An elemental diet is a diet that proposes the ingestion, or in more severe cases use of a gastric feeding tube or intravenous feeding, of liquid nutrients in an easily assimilated form. It is usually composed of amino acids, fats, sugars, vitamins, and minerals. This diet, however, lacks whole or partial protein due to its ability to cause an allergic reaction in some people.

The elemental diet is used mainly in the treatment of individuals with Crohn's disease as a form of nutritional therapy. Crohn's disease is a type of inflammatory bowel disease causing inflammation of any area of the gastrointestinal tract and is able to occur in people of all ages, but often diagnosed in people between the ages of 20 and 30. The most common indication of having Crohn's is blockage of the intestine, and sores and ulcers around the area of the affected tissue. This includes the bladder, vagina, rectum, and anus. Other problems may also include skin problems, arthritis, and inflammation of the mouth or eyes.

Nutritional problems that result from Crohn's are due to inflammation of the small intestine that cause diarrhea. This leads to malabsorption of important nutrients in the small intestine, causing malnutrition, fever, fatigue, and weight loss.

The elemental diet consists of a mixture of essential amino acids with non-essential amino acids, fat, and sugars. Water-soluble vitamins, fat-soluble vitamins, and electrolytes are often added. The elemental diet is commonly introduced over a period of three days to patients, successively increasing in strength on each day to reduce the likelihood of diarrhea and abdominal colic. It can be given orally or through nasogastric tubes if patients are intolerant to the liquid.

Patients are restricted of all foods; however, certain exceptions in some patients are made for tea and coffee (without milk) and given Vivonex ^{[clarification needed]} as the elemental diet. Other elemental diets such as Elental can be used that provide similar results. The elemental diet provides a high nitrogen source for patients from amino acids and acts as a medical bypass. Because the diet consists of the individual dietary components of food in their simplest form, the body does not have to do work to digest them. They prevent the food from "reacting" with the gut, preventing the occurrence of symptoms. The resulting positive nitrogen balance and alterations in the bacterial flora of the gut are likely to have beneficial effects in patients, helping to alleviate the symptoms of Crohn’s. However, due to the diet's consisting of fully broken down amino acids, the digestive loading is shifted from the gut to the liver. As such, liver function (via blood tests) should be monitored.

The elemental diet is also used to treat Small Intestinal Bacterial Overgrowth (SIBO) with a 14-day elemental diet showing 80% efficacy and a 21-day elemental diet showing 85% efficacy.

As beneficial as the elemental diet is in patients, there are a few disadvantages. A common disadvantage is the taste of the elemental diet. Many patients are unable to tolerate the taste, even if the diet is flavoured, and choose to receive it through intragastric administration. Possible nausea and diarrhea can result from the high sugar content which can also complicate hyperglycaemia in patients with pre-existing diabetes.