promote recovery and improve muscle integrity by ingesting ideal nutrient
combinations at optimal times.
The search for ways to enhance performance and muscle growth through
dietary manipulation is not new. Questions abound regarding the optimal amounts
of protein, carbohydrate and fat needed to boost performance, while nutrition
recommendations based on training goals are plentiful. A new twist on current
science is a concentration on when, rather than just what, athletes
should consume before, during and after a training session to optimize their
performance and recovery.
articles emphasizing various phases of muscle growth and glycogen repletion have
been popping up in the fitness literature. The hormonal responses to exercise
and the dips and peaks of the anabolic players (insulin, testosterone and
others) have become a hot topic in sports nutrition. John Ivy, PhD, and Robert
Portman, PhD, described nutrient timing as the “future of sports nutrition”
in their 2004 book Nutrient Timing (Ivy & Portman 2004). Other lay
publications and online articles have tagged nutrient timing as evidence for the
efficacy and sales of various supplements.
While the leap to
nutritional supplementation may be unnecessary, understanding when and what to
eat around a training regimen holds merit.
The science to support
the concept of nutrient timing may not be novel, but the focus on when and what
to eat may help to further educate bodybuilders, athletes and active individuals
about the vital relationship of proper nutrition to performance and recovery.
What Is Nutrient
Simply put, nutrient
timing means being mindful of when to eat, rather than just what to eat. Its
premise is to support optimal performance during a training session, provide all
that is needed for muscle growth, exploit glycogen replenishment after activity,
and follow a diet that promotes growth and repair around the clock. It is based
on data supporting variances in hormonal release throughout the day and in
response to exercise (see “Endocrinology 101,” below). Ivy and Portman have
divided the day into three phases to illustrate the concept.
Phase 1: Energy Phase
The nutrient timing
cycle begins with the workout: the energy phase. This phase is marked by the
athlete’s need for sufficient energy to allow muscle contraction. Ivy and
Portman emphasize the importance of nutrient delivery and of sparing
carbohydrate and protein, limiting immune suppression, minimizing muscle damage
and setting the stage for faster post-workout recovery. Glucose, derived from
glycogen (its stored form in liver and muscle) or blood glucose, is an essential
fuel source for activity. Reliance on glucose increases directly with training
intensity (Wildman & Miller 2004). Glucose depletion is indicated by a
decrease in time to fatigue during activity-much to an athlete’s dismay (Robergs
& Roberts 1997). The need for carbohydrate ingestion during activity depends
on the intensity, duration and type of exercise, in addition to the pre-exercise
carbohydrate status and foods consumed, and the degree of training (Wildman
& Miller 2004).
recommendations for carbohydrate intake during the energy phase or during
activity are difficult to nail down. The authors of Nutrient Timing encourage
some carbohydrate ingestion, preferably of foods with a high glycemic index (see
“glossary of Terms,” below) in order to increase glucose uptake by the
muscle and thus to increase muscle glycogen synthesis. Research supports the use
of carbohydrate during activity, but the amount and form required are still
foggy. Murray et al. evaluated the administration of carbohydrate beverages
during intermittent cycling (1987). The results showed that the carbohydrate
drinks produced performance improvements and higher plasma glucose levels,
without differences among the types of carbohydrate administered (Murray et al.
1987). A scientific review by Jeukendrup concluded that performance benefits
could be found when subjects ingested as little as 16 grams (g) of carbohydrate
per hour-with the type consumed appearing to have little effect on the benefit
Ingestion of protein
during the energy phase may be advantageous when provided in addition to
carbohydrate. Ivy et al. investigated the use of carbohydrate-protein
supplementation during endurance activity (2003). Their findings revealed a
benefit to including carbohydrate and protein, over just carbohydrate, at
20-minute intervals during 3 hours of cycling at varying intensities on three
separate occasions. The differences could not be attributed to differences in
insulin responses, however, leaving the researchers curious about the
improvement in performance (Ivy et al. 2003). Irrefutable recommendations for
ingesting protein during exercise remain elusive owing to lack of research.
Phase 2: Anabolic
This “window of
opportunity” phase is estimated as the 45 minutes following a training session
or competition. The unique qualities of this phase include the body’s need to
replete itself and its improved ability to do so. Ivy and Portman summarize the
characteristics and goals of this phase as (1) a shift from catabolism to
anabolism; (2) enhancement of muscle blood flow; (3) replenishment of glycogen
stores; (4) repair and growth of tissue; and (5) reduction of muscle damage and
bolstering of the immune system (2004). Immediately following exercise, a myriad
of factors create an environment for glycogen repletion and muscle tissue growth
and repair. Among these factors is the enhanced activity of anabolic hormones
(see “Endocrinology 101”), including insulin, testosterone, growth hormone
and insulin-like growth factor-1 (IGF-1).
