Title: The efficacy of elemental and polymeric diets in the treatment of Crohn’s disease
Key words: enteral nutrition, parenteral nutrition, steroid therapy Crohn’s disease, remission, relapse, steroid dependency, amino acids, elemental, polymeric, nitrogen content, protein, fat content, triglycerides, medium chain fatty acids, polyunsaturates, eicosanoids, palatability, fat-soluble antioxidants, efficacy,
Date: Sept 2006
Category: Special diets, Specific conditions
Author: Morgan, G
The efficacy of elemental and polymeric diets in the treatment of Crohn’s disease
Enteral nutrition has been employed in the treatment of active Crohn’s disease since the 1970’s when studies showed it to be as effective as steroid therapy in promoting remission (O’Morain 1984). Both total parenteral nutrition, enteral nutrition and the combination of enteral nutrition plus food led to similar remission rates (Greenberg 1988). It was thought that relative ‘bowel rest’ combined with improved nutrition accounted for the positive results (Lochs 1983, Greenberg 1988), an effect reflected in the lower clinical indices of Crohn’s activity in trials (O’Morain 1980, Lochs 1991).
The results were much higher than could be accounted for by the placebo effect of 20-30% remission rates after 6-8 weeks (Summers 1979). Subsequent meta-analyses of the data have shown enteral nutrition to be inferior to steroid therapy in promoting remission in Crohn’s disease (Griffiths 1995, Fernandez-Banares 1995). Given the high relapse rates following steroid therapy – up to 80% in the 12 month period following acute treatment in one study (Malchow 1984) – and the unwelcome side effects of steroid dependency, serious consideration has been given to enteral nutrition as a management tool for mild to moderate Crohn’s disease. This paper comments on the results and the place of enteral nutrition.
Liquid enteral nutrition is administered in either elemental or polymeric form. The efficacy of such diets is thought to reside in their nitrogen content, in the form of amino acids in the case of the elemental diet, and protein homogenates in the case of the polymeric diet. Four controlled trials have been carried out comparing the efficacy of elemental and polymeric diets in promoting and prolonging remissions in active Crohn’s disease (Giaffer 1990, Rigaud 1991, Park 1991, Raouf 1991). Meta-analysis of these data showed no statistical difference in their relative efficacies - 64.7% versus 61.7% respectively (Fernandez-Banares 1995). One further study showed an improved response to the elemental diet but this was not significant (Verma 2000).
Subsequent analysis looking at corporate data from controlled and uncontrolled series has shown corresponding rates of 79% and 70%, indicating greater efficacy for the elemental diet (Gassull 2001). However these figures also fail to account for the variation in study design, the composition of the enteral feeds and the underpowered nature of the majority of the studies (O’Sullivan 2001). It now seems likely that both elemental and polymeric diets are effective in the treatment of acute and relapsing Crohn’s disease (Teahon 1990, Verma 2001). More recent work on the fat composition of enteral feeds has helped to clarify the role of non-nitrogenous components present in such feeds and goes some way to explaining the great variance of many of the studies. The fat content of enteral feeds varies enormously, from 1.4 to 40G/kcal (Fernandez-Banares 1995).
For polymeric formulae such as Triosorbon, Enteral 400, and Ensure significantly different response rates have been found (Fernandez-Banares 1995). A higher content of long-chain triglycerides has been reported to reduce and a higher content of medium-chain fatty acids to increase efficacy ((Middleton 1995, Bamba 2003). The degree of fatty acid desaturation also appears to be a factor, an effect that could be mediated by the anti-inflammatory effects of eicosanoids associated with specific polyunsaturates (Geerling 1999, Fell 2000, James 2000, Gassull 2002).
Polymeric diets contain relatively large amounts of fat (Gorard 2003). This may improve the palatability and reduce the dropout rate for patients on this type of enteral feed but, depending on the fatty acid profile of the formula and fat-related factors such as its content of fat-soluble antioxidants (Geerling 1999), the overall efficacy of the formula may be significantly jeopardised.
In summary, at present there appears insufficient evidence to support the idea that elemental diets are superior to polymeric diets in the management of Crohn’s disease. This view derives from the poor methodology and low power of the studies conducted in this field. The view that the undoubted efficacy of enteral diets is due to their content must now be challenged in the light of the above fat composition studies. Fatty acid composition and the precise role played by the antioxidant and anti-inflammatory properties of polymeric diets have yet to be determined. Larger, more closely controlled studies are called for to clarify these issues. Interaction between such factors at present renders it impossible to ascertain the relative merits of an amino- acid over a whole protein based formula. The formulation of such an ideal enteric feed thus poses a challenge both for primary research within the field of Crohn’s disease and for the pharmaceutical industry in its efforts to produce more acceptable and effective feeds.
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