12 elderly (65-70 years of age) male subjects will be included and complete a double blinded cross-over study. They will be habituated for 21 days to either low or high protein intake (below 0.8 g/kg or above 1.5 g/kg, respectively). Following a 45 day washout period they will switch to the alternate group. At the end of each habituation period, the investigators will measure the appearance of labelled amino acids from milk proteins.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
TRIPLE
Enrollment
12
Participants are habituated to a high level of dietary protein intake for 21 days.
Participants are habituated to a low level of dietary protein intake for 21 days.
To investigate impact of habituated protein level
Institute of Sports Medicine Copenhagen
Copenhagen, Denmark
Abundance of milk protein-bound amino acid labels in blood protein.
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: After intake of milk proteins at time 0 (zero) the quantity of intrinsic labels D5-phe from whey and 15N-phe from casein will be measured in liver-synthesized blood protein at 240 min.
Time frame: Baseline to 240 min postprandial
Abundance of milk protein-bound amino acid labels in myofibrillar protein.
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: After intake of milk proteins at time 0 (zero) the quantity of intrinsic labels D5-phe from whey and 15N-phe from casein will be measured in myofibrillar protein at 240 min.
Time frame: Baseline to 240 min postprandial
Leg phenylalanine rate of disappearance and appearance, net balance.
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: From arterial and femoral venous blood samples obtained at baseline, 30, 60, 90, 120, 150, 180, 240 min phenylalanine tracer enrichments and concentrations as well as plasma flow will be measured.
Time frame: Baseline to 240 min postprandial
First pass splanchnic extraction of dietary protein-derived labeled phenylalanine.
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: From hepatic venous blood samples obtained at baseline, 30, 60, 90, 120, 150, 180, 240 min phenylalanine tracer enrichments and concentrations as well as plasma flow will be measured. Knowing the amount of ingested protein and labeled phenylalanine we can calculate the first pass splanchnic amino acid extraction.
Time frame: Baseline to 240 min postprandial
Whole body phenylalanine rate of disappearance and appearance, net balance.
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Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: From blood samples obtained at baseline, 30, 60, 90, 120, 150, 180, 240 min phenylalanine tracer enrichments will be measured.
Time frame: Baseline to 240 min postprandial
The myofibrillar protein fractional synthesis rate
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: From muscle biopsies obtained at baseline, 60 and 240 min the abundance of phenylalanine tracer bound in the myofibrillar proteins will be measured and the fractional synthesis rate will be measured within the first from baseline to 60 min and 240 min as well as from 60-240 min postprandial.
Time frame: Baseline to 240 min postprandial
Response of expression of proteins involved in muscle protein turnover
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: From baseline to 60 and 240 min after intake of the standardized meal after 21 days of habituation to either a high or a low dietary protein intake expression of signalling proteins related to protein turnover in the muscle will be measured by use of western blotting.
Time frame: Baseline, 60 min and 240 min postprandial
Urea production.
Related to the trials conducted after 21 days of habituation to either high or low protein in the diet: From blood samples obtained at baseline, 30, 60, 90, 120, 150, 180, 240 min urea tracer enrichments and concentrations will be measured. With this, and flow measurements, we can determine the rate of urea production.
Time frame: Baseline to 240 min postprandial
Nitrogen and creatinine excreted in urine
Related to the adaptation to the 21 day habituation period to either high or low protein in the diet as well as the response to the standardized trial meal: Nitrogen and creatinine content is measured in urine is collected for the last 24 h of the 21 day habituation period, as well as during the 240 min trial day and the remaining 20 hours of the trial day.
Time frame: 21 days post intervention, 240 min postprandial and 24 hours post the day 21 trial day
Fecal microbiota composition
Related to the adaptation to the 21 day habituation period to either high or low protein in the diet as well as the response to the standardized trial meal: The microbiota compositions, will be measured in fecal samples collected before the 21 day habituation period, after the 21 day habituation periode, as well as after the 240 min trial day
Time frame: Change from pre-intervention to 21 days and 22 days (21 intervention days habituation and the standardized trial meal on day 21)
Adaptation of expression of proteins involved in muscle protein turnover
Related to the adaptation to the 21 day habituation period to either high or low protein in the diet: Biopsies taken following the two 21 day habituation period will, by use of western blotting, be analysed for expression of signalling proteins involved in muscle protein turnover.
Time frame: After 21 days of habituation to either a high or a low dietary protein intake.