Clear Liquid Diet

Anatomy and Physiology

The digestive system begins at the mouth. Saliva is released in response to autonomic stimulation from olfactory and gustatory input, as well as mastication, and facilitates several functions, including swallowing. Swallowing clear liquids occurs by voluntarily moving the liquid to the back of the mouth but requiring less oral mechanical coordination from the tongue and cheeks when compared to swallowing solids. The soft palate closes reflexively to separate the oropharynx from the nasopharynx, and the larynx elevates with simultaneous coverage of the laryngeal inlet by the epiglottis, protecting the lower airway.

The upper esophageal sphincter relaxes to allow entry of the bolus, and involuntary peristalsis moves the liquid down the esophagus with coordinated, wave-like contractions into the stomach. In the stomach, digestive enzymes break down proteins into amino acids, fats into fatty acids and glycerol, and carbohydrates into simple sugars. This process is stimulated by the presence of proteins, fats, and carbohydrates in the stomach. Clear liquids are the easiest for the body to break down because they have very few proteins and fats and are predominantly made up of easily digestible carbohydrates, causing less gastric stimulation. This digestive mix is called chyme, and it moves into the small intestine, where the walls of the small intestine (via lumenal projections called villi) absorb nutrients and water. Next, it progresses to the large intestine, which absorbs water and condenses the chyme into a stool, and then moves to the rectum, where it is excreted through the anus.  

Indications

Indications for a clear liquid diet include a number of medical conditions or surgical procedures.

Examples include[2]:

• Prior to procedures to minimize gastric stimulation and contents
• Post-operatively to minimize gastric stimulation and nausea
• Diverticulitis to decrease stool in the colon
• Nausea, vomiting, diarrhea

Contraindications

While there are no formal contraindications for a clear liquid diet, there are some significant considerations when utilizing this diet choice.

Many foods available to this diet are high in carbohydrates and simple sugars, and patients with diabetes mellitus are at increased risk for hyper- and hypoglycemia. Blood glucose should be monitored frequently and any insulin doses adjusted.

Most common clear liquids are thin liquids, and some patients may be at risk of aspiration. The majority of these liquids can be thickened easily and effectively, though the choice of thickener is also important as some are starch-based. The input of a speech and language pathologist is very helpful.

It can be challenging to provide the necessary nutrients and calories needed while maintaining a clear liquid diet, so the transition to solid foods should take place as rapidly as possible and interprofessional communication can produce the best patient outcomes.[3]

Personnel

If the patient is in an in-patient facility, the nurse will review the diet order. All healthcare team members need to have a complete understanding regarding what items are acceptable in a clear liquid diet. This should be reviewed in detail with the patient as well. In addition, conversations with the interprofessional team should occur as needed about the patient's readiness to advance the diet. 

If a person will be utilizing a clear liquid diet at home, it is important to ensure proper patient education when ordering such a diet, as it can be both challenging and frustrating for patients.

Technique or Treatment

It is recommended to minimize gastric volume and stimulation in the immediate preoperative period to lower the risk of aspiration with general anesthesia. Different food items are digested and emptied from the stomach at different rates and stimulate gastric secretions and acid production depending upon their constituent makeup. To mitigate this risk, most providers recommend not to eat solid foods eight hours prior to the procedure and may allow clear liquids up to two hours before procedures.[4]

A clear liquid diet is typically ordered before gastrointestinal procedures, such as endoscopies or colonoscopies, in addition to the bowel preparation regimen prescribed. It is critical to adhere to this process before the procedure so the provider can clearly visualize the gastrointestinal tract. Some physicians also recommend avoiding red and orange-colored items in such pre-procedural settings, as the color residue may appear blood-like during the procedure and potentially cause confusion.[5][6]

After a procedure that utilizes sedation or general anesthesia, a clear liquid diet may be ordered as part of the recovery process. Using a relatively non-stimulating clear liquid diet can decrease the risk of nausea before progressing to more substantial foods. Beginning with a few ice chips, a postoperative patient's ability to control their swallow reflex can be assessed. If they do not cough or clear their throat after the ice chips, they are likely ready to try a sip of water. Assessing the patient’s swallowing ability with the first sip. If they do not demonstrate any difficulty, they are likely ready to advance to other clear liquids as ordered. If the patient is drowsy, coughs, clears their throat, or cannot swallow, they may need additional time to recover from the anesthesia to try again, or they may need further follow-up with speech therapy for a formal swallow study if this is prolonged. If the patient cannot keep their airway clear or handle their own oral secretions, do not continue diet without notifying the physician. Wait for 1 to 2 hours after the throat has been numbed for any otolaryngic or bronchoscopic procedure.[7]

A clear liquid diet is used in treating uncomplicated diverticulitis, nausea, vomiting, diarrhea, or other gastrointestinal maladies. Utilizing a clear liquid diet for these instances allows for bowel rest and healing, avoiding potentially aggravating foods but still allowing clear liquids helps maintain hydration, electrolytes, and satiety while limiting the strain of digestion.[8]

Enhancing Healthcare Team Outcomes

Always utilize the facility policy for specific instructions. It is essential to be aware of what constitutes a clear liquid item and what is not. Providing clear communication with the healthcare team is vital, especially with special circumstances such as patients with diabetes or dysphagia. This will include the clinicians (including mid-level practitioners), dieticians, nurses, and in some cases, pharmacists. Patient education should include not only what is the clear liquid diet but also why they are on this diet. Keep in mind the transition to solid foods and reassess readiness regularly.[9][7][10]