Enteral Nutrition Support Therapy for Adults
Manual of Clinical Nutrition Management B- 38 Copyright © 2013 Compass Group, Inc.
casein or soy protein isolate (15). Lactalbumin, whey, and egg albumin are also sources of intact proteins.
Formulas that contain intact proteins require normal levels of pancreatic enzymes for digestion and
absorption (15). Carbohydrate sources include corn syrup solids, hydrolyzed cornstarch, maltodextrin,
sucrose, fructose, and sugar alcohols. Carbohydrates provide 40% to 90% of total energy (15). The fat content
ranges from less than 10% to more than 50% of total energy. Common fat sources are corn oil and soybean
oil; however, safflower, canola, and fish oils are also used in enteral formulas (15). The osmolality of synthetic
formulas ranges from 270 to 700 mOsm/kg. Because a high incidence of lactase deficiency in illness is
presumed, lactose is not present in most synthetic enteral formulas (15).
Elemental or semi-elemental formulas: These formulas consist of hydrolyzed macronutrients. Protein is
present either as free amino acids (monomeric) or as bound amino acids in dipeptides or tripeptides
(oligomeric). Carbohydrate sources consist of oligosaccharides, sucrose, or both. Most monomeric formulas
are low in fat or contain a large percentage of medium-chain triglycerides (MCT) oil. These formulas are low
residue, hyperosmolar, and usually lactose free. They are indicated for patients with compromised
gastrointestinal function, such as patients who have acute pancreatitis (15) or persistent diarrhea (5).
Formulas with predigested nutrients should not be used for patients with normal digestion and absorption,
because they are unnecessary for these patients and cost more than standard intact (polymeric) nutrient
formulas.
Modular components: These products are individually packaged components that may be combined in
varying amounts to meet the patient’s individual nutritional needs. Examples include protein powders,
carbohydrate powders, MCT oil, fiber, and specific amino acids (eg, glutamine and arginine). Protein
powders, which provide 7 to 15 g of protein per serving, are the most commonly used modular additives, as
standard enteral formulations tend to have a high ratio of nonprotein energy to nitrogen (5,15). Modular
components may also be added to premixed formulas to enhance the intake of one or more macronutrients. If
modular components are added to premixed formulas, the preparation should follow the organization’s
Hazard Analysis and Critical Control Point Enteral Nutrition Plan (7).
Nutrient-Modified and Disease-Specific Formulas
Nutrient-modified and disease-specific formulas have been altered in one or more nutrients in an attempt to
optimize nutrition support without exacerbating the metabolic disturbances associated with various diseases.
Limited evidence is available regarding the efficacy and outcomes associated with the use of most disease-
specific enteral formulations (4). Standard enteral formulas are appropriate for most critically ill patients (3).
Disease-specific formulas are more expensive than standard enteral formula, and a dietitian should carefully
evaluate their potential benefit for an individual patient before recommending them. If such formulas are
used, the patient should be monitored and advanced to a standard formula as soon as possible (3).
Nutrient-modified formulas include:
Formulas containing fiber: Fiber is added to enteral formulas for a variety of potential health benefits
(17). Soluble fibers, such as guar gum, oat fiber, and pectin, are fermented to short-chain fatty acids, which
are easily absorbed by the gastrointestinal mucosa. Short-chain fatty acids, the preferred fuel for
colonocytes, help to increase mucosal growth and promote sodium and water absorption (17). It is
important to consider the type of fiber supplemented in the enteral formula. Soy polysaccharide an
insoluble fiber, and guar gum a soluble fiber are common types of fiber used in formulas. Soluble fiber
reduces the incidence of diarrhea, but studies of formulations supplemented with insoluble fiber have not
yielded the same results (5,15,18-20). ASPEN guidelines recommend avoiding the use of insoluble fiber
formulas in critically ill patients (5). It has also been suggested that both soluble and insoluble fiber
should be avoided in patients at high risk for bowel ischemia or severe dysmotility (5,15). Cases of bowel
obstruction from the use of these formulations have been reported (14,21,22). Enteral formulas containing
fiber generally provide 5 to 14 g/L, which is less than the recommended 20 to 35 g of fiber per day.
When a fiber formula is used, adequate free-water needs should be maintained and tolerance closely
monitored, especially for patients receiving larger volumes of fiber-containing formulas (eg, greater than
2 L per 24-hour period). Soluble fiber–containing formulas using guar gum are indicated in critically ill
patients when there are no contraindications for their use and the goal is to maintain a normally
functioning gastrointestinal tract and defecation pattern, or to manage diarrhea (Grade III) (3,5,23).
Formulas containing omega-3 fatty acids: The type and amount of fat in enteral formulas may affect
immune function (24-27). Fish oils, a rich source of omega-3 fatty acids, provide eicosapentaenoic acid.
Unlike omega-6 fatty acids, which are found in more common fat sources (eg, corn oil and soybean oil)