Diet formulation and choice of enteral diet.

Once it has been decided to provide nutritional support via the enteral route the best formulation to meet the nutritional needs of the individual patient must be selected. A large number of enteral diets are now commercially available, and Table 1 summarises the different categories available. Until recently, controversy existed as to whether enteral feeds formulated and prepared in the hospital dietetic department should be used instead of their commercially prepared counterparts: problems caused by infection have now been well documented with "home brew" diets,' and there are now controlled data which show that the incidence of diarrhoea is higher when "home brew" rather than commercial diets are used for enteral feeding.2 Knowledge gained about the processes entailed in the physiology of nutritional absorption and subsequent metabolism both in normal and disease states continues to influence the formulation of enteral diets, and this review will outline recent advances in those areas that are influencing diet formulation. Fat absorption Over the past two years there have been few research findings that have actually influenced diet formulation. The importance of preventing essential fatty acid deficiency needs emphasising, particularly as it may occur when gut function is particularly impaired and long chain triglycerides are poorly assimilated.3 As previously outlined,4 medium chain triglycerides are probably not as well assimilated in the presence of bile salt deficiency, exocrine pancreatic insufficiency, and intestinal resection as many would believe, 5 and at least in the cases of exocrine pancreatic insufficiency and intestinal re-section pancreatic supplements will greatly enhance energy assimilation from medium chain triglycerides and reduce steatorrhoea.' Carbohydrate The physiology of digestion and absorption of Corrcspondtcncc to: Dr D B A Silk. Dcpi)rtmcnt ot (Gistrocnitcrologv dund Nutrition Ccntral Middlicscx tlospit.l. Acton Li.ne. Iondon NWI() 7NS. [ilgland. dietary carbohydrate in relation to formulation of enteral diets has been reviewed.7 Although the early chemically defined "elemental" diets administered to man contained glucose as the sole source of carbohydrate energy,8 9 the glucose content was soon replaced in part by sucrose,") and later by glucose polymer mixtures derived from the hydroly-sis of starch by a-amylase.7 Although the potential carbohydrate forms used in enteral diets have been categorised," Jones et al'2 characterised in detail the composition of starch hydrolysates commonly used as the carbohydrate energy source of enteral diets. Using gel permeation chromatography, they found that most consist of a very heterogenous mixture of glucose polymers with about 50% of the …