Elemental diets (EDs) have been used for over 50 years to manage various diseases, leveraging several mechanisms to produce beneficial effects. Despite their potential, they are underutilized because of palatability issues, access barriers, cost, and a general lack of awareness regarding their clinical efficacy. This article aims to systematically review the literature, summarizing the variability in ED formulations, their mechanisms of action, clinical applications, and tolerability in treating gastrointestinal (GI) diseases.
Introduction to Elemental Diets
An elemental diet is a liquid-only diet formulated to supply the body with essential nutrients in an easily digestible form. It is a special low-fat liquid formulation designed to be easily digested and contains all the essential nutrients necessary for a healthy diet. Unlike polymeric diets, which contain whole proteins, and oligomeric diets containing short peptides, EDs typically consist of free amino acids as their nitrogen source. The lipid content mainly comprises medium-chain triglycerides, which passively diffuse into the portal system, sometimes with added long-chain triglycerides. The carbohydrate component usually consists of monosaccharides (dextrose, glucose, or maltose) or easily digestible saccharide polymers like maltodextrins.
These diets are devoid of allergens and can be absorbed largely without active digestion, allowing for rapid nutrient absorption and high nutritional efficacy. This makes them effective for several GI and systemic diseases, particularly those driven by atopy, indigestion, and malabsorption. EDs also possess anti-inflammatory and mucosal healing properties, further contributing to their utility in inflammatory conditions. Given their high absorbability index, EDs generate little fecal bulk, providing additional benefit in cases of severe diarrhea, high output ostomies, and gastrointestinal fistulae.
Mechanisms of Action
Several mechanistic pathways mediate the effects of elemental diets, including their food additive and allergen-free content, high passive absorption rate, and anti-inflammatory properties. The diets likely work by reducing inflammation, balancing the gut microbiome, healing the gut lining, and providing complete nutrition without additives and allergens that typically irritate the gut.
Clinical Applications in Gastrointestinal Diseases
While large prospective trials are lacking, elemental diets appear to exhibit objective and subjective clinical benefits in several diseases.
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Eosinophilic Esophagitis (EoE)
EDs have been used in managing EoE in pediatric patients since the disease was described. Studies in pediatric cohorts have shown high response rates, ranging from 75% to 95%. In one study, all subjects showed symptomatic response (80% resolution and 20% improvement of symptoms) along with endoscopic and histologic improvement.
Two prospective studies have investigated the efficacy of exclusive ED in adult EoE. Peterson et al. assessed the efficacy of 4 weeks of ED on 29 adult patients with EoE. Compliance was poor, as 11 subjects (38%) could not tolerate the elemental diet. Of the remaining 18 subjects, one had a complete response at 2 weeks, and the rest completed 4 weeks of ED. Overall, there was a fivefold decrease in tissue eosinophil count. Of 18 subjects, 9 (50%) had a complete histologic response. Warners et al. prospectively assessed 34 adults with EoE. Only 17 subjects were able to finish 4 weeks of ED therapy (50% drop-out rate), mostly due to unpalatability. Of 17 patients, 16 (94%) showed complete or partial histologic response. Significant endoscopic improvement was observed, and fifteen patients (88%) became completely asymptomatic.
In the clinical guidelines by the American Gastroenterological Association and the Joint Task Force on Allergy-Immunology Practice Parameters, ED was described to have the highest response rate across treatment interventions, receiving a conditional recommendation for use in EoE.
Eosinophilic Gastritis and Gastroenteritis (EGID)
Gonsalves et al. assessed the efficacy of ED in 15 cases of eosinophilic gastritis and gastroenteritis in a prospective, single-arm trial. All 15 subjects had complete histologic remission in both the stomach and duodenum after 6 weeks of ED. Average eosinophil count dropped significantly in both the stomach and duodenum. Furthermore, all patients had improvements in molecular disease activity, endoscopic signs, and symptoms, including pain and fatigue.
Inflammatory Bowel Diseases (IBD)
Exclusive enteral nutrition (EEN) with liquid elemental, semi-elemental, or polymeric formulas for 6-8 weeks has been shown to be effective in Crohn’s disease (CD). In children and adolescents, EEN is recommended as first-line therapy for induction of remission. A 3 to 6 weeks of ED appear to be effective in inducing clinical, endoscopic, and histologic remission in CD.
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The role of ED in managing ulcerative colitis (UC) remains to be elucidated, with only one small study showing significant clinical improvement in both ED and blended normal diet groups. ED appears to be highly effective in inducing remission in adult and pediatric CD.
Small Intestinal Bacterial Overgrowth (SIBO) and Intestinal Methanogen Overgrowth (IMO)
While antibiotics are the mainstay of treatment for small intestinal bacterial overgrowth (SIBO) and intestinal methanogen overgrowth (IMO), their overall efficacy is limited. Elemental diet provides an alternative option to treat patients who are refractory, cannot tolerate antibiotics, or prefer a non-antibiotic treatment approach.
