Proteins help build and maintain tissues in the body. Muscle, organs, and the immune system are made up mostly of protein. The protein source in a formula can come from milk, soy or other types of food protein.

Common types of protein sources in tube-feeding formulas can include:

• Whey protein
• Casein
• Soy protein

Whey and casein are the main forms of protein found in cow's milk and in breast milk, while soy protein comes from soybeans. Casein is a slowly digested protein and whey protein is a quickly digested protein. Whey protein empties from the stomach more quickly than either casein or soy, and may be helpful for a child who has reflux or vomiting.

Forms of protein: Protein can be provided in varying forms, including intact (whole protein), partially hydrolyzed (broken down or pre-digested), or as free amino acids (the smallest form of broken-down protein).

• Intact protein: This means that the protein has not been broken down at all. This is the type of protein that is used in most standard formulas and is appropriate for children who have normal digestion.
• Partially hydrolyzed protein: This means that the protein is broken down into smaller pieces called peptides, which are easier to digest than intact proteins. Formulas made with partially hydrolyzed protein are appropriate for those who have difficulty with digestion or absorption of a standard formula. Signs of these types of problems may be vomiting, diarrhea, bloating, excessive gas, fussiness or a bloated stomach. Formulas with partially hydrolyzed proteins can also be used in children with normal digestion if your healthcare professional feels the need.
• Free amino acids: Amino acids are the "building blocks" of proteins, and are the smallest forms of proteins that can be broken down into. Free amino acid formulas are used for children who have very severe digestive and absorption problems, cow’s milk protein allergy or have severe allergies to whole food proteins. If a child cannot tolerate a formula with partially broken-down protein (e.g., your child has severe diarrhea, vomiting, bloating, gas or pain), a free amino acid formula may be needed.

Carbohydrates are the main source of energy for the body. The body breaks down carbohydrates into simple sugars, which are absorbed from the digestive tract into the bloodstream. The hormone insulin then moves these simple sugars from the blood into the cells of the body, where they can be used as a source of energy. Tube-feeding formulas contain carbohydrates that are easily digested and absorbed in the digestive tract.

Some formulas include different types of fiber. Simple sugars such as sucrose and glucose can be used to flavor and improve the taste of a formula for a child who will be drinking it, but these ingredients can also increase the formula's osmolality, which is a measure of the number of soluble particles per kilogram of water. The osmolality of a tube-feeding formula is an important consideration because it can affect your child's ability to tolerate it. A formula with a higher osmolality compared to normal body fluids will draw water into the digestive tract, and extra water in the digestive tract can cause nausea, cramping, bloating, and diarrhea.

Fiber is added to some tube-feeding formulas to help maintain normal bowel function, to improve movement of foods through the digestive system, and to manage diarrhea or constipation.

Fiber can be either insoluble or soluble. Insoluble fiber may also be referred to as "non-fermentable" fiber. This type of fiber helps with digestion by providing bulk in the stool to help maintain healthy digestive tract function, including helping to manage diarrhea and constipation. Soluble fiber is also referred to as "fermentable" fiber. Certain levels of soluble fiber in the diet can help manage blood sugar levels, and lower LDL and total cholesterol.

Some soluble fiber is referred to as "prebiotic fiber," which helps to promote a healthy balance of beneficial microorganisms in the digestive system. Both types of fiber are not digested and absorbed by the body, but instead help to move food through the digestive system, promoting regular bowel movements and reducing the risk of constipation.

Fats are a major source of calories, and help the body to use certain vitamins. Corn and soybean oil are commonly used fat sources in tube-feeding formulas, and canola and safflower oils may also be used. The majority of fats in the diet are triglycerides. The triglycerides in tube-feeding formulas are either medium-chain triglycerides (MCT) or long-chain triglycerides (LCT). MCT can be more efficiently absorbed than LCT and are sometimes added to formulas for children with digestive problems. LCTs are essential to health, but are more difficult to digest. MCTs are more easily absorbed than LCTs, which is why they are sometimes added to formulas for children with digestive problems.

Fish oil is added to some tube-feeding formulas. This type of oil is a rich source of omega-3 fatty acids, particularly DHA and EPA, which help to support the immune system. Omega-3 fatty acids are known to have a role in reducing inflammation and supporting the health of the digestive system. Fish oil supplements have also been found to support the health of the respiratory system and heart.