A liquid diet is often used to treat or prevent malnutrition. Because liquid diets are usually high-calorie, they can also be used in inflammatory bowel disease (IBD) treatment to provide additional calories and to allow the bowel to rest and to heal.
There are also low-calorie liquid diets that serve as meal replacements for weight loss; however, these are not important in a medical context.
What is in a liquid diet?
As the name suggests, a liquid diet can be a liquid mixed with powder, or it may have a slightly mushy form. They contain proteins, carbohydrates, fats, and micronutrients. They typically are made of the following ingredients:
- Water or milk
- Cooking oil
- Modified starch
- Hydrolyzed protein
- Synthetic vitamins
When is a liquid diet necessary?
A liquid diet is typically needed when there is an increased need for nutrients. A liquid diet may be necessary for the following situations or with the following clinical diagnoses:
- Under- or malnourishment
- Serious infections or injuries
- Chewing and swallowing disorders
- After surgery
- Inflammatory bowel diseases
- Short bowel syndrome
- Metabolic disorders
- Multiple food allergies
- Chronic liver disease
- Renal insufficiency
Why are liquid diets used for IBD?
Acute IBD flare-ups are often accompanied by loss of appetite, pain, and severe diarrhea. As a result, many with IBD consume less food and have reduced nutrient absorption in the intestine. At the same time, a flare-up increases the_ basal metabolic rate_, or the amount of energy the body uses while at rest.
Chronic IBDs—especially Crohn's disease—often cause people to be underweight and malnourished.
Depending on the disease course, nutrient deficiencies may occur, particularly for vitamin B12, folic acid, and zinc. After severe diarrhea, there may be deficiencies in potassium, magnesium, calcium, and phosphate. Vitamin D deficiency is also common.
As a result of malnutrition, growth delays can occur, especially in children. In older patients, there is an increased risk of developing bone loss (osteoporosis).
How does a liquid diet affect IBD?
Studies have shown that nutrition therapy can support the healing of Crohn's disease by inducing and maintaining remission phases, or periods of time with fewer or no symptoms. For people with ulcerative colitis, nutrition therapy demonstrated no effect on the healing process. For both conditions, nutrition therapy should be given if being underweight or malnourished could lead to complications.
When is a liquid diet prescribed?
Before a liquid diet is prescribed, one's normal diet must first be adjusted to meet the specific nutritional requirements for the respective disease. If the adjustment of the normal diet is not possible or does not achieve the desired effect, a switch to a liquid diet is then considered. Depending on the condition, a liquid diet could also be prescribed as a supplement to one’s normal diet.
Before prescription of a liquid diet, an individual's personal nutritional requirements must be determined. If one's energy need is only slightly higher than their present intake, a normocaloric liquid diet is necessary, which contains the same amount of calories as normal food. If one's energy need is much higher than their present intake, a high-calorie liquid diet is prescribed.
How many calories are in a liquid diet?
Depending on the number of calories per milliliter, a distinction is made by energy density for liquid food:
- **Low-calorie: **up to 0.9 kcal/ml
- **Normocaloric: **1 kcal/ml
- **High-calorie: **more than 1.1 kcal/ml
There is also very high-calorie liquid food with up to 5 kcal/ml, which is offered in 120 ml bottles (up to 600 kcal/bottle). By contrast, the same amount of orange juice has approximately 50 calories, and the same amount of vanilla ice cream has around 165 calories. In order for an average person to gain 2.2 pounds per week, an additional 1,000 calories are planned per day.
Most energy consumed from a liquid diet is fat. Many products contain medium-chain fatty acids (MCFAs) for easy absorption of fats.
What are alternatives to a liquid diet?
With a liquid diet, patients continue to receive nutrition naturally through the mouth, throat, and gastrointestinal tract. If this is not possible, the patient receives food through a feeding tube into the stomach (enteral nutrition). In most cases, a nasogastric tube is inserted into the stomach via the nose. This allows for the preservation of the gastrointestinal tract, or enteral route.
Enteral nutrition brings food into the body that has already been broken down into its smallest components, allowing for a low molecular-weight diet. The upper part of the intestine can completely absorb all available nutrients, and the rest of the digestive system is relieved.
In rare cases, if it is not possible to absorb substantial nutrients via the digestive system, parenteral nutrition may be necessary. In this case, necessary nutrients are directly introduced into the bloodstream.
