenditures. Running time to exhaustion was greatest after the F diet (91.2 +/- 9.5 min, P < 0.05) as compared with the C (75.8 +/- 7.6 min, P < 0.05) and N (69.3 +/- 7.2 min, P < 0.05) diets. [latin capital V with dot above]O2max was also higher on the F diet (66.4 +/- 2.7ml[middle dot]kg-1[middle dot]min-1, P < 0.05) as compared with the C (59.6 +/- 2.8 ml[middle dot]kg-1[middle dot]min-1, P < 0.05) and N (63.7 +/- 2.6 ml[middle dot]kg-1[middle dot]min-1, P < 0.05) diets. Plasma FFA levels were higher P < 0.05) and glycerol levels were lower (P < 0.05) during the F diet than during the C and N diets. Other biochemical measures did not differ significantly among diets. These data suggest that increased availability of FFA, consequent to the F diet, may provide for enhanced oxidative potential as evidenced by an increase in [latin capital V with dot above]O2max and running time. This implies that restriction of dietary fat may be detrimental to endurance performance. (C)1994The American College of Sports Medicine
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J Physiol 2001 August 15: 535(1): 301–11(1) Age-associated loss of skeletal muscle mass and strength can partly be counteracted by resistance training, causing a net synthesis of muscular proteins. Protein synthesis is influenced synergistically by post-exercise amino acid supplementation, but the importance of the timing of protein intake remains unresolved. (2) The study investigated the importance of immediate (P0) or delayed (P2) intake of an oral protein supplement upon muscle hypertrophy and strength over a period of resistance training in elderly males. (3) Thirteen men (age 74 ± 1 years; body mass index (BMI), 25 ± 1 kg m- 2 (means ± SEM)) completed a 12-week resistance training program (three times per week) receiving oral protein in liquid form (10 g protein, 7 g carbohydrate, 3 g fat) immediately after (P0) or 2 h after (P2) each training session. Muscle hypertrophy was evaluated by magnetic resonance imaging (MRI) and from muscle biopsies and muscle strength was determined using dynamic and isokinetic strength measurements. Body composition was determined from dual-energy X-ray absorptiometry (DEXA) and food records were obtained over 4 days. The plasma insulin response to protein supplementation was also determined. (4) In response to training, the cross-sectional area of m. quadriceps femoris (54.6 ± 0.5–58.3 ± 0.5 cm2) and mean fiber area (4047 ± 320–5019 ± 615 μ m2) increased in the P0 group, whereas no significant increase was observed in P2. For P0 both dynamic and isokinetic strength increased, by 46 and 15%, respectively (P P
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Plasma characteristics at high pressure YBa2Cu3O7−δ reactive magnetron sputtering were investigated with a probe technique and in situ film resistance measurements. The experimental features of probe measurements in oxygen plasma are discussed. Electron energy distribution is the sum of two Maxwell distributions with kTe ≈ 1.5 eV and kTe ≈ 0.3 eV. N2O addition to a gas mixture results in the generation of negative ions with a density virtually equal to the density of positive ions. The energies of ions, impinging the film surface under film biasing, are discussed in collisionless and drift approximations. Low energy ion bombardment of the film surface at temperatures ≈ 400 °C results in a reduction of film oxygen content. © 1997 American Institute of Physics.
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Prolonged exercise and heavy training are associated with depressed immune cell function. To maintain immune function, athletes should eat a well-balanced diet sufficient to meet their energy, carbohydrate, protein, and micronutrient requirements. Consuming carbohydrate during prolonged strenuous exercise attenuates rises in stress hormones and appears to limit the degree of exercise-induced immune depression. Recent evidence suggests that antioxidant vitamin supplementation may also reduce exercise stress and impairment of leukocyte functions. Further research is needed to evaluate the effects of other antioxidants and dietary immunostimulants such as probiotics and echinacea on exercise-induced immune impairment.