Casein in milk as a functional ingredient for the prevention of sarcopenia

The progressive loss of skeletal muscle mass with aging, or sarcopenia, has a
major impact on our healthcare system due to increased morbidity and greater
need for hospitalization and/or institutionalization. One way to prevent
skeletal muscle loss is to improve dietary intake of the elderly.
The ingestion of milk proteins is known to strongly stimulate muscle protein
synthesis and inhibits protein breakdown, resulting in a positive net protein
balance and, as such net muscle protein accretion. This anabolic effect clearly
depends on the quality and the quantity of the protein source. The major
proteins in bovine milk are casein (~80%) and whey protein (~20%). In their
isolated forms, these proteins greatly differ in their digestion and absorption
kinetics. Isolated whey protein has been characterized as a rapidly digested
protein leading to a pronounced, rapid, but transient peak in plasma amino acid
levels. On the other hand, isolated casein is a slowly digested protein that
results in a slower, moderate, but more prolonged increase in plasma amino acid
availability when compared to whey protein. When casein enters the stomach and
is brought to a pH of 4.6 or lower, casein precipitates, whereas whey protein
remains in solution and does not clot. At present, casein is regarded as a less
anabolic protein in the elderly, due to its slower digestion and absorption.
However, these studies have all provided their subjects with isolated casein.
It is currently unknown how casein behaves when it is ingested in its natural
form as a constituent of whole bovine milk. There are several indications that
casein may behave quite differently when it is ingested within the matrix of
normal milk. Besides whey protein and casein, normal skimmed milk also contains
lactose, salts, minerals and vitamins. These other components may modulate
gastric pH and/or emptying and thus the bioavailability of casein derived amino
acids and therefore the subsequent post-prandial muscle protein synthetic
response. The results from this study will provide important insight in the
development of novel nutritional intervention strategies to counteract the
age-related loss of muscle mass.

To compare the digestibility, bioavailability and subsequent muscle protein
synthetic response to casein, with casein protein provided in an isolated
manner versus casein in a milk matrix, in healthy elderly subjects

Randomized, single blind, parallel study

one group (n=16) will consume a test beverage of 600 mL containing 20 g of
intrinsically labeled casein in water, and the other group (n=16) will consume
a beverage of the same volume containing 20 g of intrinsically labeled casein
in milk matrix

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 a small local hematoma. This is also true for muscle biopsies. Muscle
biopsies will be taken through a small (5 mm) incision, following local
anesthetics of the skin and muscle fascia, and will heal completely. Muscle
biopsies will only be obtained by an experienced physician. The labeled,
non-radioactive amino acids tracers that will be infused intravenously are
produced according to GMP standards and are safe for human use.