Enteral formulas and feeding methods in adults

A range of commercial enteral formulas are available, with varying amounts of energy and protein, other macronutrients, electrolytes and fibre. Enteral formulas can be nutritionally complete, and most are gluten free and very low in lactose. Management of enteral nutrition support should be supervised by an accredited practising dietitian experienced in such care.

Standard polymeric enteral formulas are available in concentrations of 1.0, 1.2 to 1.25, 1.5 and 2.0 kcal/mL. The osmolarity increases as the concentration increases, so concentrated formulas can be more difficult to tolerate. Specialised formulas (eg low protein, high protein, low electrolyte) are available for specific medical conditions.

In most circumstances, polymeric enteral formulas are recommended. Rarely, adult patients require protein predigested into dipeptides or tripeptides (semi-elemental or extensively hydrolysed formulas) or even amino acids (elemental formulas).

The main methods for enteral feeding are:

• Continuous—formula is given via a pump at a specific rate (eg 80 mL/hour) for most of the day (eg 20 to 24 hours). This method is often used in the acute hospital setting when enteral feeding is started, or in patients who are unable to tolerate large volumes at a time or have a transpyloric or jejunal tube.
• Intermittent—formula is given over 24 hours, with intervals of rest (eg 4 hours feeding, followed by 2 hours rest), usually via a pump. Overnight feeding is a variation of this, allowing time off tube feeding during the day. This method is often used for supplemental enteral nutrition support to encourage eating during the day.
• Bolus—a specific volume of formula is given at various times during the day (eg 250 mL, 5 times daily), usually using gravity feeding. This method most resembles eating meals. The rate of administration can be varied. This method is often used for patients who require long-term feeding, particularly via gastrostomy tubes at home.

The type of tube may determine the formula and feeding method used. Patients with gastric tubes (eg gastrostomy, nasogastric) can usually tolerate various formulas and feeding methods. Patients with tubes into the small intestine (eg jejunostomy, nasojejunal) should have continuous feeds with a lower osmolarity formula. Choice of feeding method also depends on various other factors, including the patient’s tolerance, nutritional requirements, comorbidities, activity level, lifestyle and preference. For information on enteral feeding in diabetes, see Enteral feeding for adults with diabetes.