|
tein (e.g., 70 g per day vs. an ideal of
100 g) if the protein source is rich in the BCAAs.6 This would
be particularly beneficial for patients who require a protein-restricted
diet but are in a malnourished state. Similarly, patients who
need to restrict their fluid intake may benefit from an amino
acid formula enriched with BCAAs because it is difficult to give
sufficient protein without high volumes of free water. Hunter
et al.6 measured nitrogen utilization (protein synthesis and
oxidation rates) in patients with cancer cachexia who received
total parenteral nutrition (TPN) with an amino acid mixture containing
a normal concentration of BCAAs (19%) vs. an enriched diet (50%
BCAAs). Whole-body protein synthesis, breakdown, and albumin
synthetic rates were increased significantly with the BCAA-enriched
formula, strongly supporting the supposition of a benefit in
these patients. Each protein source contains similar amounts
of BCAAs (17% to 24%), with milk and whey (Promune) having the
highest concentrations (Table 2).
Arginine
Arginine is a conditionally essential amino
acid during times of stress.7 It appears to enhance immune function
by increasing the activity of natural killer cells and lymphokine-activated
cells. Hospitalized cancer patients undergoing major surgery
achieved a more positive nitrogen balance when their diet was
supplemented with 25 g of arginine, compared with a control group
receiving an isonitrogenous diet with glycine.
Arginine may also be beneficial to healthy
subjects. Healthy elderly subjects who received diets supplemented
with 17 g of free arginine had significantly enhanced wound hydroxyproline
content (an index of collagen deposition and wound healing) and
plasma insulin-like growth factor (IGF-1). This population typically
has depressed T-cell numbers and function and reduced serum IGF-1
levels. Soy has the highest amount of arginine of the proteins
listed in Table 2.
|
Glutathione
Description
Glutathione (g-glutamyl-cysteinyl-glycine,
GSH) is a tripeptide composed of cysteine, glutamine/glutamate,
glycine.8,9 Both cysteine and glutamate are found in greater
concentrations in whey protein compared with other high biological
value proteins (Table 2). Specifically, GSH contains cyst(e)ine
(the combination of cysteine and cystine when the contribution
of each is not precisely known). Cystine is the oxidized form
of cysteine. It also contains glutamate (glutamic acid), which
contains one molecule of nitrogen, in contrast to two in glutamine.
Both cysteine and glutamine are important
in the coordinated T-cell response of macrophages and lymphocytes.10-12
Cyst(e)ine is released from the muscle during catabolic stress;
stores of it can become depleted during long-term illnesses like
HIV infection.13 Cysteine, unlike cystine, is readily transported
into cells and is rate-limiting in the formation of GSH.14,15
Once cysteine concentrations are adequate, glutamine becomes
rate-limiting.16,17 Glutamine is also a predominant amino acid
in the skeletal muscle, and is rapidly lost during catabolic
stress. However, whey protein is rich in glutamate, which could
serve as a substitute for glutamine and could limit muscle protein
breakdown.
Glutathione is found in all mammalian cells
and provides the principal intracellular defense against oxidation
stresses such as superoxide anions, lipid peroxidases, and iron-generated
hydroxyl radicals.
Next
|
Back