Section 2 - Enteral formulas

Introduction

The selection of an enteral formula must be patient specific. The functioning and capacity of the GI tract, underlying disease states and patient tolerance must be assessed to determine which formula should be selected. Many formulas are very similar in composition, varying only slightly in nutrient content. It is important to be familar with the properties of commonly used enteral formulas.

Nutrient composition

Carbohydrate

Carbohydrate sources must be soluble, digestible and have a low osmolality. Commonly used carbohydrate sources include corn syrup solids, hydrolyzed cornstarch, maltodextrins and other glucose polymers. Some specialty formulas include various types of fiber, fructose, and fluctooligosaccarides. Simple sugars (sucrose and glucose) enhance the palatability of oral supplements but increase osmolality.

The percentage of total calories from carbohydrate varies from 30% to 90% depending on the condition for which the product was formulated. The majority of enteral nutrtion products do not contain lactose so should not be a concern in lactose-intolerant patients.

Lipids

Lipids provide an isotonic, caloric dense energy source. Corn and soybean oil are commonly used lipd sources in enteral formulas. Canola and safflower oils may also be found. These vegetable oils contain mostly long-chain triglycerides. They contribute essential fatty acids, limit osmolality, and enhance palatability.

Fat content of enteral formulas varies from 1% to 55% of total calories according to the formula's intended use. For example, products designed for pulmonary disease and glucose intolerance are high in fat, whereas products designed for intestinal malabsorption contain decreased amounts of total fat.

Medium-chain triglycerides (MCT) do not require bile salts or pancreatic lipase for absorption and may be used in patients with lipid malabsorption disorders. However, MCT oil does not contain essential fatty acids and may cause delayed gastric emptying, leading to poor tolerance.

Protein

Protein may be delivered as intact protein, partially digested protein, or free amino acids. Choice of product is based on the patient's disease state and the ability to absorb the protein. Commonly used protein sources include caseinates and soy protein isolates. Polymeric formulas contain these intact proteins. Oligomeric formulas contain enzymatically hydrolyzed casein or whey. Monomeric or elemental formulas contain free amino acids.

The protein content of formulas ranges from approximately 4% to 32% of total calories. Products designed for renal disease may contain virtually no protein, whereas stress and immune-enhancing formlas contain up to 80g/1000kcal.

Specialized enteral formulas may be enhanced with branch-chain amino acids, glutamine, or arginine.

Water

Caloric density of a formula is dictated by the amount of water contained in the formula. Formulas that provide 1 kcal/ml are approximately 85% water. Formulas that provide 2 kcal/ml are approximately 70% water.

Micronutrients

When provided in adequate volume, nutritionally complete products meet 100% of the RDA for vitamins and minerals. Howerver, the volume required to provide the RDA varies greatly among products from one to four liters. Also, be aware that some disease-specific enteral formulas are not nutritionally complete.

Fiber

Fiber is added to enteral formulas to improve stool consistency. The most commonly added fiber is soy polyscaccaride, an insoluble fiber. Other insoluble fibers are cellulose, hemicellulose, and lignans. Soluble fibers are guar gum, oat fiber, and pectin. The effectiveness of fiber-containing formulas in improving incidence or duration of diarrhea has not been proven. Fiber-containing formulas can create complications in patients who are fluid restricted or have delayed GI transit.

Formula categories

Presented here is one of many different schemes for classifying enteral nutrition formulas.

Enteral formula categories

Category	Subcategory	Characteristics	Indications
Polymeric	Standard	Similar to average diet	Normal digestion
	High nitrogen	Protein > 15% of total kcal	Catabolism Wound healing
	Caloric dense	2 kcal/ml	Fluid restriction Volume intolerance Electrolyte abnormalities
	Fiber containing	Fiber 5-15 g/L	Regulation of bowel function
Monomeric	Partially hydrolyzed	One or more nutrients are hydrolyzed. Composition varies.	Impaired digestive and absorptive capacity
	Elemental
	Peptide based
Disease-specific	Renal	Less protein, low electrolyte content	Renal failure
	Hepatic	High BCAA, low AA, low electrolyte content	Hepatic encephalopathy
	Pulmonary	Higher % of calories from fat	ARDS
	Diabetic	Low CHO	Diabetes mellitus
	Immune-enhancing	Arginine, glutamine, omega-3 FA, antioxidants	Metabolic stress Immune dysfunction

Special populations

Diabetes

• Maintain glucose levels between 100 - 220 mg/dL
• Give 30% of total kcal as fat
• Gastric atony and delayed emptying is typical in type 1 diabetes

Renal disease

• Fluid restriction (2 kcal/ml formula)
• Pre-dialysis= low protein (0.6 - 0.8 g/kg/day)
• Dialysis= standard protein (1 - 1.2 g/kg/day)

Pulmonary disease

• Calories: 20 - 30 kcal/kg
• Give 30% - 50% of total kcal as fat
• Protein: 1 - 2 g/kg

Hepatic disease

• High calorie intake (35 kcal/kg/day)
• If no encephalopathy, standard protein (1 - 1.2 g/kg/day)
• If encephalopathy, protein resteriction (0.6 g/kg/day)
• Sodium restriction if ascites or edema

Cardiac disease

• Avoid overfeeding
• Fluid restriction (2 kcal/ml formula)

Section 2 - Enteral formulas