Pimentel et al. conducted a retrospective study on patients with irritable bowel syndrome (IBS) and hydrogen-predominant SIBO. Normalization of breath test was observed in 80% after 14 days and another 5% normalized with an extension to 21 days. Significant clinical improvement in symptoms (66%) was noticed among 28 patients who normalized their breath and had clinical data available. Rezaie et al. evaluated an oral palatable ED in a prospective clinical trial on 30 subjects with IMO and/or SIBO. All patients were able to tolerate 14 days of exclusive ED, and a significant drop in maximum methane levels and peak hydrogen rise were observed. Complete normalization of breath test was seen in 100%, 58%, and 75% in SIBO, IMO, and IMO/SIBO, respectively.
Celiac Disease and Dermatitis Herpetiformis
Kadunce et al. conducted a trial on 8 adult patients with dermatitis herpetiformis on dapsone, with most patients receiving an exclusive ED plus 30 g of gluten for 2 weeks followed by the ED alone for 2 weeks, while 2 subjects were given the dietary intervention in reverse order. Following the 2-week ED plus gluten phase, 100% of patients demonstrated histologic worsening of their celiac disease, and after only 2 weeks on the exclusive ED period, 100% demonstrated histologic improvement.
Tolerability and Limitations
High rates of intolerance, up to 40%, are seen in trials where exclusive elemental diets were administered orally due to poor organoleptic acceptability. However, when tolerated, adverse events were rare. Other limitations of elemental diets are cost, access, and lifestyle/social restrictions. Moreover, judicious use is advised in the presence of concomitant restrictive food intake disorders.
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Practical Guidelines for Implementing an Elemental Diet
What to Do Before Starting
Consult with a qualified healthcare provider regarding symptoms and what you might hope to gain from the diet. Based on the condition, the healthcare provider might recommend the diet for three to five days to manage acute symptoms, or for several weeks to give the digestive system a restorative rest and reboot. They will also provide instructions on how much of the formula to take to meet the body’s caloric needs.
What You Can and Cannot Consume
On the full elemental diet, you don’t eat any other foods. The point of the diet is to replace food and minimize digestive activity. Following the diet exactly allows your gut the rest it needs to heal. You may be allowed to drink tea without anything added. Sometimes healthcare providers recommend a “half-elemental diet” for people who need a secondary source of nutrition or who are transitioning into or out of the full diet. In this case, the elemental formulas provide half of your calories, and the other half come from food.
How to Survive the Elemental Diet
This diet is very restrictive, and it can be challenging. To stick to the diet successfully, healthcare providers recommend that you:
- Keep it cold: Blending the formula with ice, smoothie-style, makes it more palatable.
- Sip it slowly: Sip it slowly to prevent nausea and drink plenty of water between “meals."
- Make it portable: Have a temperature-controlled thermos to keep your formula in so you don’t get hungry when you’re out and about.
- Stay busy: Distract yourself with fun, non-food-related activities and good company.
Possible Side Effects
During the diet, you may experience symptoms that make you wonder if it’s actually helping your condition or making it worse. Medical guidance can help you sort through this. Symptoms may include:
- Abdominal cramping
- Detox symptoms
- Bacteria die-off symptoms
- Reduced motility
What to Do After the Elemental Diet
It’s important to reintroduce foods gradually as your digestive system is ramping back up again. Healthcare providers typically recommend following a half-elemental diet or a low-FODMAP diet during the transition. They may also recommend probiotics to re-populate your gut with beneficial flora and prokinetic agents to stimulate your bowels to begin moving more regularly again. As you return to your more regular diet, pay attention to the way different foods affect your digestive system.
Practitioner's Guide to Implementing the Elemental Diet
Implementing the elemental diet in clinical practice involves several key steps to ensure patient safety, compliance, and effectiveness:
- Patient Assessment: Determine if the ED is appropriate for the patient and screen for any contraindications, including diabetes, fungal overgrowth, or a history of eating disorders.
- Patient Preparation and Education: Educate the patient on the purpose and process of the elemental diet, explaining the mental and emotional challenges and the unpalatable taste.
- Diet Selection: Recommend a prescription or nonprescription commercial ED formula or provide recipes for patients to make their formula at home. Calculate the patient's daily caloric needs based on their age, weight, activity level, and clinical condition.
- Monitoring and Support: Healthcare providers should be readily available to their patients during the ED protocol to monitor their clinical response, including symptom improvement and side effects, and address any questions that arise.
- Assess Treatment Efficacy: Once the ED is completed, SIBO status can be evaluated by repeating the SIBO breath test or assessing the patient's clinical symptoms.
Transitioning Off the Elemental Diet
Once the patient has completed their protocol, they should be guided in gradually reintroducing solid foods back into their diet to prevent digestive upset. An alternative approach would be to follow a half-elemental diet or incorporate dietary strategies into a long-term prevention plan, such as the Low-FODMAP Diet, Specific Carbohydrate Diet (SCD), or SIBO Bi-Phasic Diet (SIBO B-PD).
Tips for Maximizing Success
Here are tips that can help your patients successfully follow an elemental diet:
- Take the time to properly prepare your patients before they start the ED.
- Modify the ED by prescribing a semi-elemental diet or a shortened ED protocol.
- Prevent fungal overgrowth by prescribing prophylactic antifungals.
- Make the ED more palatable by recommending a flavored commercial ED or semi-elemental formula or drinking the beverage cold.
- Make the ED more affordable by having patients make their ED formula at home instead of buying commercial products.
- Regulate blood sugar by instructing patients to sip on their elemental shake throughout the day instead of drinking three "meals."
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