When is a liquid diet recommended? When is a gastric tube recommended?
Nutrition therapy helps to maintain normal body weight and to provide the body with sufficient nutrients. If solid food cannot adequately meet one’s energy needs with IBD, a liquid diet ingested orally or via a gastric tube are good options.
When an additional energy intake of less than 600 calories/day is required, liquid food ingested orally is appropriate. When additional energy of more than 600 calories/day is needed, a gastric tube is usually best.
Generally, artificial nutrition support must be taken into account when oral ingestion is or could be absent for more than 5 to 7 days.
Which liquid diet is recommended for IBD?
A fully balanced, high-molecular liquid diet is recommended in order to avoid suppression of the intestine's digestive work. High-molecular means that the food components have not yet been broken down. Many suppliers of liquid foods for IBDs also offer low-molecular liquids, in which the nutrients have already been broken down into their components and pre-digested.
There are also other liquids with a high proportion of MCFAs that the body can easily absorb. Some contain anti-inflammatory additives, such as glutamine or TGF-beta, yet studies to date have been unable to find any associated benefit.
Does a low-calorie liquid diet allow for weight loss?
In patients who are obese, the use of low-calorie liquid diets for weight loss is currently being tested. However, the implementation of these diets often fails because chewing is an important part of enjoying a meal. Chewing is satisfying and also regulates eating behavior. If you only consume liquid food without exact measurements, you can end up consuming more and still feeling hungry. When reducing caloric intake, the metabolism also slows down to save energy, in case weight is regained after stopping a liquid diet.
For example, side effects are also possible—especially in very low-calorie liquid diets—when proteins, carbohydrates, fats, vitamins, or minerals are lacking or unbalanced.
What do liquid diets taste like?
Savory liquid diets taste a bit like soup, as they usually contain pureed vegetables. However, the taste of a liquid diet is not comparable to a bowl of fresh soup.
Many prefer a sweet-tasting liquid diet. It is easier to create a normal taste experience with this kind of liquid food because many sweet foods, such as ice cream, pudding, and yogurt, already have a similar consistency. Sugar is also a good source of energy. The taste of sweet liquid food is usually fruity or milky, and popular varieties include chocolate, vanilla, and strawberry. Special flavors are created by adding an aroma.
Where can I buy liquid diets?
Liquid diets are available in various pharmacies, drugstores, and supermarkets. When buying, you should make sure that it is a certified medical product tailored to your personal needs.
Bischoff S, Koletzko B, Lochs H, Meier R, and the DGEM Steering Committee. S3 guideline of the German Society for Nutritional Medicine (DGEM) in cooperation with the Society for Clinical Nutrition in Switzerland (GESKES), the Austrian Working Group for Clinical Nutrition (AKE) and the German Society for Gastroenterology, Digestive and Metabolic Diseases (DGVS ). Aktuel Ernahrungsmed. 2014;39(03):e72-e98. doi:10.1055/s-0034-1370084
Forbes A, Escher J, Hébuterne X, et al. ESPEN guideline: Clinical nutrition in inflammatory bowel disease. Clin Nutr. 2017;36(2):321-347. doi:10.1016/j.clnu.2016.12.027
Wolf E. Künstliche Ernährung: Wenn Essen keine Selbstverständlichkeit mehr ist. Pharmazeutische Zeitung. 1998;31. https://www.pharmazeutische-zeitung.de/inhalt-31-1998/titel-31-1998/. Accessed May 12, 2019.
Lünen VV (2011). Trinknahrungen: Aus dem All ans Krankenbett. Pharmazeutische Zeitung. 2011;03. https://www.pharmazeutische-zeitung.de/ausgabe-032011/trinknahrungen-aus-dem-all-ans-krankenbett/. Accessed May 16, 2019.
Hansen T, Duerksen DR. Enteral Nutrition in the Management of Pediatric and Adult Crohn's Disease. Nutrients. 2018;10(5):537. Published 2018 Apr 26. doi:10.3390/nu10050537
Stroud M, Duncan H, Nightingale J; British Society of Gastroenterology. Guidelines for enteral feeding in adult hospital patients. Gut. 2003;52 Suppl 7(Suppl 7):vii1–vii12. doi:10.1136/gut.52.suppl_7.vii1