An assessment of the methods available to determine nutritional equilibrium in patients with chronic renal failure.

that on average 16% of protein is nitrogen). A major Assessment of status and nitrogen balance problem associated with this is that most patients are not in balance at any one time. To overcome this one The nutritional assessment of patients with chronic needs to undertake nitrogen balance whereby patients renal failure includes an assessment of body fat, fat are admitted to a metabolic ward and placed either on free mass (subdivided into somatic and visceral protein) a diet with the same caloric and nitrogen content as [1] and dietary intake. Figure 1 shows some of the their usual diet (isocaloric, isonitrogenous) or an methods that can be used to assess fat free mass and experimental diet if this the aim of the study [4,5]. All dietary intake. A few are applicable to everyday clinical urine and faeces are collected and the nitrogen content practice whereas others should be seen only as research (UN and N ) measured directly. The nitrogen intake tools. Methods of dietary assessment include precise N ) is calculated by the direct measurement of nitrogen weighing, a weighed inventory, a dietary history and in an aliquot from a homogenate of a parallel total dietary recall [2,3]. In clinical practice a 3 day dietary daily dietary intake. In CRF it is necessary to take history is commonly used but lacks the accuracy necesinto account any changes that may occur in the body sary for clinical research. Most such studies use a urea nitrogen pool (BUN×Vd ) during the period of weighed inventory. However, with increasing complexassessment with daily measurements of BUN. Using ity of dietary assessment there is a danger that patients linear regression the change in the pool N ) can then will change their normal dietary practice to facilitate be estimated and used to calculate nitrogen balance the assessment. Another method that is commonly (BN ) where: used is to measure the urea production rate and then using a variety of regression equations derived from BN=IN−UN−FN−DN other studies to estimate total nitrogen output. It is To undertake accurate nitrogen balance studies then assumed that the patient is in neutral nitrogen requires meticulous attention to detail [6 ]. It is not a balance (i.e. what is going in equals what is coming tool that can be used in routine clinical practice and out) and the dietary protein intake is therefore the there are now only a few clinical research centres world product of the total nitrogen output and 6.25 (assuming wide capable of undertaking it. If the aim of the study is to assess the effect of a dietary intervention it is necessary to allow a period of equilibration of up to one week before starting to measure nitrogen balance.