The manipulation of dietary protein intake on the anabolic response in healthy young men

Protein intake stimulates muscle protein synthesis rates, and this effect is
enhanced if physical activity is performed prior to food intake. Therefore,
from the standpoint of maximizing (or maintaining) skeletal muscle mass, it is
important to optimize the adaptive response to food intake. However, a paucity
of information is available describing the effects of prior meal feedings,
consisting of either high or low amounts of protein, on the subsequent
meal-induced stimulation of muscle protein synthesis rates. Of note, it is
necessary to determine the effects of ingesting a single high protein meal
versus an *adaptation* that may occur after habitual consumption of high, or
low, protein meals. An adaptation is certainly different in time-scale, but
also may involve splanchnic and skeletal muscle adaptations that may further
enhance, or decrease, the amino acid sensitivity of muscle protein synthesis
rates after protein ingestion. Thus, we wish to assess both the immediate acute
impact of a prior high protein meal on the subsequent stimulation of muscle
protein synthesis rates after protein intake and physical activity (Study 1),
and whether longer-term adjustments to the anabolic response to protein intake
occurs after habitual consumption of high or low protein intakes for 14 days in
healthy young men (Study 2).

STUDY 1: To investigate the impact of prior ingestion of a single high protein
meal on the normal obligatory increase of muscle protein synthesis rates after
protein intake and physical activity in healthy young men.

STUDY 2: To investigate the impact of a habitual (14 days) high or low protein
diets on the muscle protein synthetic response to dietary protein ingestion

parallel, randomized (for both study 1 and 2)

STUDY 1: Following unilateral resistance exercise, one group of subjects (n=12)
will consume high protein beverages, and the second group (n=12) will consume
isocaloric-matched carbohydrate beverages. The following morning, both groups
of subjects will consume 20 g of whey protein.

STUDY 2: One group of subjects (n=12) will consume a high protein diet for 14
days and the second group (n=12) will consume a low protein diet for 14 days.
The morning following the dietary intervention, both groups of subjects will
consume 20 g of casein protein.

The risks involved in participating in this experiment are minimal. Insertion
of the catheters is comparable to a blood draw and could result in a small
hematoma. We will take 9 and 15 blood samples (8 mL) during the experimental
infusion trials for Study 1 and 2, respectively. The total amount of blood we
draw is less than half the amount of a blood donation and will be completely
restored in approximately 1 month. Muscle biopsies will be taken under local
anesthesia by an experienced physician, but may cause some minor discomfort for
up to 24 h after completion of the procedure. The discomfort is comparable to
muscle soreness or the pain that may be experienced after bumping into a table.
In Study 1 participants will come to the university twice: 1 screening (2
hours) and 1 experimental trial lasting ~20 h, which also includes an overnight
stay at the laboratory. During the screening, we will perform a DEXA scan. DEXA
is a simple and non-invasive procedure. Three days prior to the experimental
trials, participants will need to record their diet in detail for estimation of
habitual protein intake. The labeled, non-radioactive amino acid tracers that
will be infused intravenously are produced according to GMP standards and are
safe for human use.
In Study 2 participants will come to the university for 2 main visits: 1
screening (2 hours) and 1 experimental trial lasting ~9 h. The same as study 1,
during the screening we will perform a DEXA scan and three days prior to the
experimental trials, participants will need to record their diet in detail for
estimation of habitual protein intake. Between the screening and the
experimental test day will be a 14 day period of complete dietary control and
subjects will visit the university every 2 days to collect/return the
prescribed food.
There is no direct benefit for the participants, only their contribution to
scientific knowledge that will provide the evidence base for the prescription
of exercise and nutritional strategies to improve the quality of life and
health across the life-span.