After exercise, the
body is primed to replenish its glycogen stores, and protein repair and
synthesis are required (Levenhagen et al. 2001). Insulin sensitivity is improved
because of an increase in glucose transport into the cells via a specific
glucose carrier (GLUT-4), and the activity of the enzyme glycogen synthase is
increased to promote glycogen synthesis (Richter et al. 1982). Ingesting
carbohydrate after exercise increases the amount and rate of glycogen storage (Zawadzki
et al. 1992). A combination of protein and carbohydrate replenishes muscle
glycogen more rapidly than does carbohydrate alone (Ivy et al. 2002). Levenhagen
et al. showed that early post-exercise ingestion of protein and
carbohydrate not only replenished muscle glycogen but also enhanced accrual of
whole-body and leg protein, suggesting an exercise-induced effect by insulin
The rate of glycogen
repletion may also be enhanced by increasing the carbohydrate content. Van Loon
et al. administered carbohydrate to trained cyclists at 30-minute intervals
following exercise; synthesis rate was faster in subjects who received 1.2 g per
kilogram (kg) of body weight each half-hour than in those who received 0.8 g/kg
(2000). In this same study of cyclists, van Loon et al. showed that a mixture of
wheat hydrolysate, free leucine and phenylalanine with carbohydrate increased
insulin response by 88% over carbohydrate only (2000). The increase in insulin
sensitivity appears to be best exploited by feeding carbohydrate and protein at
2-hour intervals following activity (Ivy et al. 2002). It is unclear exactly how
long the benefits persist, but Richter et al. found they were present after 4
The second objective
in the anabolic phase is to create an environment conducive to muscle repair and
growth. Chandler et al. provided experienced weightlifters with water,
carbohydrate, or a carbohydrate and protein supplement immediately and 2 hours
after a session (1994). The carbohydrate and protein supplement produced higher
levels of insulin and growth hormone, creating a more favorable environment for
growth. All three supplements blunted testosterone, however, and showed no
difference in effect on IGF-1. For reasons not related to the increase in
insulin (as with the aforementioned data), protein supplementation immediately
following exercise also aids in muscle hypertrophy (Esmarck et al. 2001).
Esmarck et al. provided elderly men with a protein supplement immediately or 2
hours following a weightlifting session; they showed significant muscle
hypertrophy when supplementation was immediate, but not when it was given 2
hours later (2001).
Phase 3: Growth Phase
The growth phase can
best be summed up as the remainder of the day after training. In the initial
hours of this phase, the body is still in the post-exercise mode. Because
glycogen repletion perseveres, part of the goal during this phase is to exploit
this process for as long as possible. In addition, enhancing muscle protein
synthesis and muscle growth is important. MacDougall et al. determined that
protein synthesis is elevated by 50% at 4 hours following resistance training,
and by 109% at 24 hours, with a return to baseline at 36 hours (1995). In
addition, further evidence supports consuming protein and carbohydrate prior to
exercise to enhance post-exercise protein synthesis (Tipton et al. 2001).
Feeding muscle growth and repair, as well as maintaining optimal glycogen
stores, is imperative during the growth phase. Achieving a positive nitrogen
balance during this time by providing adequate protein will aid in muscle gains
Before engaging in conversation about eating in
response to the ebb and flow of hormones, it is helpful to understand the
hormonal players and their response to exercise. The following chart—adapted
from Robergs and Roberts’ Exercise Physiology, Exercise, Performance, and
Clinical Applications (William C. Brown 1997) and McArdle, Katch &
Katch’s Exercise Physiology: Energy, Nutrition, and Human Performance (Lippincott
Williams & Wilkins 2001)—provides a list of hormones and their major
functional responses to exercise.
increases with moderate to intense exercise and it functions to increase
increases with moderate to intense exercise and it functions to increase fat
breakdown, heart rate and glycogen breakdown
increases with prolonged exercise and it functions to increase
gluconeogenesis and glycogen breakdown
increases with intense, prolonged exercise promotes fatty acid and protein
breakdown; and it functions to decrease glucose uptake
decreases with exercise and it functions to increase glucose, amino acid and
fatty acid uptake
increases with exercise and it functions to control muscle size; increase
red blood cells; decrease body fat
Hormone (GH) increases with exercise and it functions to stimulate tissue
growth; mobilize fatty acids for energy; decrease glucose uptake; increase
stimulated by GH and it functions to stimulate growth
Applying Timing to
If you can combine an
understanding of when food should be consumed with a knowledge of what
and how much to ingest, devising a successful nutrition program for
your clients’ training can be easy! The following summary can help you educate
clients (by training type)—beginning with the what and how much, and
leading into the when.
