The effect of meat texture on promoting muscle protein synthesis in elderly humans

Aging is accompanied by a decline in skeletal muscle mass. This loss is a
consequence of an imbalance between muscle synthesis and muscle break down. The
muscle synthesis is strongly stimulated by the intake of food, especially by
protein. It seems that this process is declined in elderly people in comparison
to young persons. Especially the protein digestion and absorption rate from
food in the intestine plays an important role. Proteins stimulate the muscle
growth due to the supply of the building blocks, the amino acids. After a meal,
the availability of amino acis in the blood is essential for the regulation of
muscle growth. An increase in this availability is possible by using proteins
which will be digested fast. The concept of fast and slow digested proteins
have been extracted from research with milk proteins. This research has been
shown that fast digested proteins cause a faster absorption of the amino acids,
a faster deliverly to the muscle and as a consequence the amino acids are
faster incorporated in the muscle. Whether this concept is also applicable to
other protein sources in the daily nutrition, like meat, is still unknown. Meat
is an impotant protein source for many adults and is almost daily consumed.
Various meat product got their own different meat structure. This structure
might be completive for the protein absorption rate from meat and the
subsequent muscle protein synthesis. However, scientific evidence for this
proposition is still lacking.

The objective of this study is to test whether meat structure plays an
important role in protein digestion, to maximise the amino acid availability
and to stimulate the muscle protein growth in elderly people.

Twelve subjects between the age of 65-85 years will be selected for this study.
Each person participates in two test days, in which the effect of meat
structure (intact or minced: beef steak or minced beef, respectively) on
protein digestion and muscle protein synthesis will be tested. The two test
days will be separated by 14 days. A cross-over design will be used to prevent
the between-persons-variation in chewing and gastrointestinal tract
functionality. Furthermore, the food intake preceding the test day will be
standardised by using a food diary: each subject will fill in a food diary 48
hours before the first test day, so that he will be able to use exactly the
same diet before the second test day. Additionally, we will use a constant
stable amino acid isotope infusion during the test days to determine the
protein breakdown, synthesis and muscle synthesis (as previously described in
MEC 02-060, MEC 03-090, MEC 05-028 en MEC 06-3-064).

Intake of beef meat, intact or minced: Beef steak of minced beef, respectively.

The risks involved in participating in this experment are minimal. Insertion of
the catheters in a vein in the arm and on the hand can cause a small local
hematoma. This is the same for the muscle biopsy. The incision made for
obtaining the muscle biopsy willheal completely in two days. Possilbly, the
subject might have a dull feeling in his leg when the effect of the anaesthesia
is gone. The muscle biopsies will be performed by an experienced physician. The
labeled amino acids tracers applied in this experiment are not radioactive and
are completely safe. The vacuum-packed and pre-weighed meat meals are normal
food products and have been cleared for human consumption.

Total time investment is 20 hours per subject.
General screening: 3 hours.
Test day: 2 x 8 1/2 hour.