If Fat is Good, Is Muscle Better?
Kam Kalantar-Zadeh, MD, MPH, PhD
One of recent challenges in nephrology and other internal medicine subspecialties is providing care to an increasing number of patients with chronic disease states and wasting syndrome.
Patients with advanced CKD or congestive heart failure (CHF) frequently suffer from protein-energy wasting. In CKD patients, this condition has been usually referred to as uremic malnutrition. A low serum albumin level (below 3.8 g/dL) is the hallmark of protein-energy wasting in dialysis patients, but hypoalbuminemia can also be associated with chronic inflammation, as suggested by a high serum C-reactive protein (above 5 mg/L).
Such hypoalbuminemic or chronically inflamed patients usually have diminished fat and muscle mass and a high risk of death. A similar condition in CHF patients is known as cardiac cachexia.
Recent studies indicate that obese dialysis patients have greater survival. Does this mean that larger body fat protects against uremic malnutrition and its associated high mortality? Some researchers believe that larger BMI, which is often interpreted as obesity, may also be the result of having higher muscle mass.
Is this muscle or fat that confers greater survival to dialysis patients with higher BMI? Evidence indicates that low measures of the surrogates of both fat mass and lean body mass are associated with increased mortality in dialysis patients.
Nevertheless, it may sound counterintuitive to maintain that fat is associated with better survival, especially since obesity is a component of the metabolic syndrome and a known risk factor for diabetes and cardiovascular disease in otherwise healthy individuals. The preponderance of data showing a positive association between obesity and better survival in CKD patents is undeniable.
As a potential ground for reconciliation and collaboration between the muscle-centric and fat-favorable camps, an opinion leader recently suggested, “If fat is good, muscle is better.”
In this issue, T. Alp Ikizler, MD, has contributed to a concise review about causes and consequences of muscle wasting—also known as sarcopenia—in CKD patients. Protein-rich supplements, appetite stimulants, exercise training, and anabolic steroids are among the suggested interventions to correct uremic malnutrition and sarcopenia in dialysis patients as well as millions of other individuals with chronic disease and wasting disorder.
Kamyar Kalantar-Zadeh, MD, MPH, PhD, is Associate Professor of Medicine and Pediatrics, and Director, Dialysis Expansion & Epidemiology, Harbor-UCLA Division of Nephrology & Hypertension. He is the Medical Director for Nephrology at Renal & Urology News.