Enteral Nutrition Support Therapy for AdultsManual of Clinical Nutrition Management B- 39 Copyright © 2013 Compass Group, Inc.
and have a greater immunosuppressive effect, eicosapentaenoic acid metabolizes into less
immunosuppressive prostaglandins and leukotrienes. A study has shown the beneficial effects of omega-
3 fatty acids on the length of hospital stay and the infection rate following burn injury (26). In another
study, fewer gastrointestinal and infectious complications occurred in patients who received a formula
rich in fish oils when compared to patients who received a standard polymeric formula (27). Enteral
supplementation with omega-3 fatty acids has beneficial effects in the treatment of acute respiratory
distress syndrome (ARDS). In a study of 146 patients with ARDS, patients who received enteral formula
supplemented with omega-3 fatty acids (eicosapentaenoic acid) and gamma-linolenic acid (an omega- 6
fatty acid) had significant improvements in oxygenation, lower ventilation variables, fewer days of
ventilator support, and shorter stays in the ICU when compared to controls (28). According to both AND
and ASPEN guidelines, critically ill ARDS patients and those with severe acute lung injury may be placed
on an enteral formulation characterized by an anti-inflammatory lipid profile (eg, omega-3 fish oils,
borage oil) and antioxidants based on a comprehensive review of studies (Grade II) (3,5). Formulas containing arginine: Arginine is a conditionally essential amino acid during stress due to the
greater utilization of the urea cycle. Arginine is important in immune function and wound healing and is
commonly found in immune-enhancing and wound-healing enteral formulas. The immune-enhancing
properties of arginine include effects on the production and maturation of T lymphocytes and natural
killer cells (29,30). Arginine may be useful in treating inflammatory diseases and acquired
immunodeficiency syndrome, and it enhances collagen formation in wound healing (31,32). Although
studies have demonstrated positive outcomes of arginine supplementation, other studies have associated
arginine-containing formulations with an increased risk of mortality as compared to standard enteral
formulas in severely septic ICU patients (5). The mechanism proposed for this adverse effect was
hemodynamic instability caused by the conversion of arginine to nitric oxide in patients with severe
sepsis (6). More research is needed to determine the optimal dose, timing, and specific patient criteria
prior to the use of arginine supplemented formulas (3,5). (See the discussion of immune-enhancing
enteral formulations for suggested patient criteria.)
Formulas containing glutamine: Classified as a nonessential amino acid, glutamine is the primary
oxidative fuel for rapidly dividing cells, such as enterocytes and leukocytes. During stress or injury, the
metabolic demand for glutamine can exceed the capacity of skeletal muscle to release it (33). A fall in
glutamine concentration is associated with atrophy of the intestinal mucosa, impaired immune function,
and decreased protein synthesis (29). Substantial research has been completed in the past decade on the
effects of glutamine in enhancing small-intestine growth and repair from injury. Glutamine is not present
in standard parenteral formulas, and it is present in only small amounts in enteral formulas (16).
Formulas that contain intact proteins contain some bound glutamine. Although most research has
involved parenteral glutamine, one study demonstrated that patients who received glutamine-rich
enteral formula had significantly reduced hospital costs due to the prevention of secondary infections,
when compared to patients who received isoenergetic control formula (34). However, other studies have
found no effect with glutamine supplementation (3,35,36). The optimal amount and form of oral glutamine
required to achieve beneficial results is still unknown (3). Dosage and safety studies have found that 20 to
40 g/day of glutamine supplementation is safe and well tolerated by adults (37). According to ASPEN and
SCCM,the addition of enteral glutamine to an enteral nutrition regimen (not already containing
supplemental glutamine) may be considered in burn, trauma, and ICU patients with multiple medical
conditions or comorbidities (5 ) A review of studies found that additional glutamine is usually provided in
two or three divided doses that yield 0.3 to 0.5 g/kg body weight per day.” (5). The Academy of Nutrition
and Dietetics does not support this recommendation due to limited evidence supporting enteral
glutamine (Grade III) (3). Glutamine supplementation is contraindicated in patients with hyperammonemia,
hepatic failure, or renal failure due to excess ammonia production (4). Enteral glutamine should not be
added to an immune-modulating formulation already containing supplemental glutamine (5).
Formulas containing branched-chain amino acids (BCAA): Formulas supplemented with BCAA have
primarily been used for patients with hepatic failure in an attempt to improve the ratio of BCAA to
aromatic amino acids and prevent or improve hepatic encephalopathy. The use of BCAA-supplemented
enteral formulas has not been validated because studies have provided mixed results. A randomized
study found that BCAA supplementation reduced hospital admissions and improved nutritional status in
patients with advanced liver disease when compared to a standard formulation; however, there was no
difference in encephalopathy scores between the two groups (38). The routine use of BCAA-enriched
formulas is not recommended (15). Considering the limited evidence to support these formulations, the
ASPEN guidelines for nutrition therapy in liver disease restrict the use of BCAA-enriched formulas to