Training Type: Endurance
What and How Much to
Eat. It is recommended that the endurance-trained
athletic client (exercising 90+ minutes most days) should consume approximately
22–25 calories per pound (lb) of body weight (BW) every day, with carbohydrate
intake being 3.0–4.0 g per lb of body weight (g/lb BW) daily (Kundrat 2005).
For example, an active 140 lb athlete needs approximately 3,080–3,500 calories
per day to maintain weight and 420–560 g of carbohydrate. Diets consistently
high in carbohydrate-versus those high in fat—have been shown to delay time to
exhaustion during exercise (Kleiner 2001).
Stipulating how many
g/lb BW of protein an athlete needs per day is difficult. An in-depth review of
protein requirements for endurance athletes by Tarnopolsky recommends 0.5 g/lb
BW to 0.7 g/lb BW-increasing with the level of training (2004). For instance, an
endurance-trained 140 lb athlete needs 70–98 g of protein per day (e.g., a
3-ounce serving of lean meat, poultry or fish; an egg or a quarter cup egg
substitute; a half cup cooked beans or lentils; and 2 tablespoons peanut
butter-along with the recommended 6–11 servings of breads, cereals and pastas;
2–4 fruits; 3–5 vegetables; and 2–3 milk servings).
When: Pre-Exercise. Susan Kundrat, MS,RD, LD, owner of Nutrition on the Move in Urbana,
Illinois, and author of 101 Sports Nutrition Tips, recommends assessing
what is best tolerated before a workout or competition and building the meal or
snack around high-carbohydrate foods. At 3 hours prior to a competition or
training session, 1.4 g/lb BW is the maximum level of carbohydrate, with 0.5
g/lb BW at 1 hour prior (Kundrat 2005). Planning
a meal or snack before
exercise is especially important, chiefly if exercising early in the morning.
See “Pre and Post-exercise Snack Ideas for Combining Carbs and Protein,”
below, for examples.
When: During Activity.
Based on the foregoing, as little as 16 grams
of carbohydrate per hour appears to provide performance benefits (Jeukendrup
2004). Other sources recommend upward of 30–60 g per hour (Kundrat 2005).
Therefore, an exact number of grams cannot be determined. Wildman and Miller
contend that drinking 600–1,200 milliliters (ml) of a 6%–8% carbohydrate
sports drink per hour will help maintain blood glucose during
When: Post-exercise. Refueling with carbohydrate after a workout is essential. An
absolute recommendation is to consume at least 50 g of carbohydrate and 10–15
g of protein with fluid within 15–30 minutes after the session (Kundrat 2005).
Relative to body weight, 0.5 g/lb BW of carbohydrate is recommended in the first
30 minutes post-exercise and again every 2–3 hours thereafter (Wildman &
Miller 2004). The combination of protein and carbohydrate can be found in a
sports drink plus an energy bar; apple juice and a peanut butter sandwich; a
milkshake; yogurt and juice; or 2 cups of corn flakes and 1 cup of low-fat milk.
Training Type: Resistance Training
What and How Much. Bodybuilders are rightfully not shy about consuming calories. A
range of 20–23 calories/lb BW per day is recommended for growth (Kleiner
2001). Kundrat advises all athletes working toward muscle growth to combine
their workout with 3,000–4,000 extra calories per week when trying to maximize
muscle growth. Whether the goal is to build muscle or enhance muscle definition,
protein is important for the maintenance, repair and construction of muscle.
