Patients not ready for a regular diet due to elective or emergent procedures, or who experience irregularity in gastrointestinal function, dysphagia, a transition from prolonged fasted periods, etc. are typically placed on a restrictive diet. Dietary restrictions can be as restrictive as no food or liquids allowed by mouth, which may increase in a stepwise fashion until reaching regular nutrition. One step in that progression is a full liquid diet. A patient prescribed a full liquid diet follows a specific diet type requiring the intake of all liquids and semi-liquids, but no forms of solid intake. Unlike a clear liquid diet, which includes only liquids and semi-liquids that are non-opaque, a full liquid diet is more inclusive, as it allows all types of liquids.
The use of any modified diet, including a full liquid diet, can be a potential issue for patients if used long term. In patients with oropharyngeal dysphagia, for example, this type of modified diet can lead to poor nutrition. The use of modified diets, including full thickened liquid diets in long term care patients, has correlations with higher BUN and creatinine levels as well as higher rates of dehydration over time. The use of certain types of full liquid diets can also affect drug absorption. Studies have shown that the use of full thickened liquid diets to take medications can affect the rate of absorption by delaying drug dissolution. Finally, full liquid diets can affect a patient's quality of life over time due to patient dissatisfaction with taste when supplemented with nutrients, patient discomfort with the texture of diet lacking solid food, and increased thirst depending on what full liquids the patient receives.
Even with the concerns associated with modified diets due to poor nutrition, full liquid diets have historically been more likely than clear liquid diets to be supplemented with commercial formulas that provide a higher caloric intake for patients. This difference can be as drastic as a less than 1000 kilocalorie daily intake in patients on clear liquid diets that are not supplemented with commercial formulas to greater than 15000 kilocalories intake for patients on a full liquid diet supplemented with commercial formulas. This state is clinically significant due to the potential of a full liquid diet to be more efficacious in patients on dietary restriction who require a higher caloric intake. Full liquid diets are also potentially beneficial for patients suffering from dysphagia, as the texture and consistency provide less risk of penetration-aspiration; however, more research is necessary to fully understand the role of full liquid diets relative to swallowing physiology.
The main indication for a full liquid diet is in the perioperative period. This refers to the period around the time of the operation, including pre- and post-operative management. Other more restrictive diets can be used during this time as well. Still, one added benefit of a full liquid diet is the higher amount of calories and added amount of nutrients provided, which has links to fewer post-operative complications. This situation especially becomes an issue of importance for patients receiving surgery on any part of the gastrointestinal tract, who is in any way immunosuppressed, such as a cancer patient. Bozzetti et al. showed that the most significant postoperative complications in patients with gastric cancer included weight loss, advanced age, earlier surgery involving the pancreas, and lower serum albumin. Increasing amounts of nutritional support reduced postoperative complications. The best form of nutritional support for those patients was immune-enhanced, but results showed an increased protective effect against complications with an increase in nutritional support. Although more research is needed to confirm the implication, this and other studies imply the added benefit of a full liquid diet when compared to its more restrictive counterparts in preventing malnutrition in even non-immunosuppressed patients. In abdominal surgeries for patients regardless of their immunosuppressive state, the typical dietary progression post-operatively is one that begins with a clear liquid diet while recovering from anesthesia, followed by the full liquid diet, then a soft diet, and finally regular dietary intake.
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