Malnutrition in CKD is common and is defined as inadequate intake of protein and/or energy over prolonged periods of time resulting in loss of fat and/or sarcopenia (loss of muscle stores) [11]. Malnutrition in patients with CKD is associated with increased morbidity and mortality; its etiology is multifactorial [5, 9, 12]. Malnutrition may ultimately lead to loss of vigor, poor rehabilitation and quality of life, and death [12]. Many non-dietary factors contribute to malnutrition in patients with CKD (Fig. 13.2).

While common lore is that patients with any form of CKD should reduce protein intake, studies consistently report inadequate oral intake, especially of protein, as a major contributing factor to malnutrition, including in patients with only a mild decline in GFR (i.e., <50 mL/min). Studies have further documented that dietary protein intake declines progressively with declining GFR [12, 13]. The reason for malnutrition from inadequate protein intake by patients with declining kidney function is not fully understood, but overzealous dietary restrictions are thought to contribute [4, 9–12]. Although general dietary recommendations for a “renal diet” are to limit protein, sodium, potassium, phosphorus, and fluids, general dietary recommendations should not be applied to individuals. Not all patients with CKD should limit their intake of the above, especially those with preexisting malnutrition and poor oral intake. Dietary intervention should be instituted only after each patient’s nutritional status and eating habits have been evaluated and there is a clear and demonstrated need for change [5]. This is the role of medical nutrition therapy as developed, prescribed, and implemented by a RDN. Specific dietary parameters for each stage of kidney disease are shown (Table 13.2).

Prior to the initiation of any diet restrictions or other modifications, patients with early CKD may not require specific nutrition therapy but, rather, may follow general healthy dietary guidelines, such as those promoted by the NKF KDOQI (Table 13.2) or the 2015 Dietary Guidelines for Americans (Appendix X). The 2010 version of these included, for the first time, recommendations targeting risk reduction for cardiovascular disease for the general population [14]. The guidelines included recommendations to decrease overweight and obesity and to include fruits, vegetables, whole grains, low-fat dairy, lean protein foods, and vegetable oils while limiting saturated fatty acids, trans-fatty acids, cholesterol, excess sugar, sodium, and refined grains. After the release of the 2015 guidelines [15], which were similar to those of 2010, many questioned whether they could or should be applied to patients with CKD [16]. The Dietary Approaches to Stop Hypertension (DASH) diet (Appendix X), a set of guidelines promoting a relatively rich intake of fruits, vegetables, calcium, and a lower sodium intake, has been proposed as a general diet capable of reducing progression of CKD [17, 18]. With the caveat that patients with CKD should be monitored for the presence of hyperkalemia and hyperphosphatemia, especially as the above dietary guidelines share a recommendation for a relatively high potassium intake (especially the DASH diet), there is general consensus that these guidelines are suitable for patients with CKD and that individual modifications should be made as needed, especially if/when patients progress to later stages.

Individualized medical nutrition therapy is designed and implemented by a RD after evaluating a patient’s medical history, renal function, and nutritional status. The following are key aspects of consideration in patients with CKD.