Dietary strategies to augment post-prandial muscle protein accretion

Young and elderly show differences in skeletal muscle mass. Aging is
accompanied by a loss of skeletal muscle mass, which is a consequence of an
imbalance between muscle protein synthesis and breakdown rates. Muscles consist
of proteins. These proteins consist again of several building blocks: the amino
acids. Due to our nutrition, which contains proteins and amino acids, building
blocks are available for muscle protein synthesis. Our nutrition is an
important stimulus of muscle synthesis. Previous research indicated that the
anabolic stimulation is impaired in elderly after the intake of small amounts
of protein or amino acids. In this study we would like to investigate whether
the muscle protein synthesis in elderly is improved after addition of other
nutrients to a standard protein drink. Two considered nutrients are
carbohydrates and leucine. The main part of our meals consist of carbohydrates.
The combination of protein and carbohydrates stimulates the release of the
anabolic hormone insulin. This hormone stimulates the muscle protein synthesis.
Intake of protein with carbohydrates could possilby increase the stimulation of
muscle protein synthesis. Leucine is an essential amino acid which is also able
to stimulate the muscle protein synthesis.
It has not yet been investigated whether the muscle protein synthesis in
elderly is improved after the intake of a normal meal-like amount of protein in
combination with leucine. Furthermore, it is unknown whether muscle protein
synthesis is improved after the combined intake of a normal meal-like amount of
protein with carbohydrates. In addition, it remains to be established whether
the effect on muscle protein synthesis after a combined intake of protein and
carbohydrates differs between young and elderly. This would possibly explain
the differences in skeletal muscle mass.

The objective of this study is to determine whether the intake of protein with
extra leucine or extra carbohydrates added results in an improved muscle
protein synthesis compared to the intake of only protein in elderly.

48 Males will participate in this study. Twelve males in the age of 70-85 years
will receive a drink containing only protein. Twelve other males of the same
age, will receive a protein drink with leucine added. Another 12 males will get
a drink with the same amount of protein and extra carbohydrates added. In
addition, a group of 12 young males (18-30 year) will get the same drink with
protein and carbohydrates. Using the blood samples and muscle biopsies it will
be possible to determine the muscle protein synthesis after intake of the test
drink.
In total, this study consists of one pre-testing session of 4 hours and one
test day which will take 6* hours, minimal 7 days after the pre-testing
session. Due to the possible impact on the protein metabolism of a warm meal
the day before the test day, the subjects receive a warm meal. In additon, we
will ask them to complete a dietary record 48 hours before the test day.

Intake of a protein drink with or without carbohydrates or leucine.

The risks involved in participating in this experiment are minimal. Insertion
of the catheters in a vein is comparable to a normal blood draw and the only
risk is of a small local hematoma. This is the same for the muscle biopsy. The
incision made for obtaining the muscle biopsy will heal completely within two
days. Possibly, the subject might have a dull feeling in his leg when the
effect of the anaesthetics is gone. The muscle biopsies will be performed by an
experienced physician. The test beverages contain only normal nutritional
ingredients dissolved in water, and will be flavoured with vanilla flavour;
for this reason intake of the test drink does not form any health risks.
One CT scans will be performed on each subject. The level of radiation emitted
during a CT scan is minimal since only single-slice scans will be taken and
only measurements at the lower extremity (at the level of mid-thigh) will be
performed. The exact radiation level is maximally 0.052 mSv.