However, contrary to popular practices, a diet extremely high in protein is not
protein vary depending on the source and research. Kleiner advises approximately
0.6–0.8 g/lb BW of protein throughout the day (2001). For a 130 lb woman, this
means 78–104 g of protein per day. For vegetarians, increasing that to 1.0
g/lb BW will help ensure that proper amounts of the essential amino acids are
obtained (Kleiner 2001). Ivy and Portman recommend 0.9–1.25 g/lb BW of protein
per day based on nitrogen balance data (see “Glossary of Terms,” below),
despite criticisms regarding the accuracy of using this method for determining
daily protein needs (Phillips 2004). A review by Phillips points out that the
average reported protein intake among strength athletes is 0.94 g/lb BW,
indicating that athletes are meeting their needs. Carbohydrates (70% of total
calories) are especially important to those performing challenging resistance
When: Pre-Exercise. The pre-exercise meal for a resistance training exerciser should
include carbohydrate and protein (approximately 50 g carbs and 14 g protein) 11/2–2 hours before
training (Kleiner 2001). Athletes might try a pita pocket with hummus or a bagel
with low-fat cream cheese and some dried fruit. A sports drink just before the
workout can provide the extra stamina required to “push” that weight (Kleiner
When: During Activity.
Carbohydrate ingestion during a heavy
resistance workout can help sustain muscle glycogen levels (Haff et al. 2003).
Haff et al. investigated the effects of carbohydrate ingestion during resistance
training, and although muscle glycogen concentration was protected, no
improvements in performance were noted (Haff et al. 2000). The amount of
carbohydrate to consume during resistance training has not been defined;
however, as mentioned previously, drinking 600–1,200 ml of a 6%–8%
carbohydrate sports drink per hour can be beneficial (Wildman & Miller
2004). However, bodybuilders should be careful not to over-consume calories if
weight is a concern (Kleiner 2001).
To date, there is
little evidence that protein ingestion during a workout offers an athletic edge.
Recommendations still lean toward the importance of ingesting protein
post-exercise for anabolism and repair.
When: Post-exercise. Immediately following a workout, carbohydrates and protein need to
be consumed to replenish depleted carbohydrate stores and help with muscle
repair. Post-exercise recommendations are similar to those for the
endurance-trained athlete. Glycogen needs to be replenished, and carbohydrate
combined with protein is the most effective choice.
Nutrient Timing for Everyday Exercisers
timing appears best suited for competitive athletes, its strategies can benefit
everyday exercisers as well. Proper fuel stores (carbohydrate and protein) can
enhance any workout, and the anabolic characteristics of the post-exercise phase
for dedicated step,
indoor cycling and boot camp enthusiasts alike. Advising clients to consume a
balanced snack 2–3 hours prior to exercise and to consume a carbohydrate- and
protein-containing snack or meal following the session helps them advance their
workout, enhance their glycogen stores and recover successfully. As suggested by
Kleiner, calories may be unnecessary during the workout if weight loss or
maintenance is the objective (2001).
Pre and post-exercise snack ideas for combining carbs and protein
• energy bar and 8-ounce sports drink
• 2 slices whole-grain toast and 2
tablespoons peanut butter
• orange and 1/2 cup low-fat cottage cheese
• 1 cup cooked oatmeal with 1/4 cup raisins
• 1 cup yogurt and 1/4 cup granola
• 2-egg omelet with 1 cup fresh vegetables, 1
whole-wheat English muffin
• string cheese and 1 ounce pretzels
• 1/4 cup nuts and a medium apple
• hard-boiled egg and 1/2 whole-wheat bagel
• whole-wheat pita and 1/2 cup canned tuna
• 1/4 cup soy nuts and 1 banana
• 1/4 cup sunflower seeds and 1 cup orange juice
• 3 ounces boiled or grilled chicken breast
and 1 cup cooked white rice
Balance Is Key
Eating a balanced,
varied diet with adequate protein and carbohydrate will enhance training
sessions and workouts; and taking advantage of the hormonal milieu of anabolic
players following activity will promote recovery and improve muscle integrity.
As with previous sports nutrition recommendations, the take-home message is that
the active body benefits from proper nutrition.
Glossary of terms
synthesizing in metabolism
glucose from non-carbohydrate sources, such as amino acids and glycerol
the cell membrane used to transport glucose to the cell interior
degree and duration of blood glucose elevation in response to ingestion of a
carbohydrate-containing food relative to a standard 50-gram amount of
glycogen to glucose
from protein sources in the diet in relation to nitrogen excreted (If
excretion exceeds ingestion, there is a negative nitrogen balance
[associated with infection, trauma]; if ingestion exceeds excretion, there
is a positive nitrogen balance [associated with pregnancy, muscle growth].)
Jenna A. Bell-Wilson,
PhD, RD, LD, is assistant professor in medical dietetics at the Ohio State
University. She completed her doctorate in exercise science at the University of
New Mexico. Dr.Bell-Wilson, a contributing editor for IDEA Fitness Journal, writes and speaks frequently in the area
of nutrition and exercise.
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