http://www.eurekalert.org/pub_releases/2004-02/aps-cos022504.php

Carbohydrates offer some help in muscle protein synthesis, but not
enough for the desired effect

(February 25, 2004) - Bethesda, MD – A visit to the meat counter at
any supermarket is proof positive that a good number of Americans are
avoiding carbohydrates and consuming high levels of protein and fat,
in accordance with the Atkins diet. This carbohydrate-free, fat- and
protein- rich diet is for those seeking immediate weight loss, which
means most of us.

But what do others, such as weight lifters and callisthenic
enthusiasts, do about carbohydrates? Their goal is muscle preservation
and strengthening, but for years, different theories have been offered
about the effectiveness of carbohydrates in maintaining an appropriate
muscle protein balance. A new study may lead to a truce in the debate
at the nation's gymnasiums, and those dedicated to resistance training
may finally have an answer as to whether carbohydrates have a positive
role in muscle development.

Resistance exercise -- also called strength training -- increases
muscle strength and mass, bone strength, and the body's metabolism.
The different methods for resistance training include free weights,
weight machines, calisthenics and resistance tubing. When using free
weights, dumbbells, and bars stacked with weight plates, you are
responsible for both lifting the weight and determining and
controlling your body position through the range of motion.

The body's net muscle protein balance (i.e., the difference between
muscle protein synthesis and protein breakdown) generally remains
negative in the recovery period after resistance exercise in the
absence of nutrient intake, i.e., the muscle's protein is breaking
down complex chemical compounds to simpler ones. However, it has been
demonstrated that infusion or ingestion of amino acids after
resistance exercise stimulates muscle protein synthesis. Furthermore,
as little as six grams of essential amino acids (EAA) alone
effectively stimulates net protein synthesis after a strenuous
resistance exercise session.

The body's response to the six grams of EAA does not appear to differ
when 35 grams of carbohydrates are added. This reflects the
uncertainty of the independent effects of carbohydrates on muscle
protein metabolism after resistance exercise. Additionally, it is
unclear how carbohydrate intake causes changes of net protein balance
between synthesis and breakdown and how it relates to changes in
plasma insulin concentration.

Interpretation of the response of muscle protein to insulin is
complicated by the fact that a systemic increase in insulin
concentration causes a fall in plasma amino acid concentrations, and
this reduced amino acid availability could potentially counteract a
direct effect of insulin on synthesis. A past study found that the
normal postexercise increase in muscle protein breakdown was slowed by
insulin, thus improving net muscle protein balance. However, whereas
local infusion of insulin may effectively isolate the effect of
insulin per se, the response may differ from when insulin release is
stimulated by ingestion of carbohydrates.

Accordingly, a new study set out to investigate the independent effect
of carbohydrate intake on muscle protein net balance during recovery
from resistance exercise. The authors of "Effect Of Carbohydrate
Intake on Net Muscle Protein Synthesis During Recovery from Resistance
Exercise," are Elisabet Børsheim, Melanie G. Cree, Kevin D. Tipton,
Tabatha A. Elliott, Asle Aarsland, and Robert R. Wolfe, all from the
Department of Surgery, Metabolism Unit, Shriners Hospitals for
Children-Galveston, University of Texas Medical Branch, Galveston, TX.
Their findings appeared in the February 2004 edition of the Journal of
Applied Physiology. The journal is one of 14 peer-reviewed scientific
journals published each month by the American Physiological Society
(www.APS.org).

Sixteen recreationally active and healthy subjects took part in the
study. At least one week before an experiment, subjects were
familiarized with the exercise protocol, and their one repetition
maximum, a maximum weight possible with a leg extension, was
determined. The subjects were assigned to one of two groups:
carbohydrate group (CHO; n = 8) or placebo group (n = 8). Subjects
were instructed not to exercise for at least 48 hours before an
experiment, not to use tobacco or alcohol during the 24 h before an
experiment, and not to make any changes in their dietary habits.

The two groups of eight subjects performed a resistance exercise bout
(10 sets of eight repetitions of leg presses at 80 percent of one
repetition maximum) before they rested in bed for four hours. One
group (CHO) received a drink consisting of 100 grams of carbohydrates
one hour after exercise; the placebo group received a noncaloric
placebo drink. Leg amino acid metabolism was determined by infusion of
2H5- or 13C6-labeled phenylalanine, sampling from femoral artery and
vein, and muscle biopsies from vastus lateralis, the lateral head of
quadriceps muscle of anterior (extensor) compartment of thigh.

Key findings of the study included:

Plasma glucose concentration was significantly increased in the
carbohydrate group until 210 min after intake of drink.

Plasma concentration of insulin reflected the changes in glucose
concentration. The drink intake did not affect arterial insulin
concentration in the placebo group, whereas arterial insulin increased
by several times after the drink in the CHO group.

Arterial phenylalanine (a common amino acid in proteins) concentration
did not change after intake of drink in the placebo group but
decreased and stabilized in the CHO group.

Net muscle protein balance between synthesis and breakdown did not
change in the placebo group but improved in the CHO group during the
second and third hour after the drink. The improved net balance in the
CHO group was due primarily to a progressive decrease in muscle
protein breakdown.

Conclusions:

This study is the first to compare net muscle protein balance (protein
synthesis minus breakdown) after carbohydrate ingestion with control
after exercise. The principal finding was that intake of 100 grams of
carbohydrates after resistance exercise improved muscle net protein
balance.

The findings from this research demonstrate that carbohydrates intake
alone can improve net protein balance between synthesis and breakdown.
In this work, the gradual improvement in net muscle protein balance
after carbohydrate intake was due principally to a progressive
reduction in breakdown. However, the improvement was small compared
with previous findings after intake of amino acids or amino acids and
carbohydrates.

The researchers conclude that intake of carbohydrates alone after
resistance exercise will modestly improve the anabolic effect of
exercise. However, amino acid intake is necessary for a maximal
response, one desired by most participating in resistance exercise
programs.

Source: February 2004 edition of the Journal of Applied Physiology.
The journal is one of 14 peer-reviewed scientific journals published
each month by the American Physiological Society (www.APS.org).

The American Physiological Society (APS) was founded in 1887 to foster
basic and applied science, much of it relating to human health. The
Bethesda, MD-based Society has more than 10,000 members and publishes
3,800 articles in its 14 peer-reviewed journals every year.