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Reply to A Sandek et al

Division of Nephrology and Hypertension
Los Angeles Biomedical Institute at Harbor–UCLA Medical
Center
Torrance, CA 90502

Denis Fouque

Division of Nephrology
Hospices Civils de LyonUniversity Claude Bernard
Lyon
France

Stefan D Anker

Division of Applied Cachexia Research
Department of Cardiology
University Hospital Charité
Campus Virchow-Klinikum
13353 Berlin
Germany

Dear Sir:

We thank Sandek et al for their important comments on our recent paper about the association of body fat and its changes over time with quality of life and prospective mortality in dialysis patients (1). In our study, we focused on all-cause mortality but agree that an examination of cause-specific mortality, including death from cardiovascular disease, may be clinically relevant as well, especially because almost one-half of all causes of death in dialysis patients are attributable to cardiovascular events (2). However, the diagnosis of death due to cardiovascular disease may be subject to ascertainment bias, especially if death certificates are used as the main source of determining the cause of death.

We also agree that the assessment of inflammation in dialysis patients is somewhat challenging, because most dialysis patients take many medications, including those with potential antiinflammatory properties, such as angiotensin-converting enzyme inhibitors or angiotensin-receptor blocker, ß blockers, and statins. Hence, the use of a precise medication record may better control for this important confounding, which we plan to pursue in our future studies.

Dual energy X-ray absorptiometry (DXA) is probably more accurate than is near-infrared (NIR) interactance in assessing body composition. However, DXA is a more elaborate method and cannot be readily implemented in large-scale epidemiologic studies with repeated measures. In such studies, NIR appears more practical and user-friendly. We recently found that the accuracy of NIR in the assessment of total percentage body fat in dialysis patients is comparable with DXA (3).

Undoubtedly, more studies are needed in several patient populations with cachexia and reverse epidemiology, including dialysis patients and patients with chronic heart failure (CHF). Both of these groups of patients show similar cardiovascular disease risk paradoxes (4). The growing body of literature pertaining to the reverse epidemiology of conventional cardiovascular disease risk factors, including the "obesity paradox," may have major clinical and public health implications, especially because the current practice of medicine is heavily based on the universal opinion that "losing fat is better in everybody" (5). Many overweight dialysis and CHF patients may not benefit from losing weight. On the contrary, weight loss may be associated with adverse outcomes (6). Clinical trials to increase weight, muscle mass, and even body fat in cachectic dialysis and CHF patients are urgently needed.

ACKNOWLEDGMENTS

No conflict of interest was declared by any of the coauthors.

REFERENCES

1. Kalantar-Zadeh K, Kuwae N, Wu DY, et al. Associations of body fat and its changes over time with quality of life and prospective mortality in hemodialysis patients. Am J Clin Nutr 2006;83:202–10.[Abstract/Free Full Text]
2. US Renal Data System. Excerpts from the United States Renal Data System 2005 annual data report: atlas of end-stage renal disease in the United States. Am J Kidney Dis 2006;47(suppl):1–286.[Medline]
3. Kalantar-Zadeh K, Bross R, Zitterkoph J, Colman S, Gjertson DW, Kopple JD. Comparing four body composition assessment methods for body fat measurement in dialysis patients. 37th annual conference of the American Society of Nephrology. J Am Soc Nephrol 2004;15(suppl):591A(abstr).
4. Kalantar-Zadeh K, Abbott KC, Kronenberg F, Anker SD, Horwich TB, Fonarow GC. Epidemiology of dialysis patients and heart failure patients; special review article for the 25th anniversary of the Seminars in Nephrology. Semin Nephrol 2006;26:118–33.[Medline]
5. Mobbs CV, Makimura H. Block the FAS, lose the fat. Nat Med 2002;8:335–6.[Medline]
6. Anker SD, Negassa A, Coats AJ, et al. Prognostic importance of weight loss in chronic heart failure and the effect of treatment with angiotensin-converting-enzyme inhibitors: an observational study. Lancet 2003;361:1077–83.[Medline]

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