Nutrition Program Nephrology Division Federal University of Sao Paulo Sao Paulo Brazil Email: lilian{at}dis.epm.br
Sir,
We appreciate the interest of Di Iorio and Bellizzi in our recently published paper, concerning the comparison of skinfold thickness and bioelectrical impedance analysis with dual-energy X-ray absorptiometry for the assessment of body fat in patients on long-term haemodialysis therapy.
Regarding their questions, Is it more important in haemodialysis patients to measure obesity or malnutrition? and Is it more relevant in haemodialysis patients to measure body fat or total body water?, to the best of our knowledge the measurement of body fat mass is part of the nutritional assessment and is an important parameter in evaluating both obesity and malnutrition. The fact that we conducted our comparative analysis of body fat compartment does not exclude the importance of assessing lean body mass and/or hydration status in this population. We cannot agree with Drs Di Iorio and Bellizzi, who consider body fat is not essential for haemodialysis patients, as fat carries out a potential role in covering the individuals energy requirements, especially in patients who are exposed to several catabolic conditions, as is the renal population. Moreover, a poor nutritional status can be identified by waste of total body mass, including fat content. In fact, Qureshi et al. [1] demonstrated in a cross-sectional study that a low skinfold thickness is one of the anthropometric factors associated with malnutrition in haemodialysis patients. Although studies have shown that chronic renal failure patients present reduced skinfold measurement in comparison with healthy individuals [2], its implication on long-term outcome of haemodialysis treatment is not well defined. However, lower values of BMI, which is a parameter related most directly to body fat mass, have been associated with high mortality in chronic renal patients [3].
Body composition of haemodialysis patients can suffer changes over time; however, few studies have analysed the modifications of total body fat in these patients. Prospective studies of body fat compartment using dual-energy X-ray absorptiometry have demonstrated a significant increase in fat mass in the first year of maintenance haemodialysis [4,5]. In male diabetic patients a decrease in body fat has been observed [6]. A very recent study including a large number of haemodialysis patients suggested a gradual increase of fat mass during the first 3 years and a decrease thereafter [7]. Although a possible benefit of excess body weight to the survival of dialysis patients has been demonstrated by some authors [3,8,9], the clinical importance of obesity in chronic renal failure patients and the real effect of excess weight on morbidity and mortality in this population remain to be elucidated. As well as lean body mass, the measurement of body fat is thus of interest to monitor renal failure patients, in an attempt to reduce their risk of death. And further, an individual follow-up of those body compartments changes is of much greater importance than a simple comparison with reference values, as we know there is a lack of standard references developed specifically to this population.
Our study compared the most simple methods of body composition analysis in clinical practice for the assessment of body fat in haemodialysis patients, and showed that the long established technique of skinfold thickness worked more similarly to the reference dual-energy X-ray absorptiometry than the bioelectrical impedance analysis, which tended to under-estimate fat measures in men and over-estimate them in women. Our data emphasized the importance of conducting a comparative body composition analysis stratified by gender. The predictive power of various nutritional markers has been shown to differ markedly between male and female in chronic renal failure patients [10].
Finally, the fat content provides valuable information for an adequate nutritional management of haemodialysis population and is an important nutritional parameter to monitor in the routine care of the renal population. The fact that bioelectrical impedance analysis results presented gender-specific variability for estimating adiposity in haemodialysis patients does not exclude the ability of this method to measure body water and predict hospitalization and mortality through its derived vectors.
Conflict of interest statement. None declared.
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