The recent research findings concerning syndromes of muscle wasting, malnutrition, and inflammation in individuals with chronic kidney disease (CKD) or acute kidney injury (AKI) have led to a need for new terminology. To address this need, the International Society of Renal Nutrition and Metabolism (ISRNM) convened an expert panel to review and develop standard terminologies and definitions related to wasting, cachexia, malnutrition, and inflammation in CKD and AKI. The ISRNM expert panel recommends the term 'protein-energy wasting' for loss of body protein mass and fuel reserves. 'Kidney disease wasting' refers to the occurrence of protein-energy wasting in CKD or AKI regardless of the cause. Cachexia is a severe form of protein-energy wasting that occurs infrequently in kidney disease. Protein-energy wasting is diagnosed if three characteristics are present (low serum levels of albumin, transthyretin, or cholesterol), reduced body mass (low or reduced body or fat mass or weight loss with reduced intake of protein and energy), and reduced muscle mass (muscle wasting or sarcopenia, reduced mid-arm muscle circumference). The kidney disease wasting is divided into two main categories of CKD- and AKI-associated protein-energy wasting. Measures of chronic inflammation or other developing tests can be useful clues for the existence of protein-energy wasting but do not define protein-energy wasting. Clinical staging and potential treatment strategies for protein-energy wasting are to be developed in the future.

Protein energy wasting (PEW) is common in patients with chronic kidney disease (CKD) and is associated with adverse clinical outcomes, especially in individuals receiving maintenance dialysis therapy. A multitude of factors can affect the nutritional and metabolic status of CKD patients requiring a combination of therapeutic maneuvers to prevent or reverse protein and energy depletion. These include optimizing dietary nutrient intake, appropriate treatment of metabolic disturbances such as metabolic acidosis, systemic inflammation, and hormonal deficiencies, and prescribing optimized dialytic regimens. In patients where oral dietary intake from regular meals cannot maintain adequate nutritional status, nutritional supplementation, administered orally, enterally, or parenterally, is shown to be effective in replenishing protein and energy stores. In clinical practice, the advantages of oral nutritional supplements include proven efficacy, safety, and compliance. Anabolic strategies such as anabolic steroids, growth hormone, and exercise, in combination with nutritional supplementation or alone, have been shown to improve protein stores and represent potential additional approaches for the treatment of PEW. Appetite stimulants, anti-inflammatory interventions, and newer anabolic agents are emerging as novel therapies. While numerous epidemiological data suggest that an improvement in biomarkers of nutritional status is associated with improved survival, there are no large randomized clinical trials that have tested the effectiveness of nutritional interventions on mortality and morbidity.

Enteral nutrition (EN) by means of oral nutritional supplements (ONS) and tube feeding (TF) offers the possibility of increasing or ensuring nutrient intake in cases where normal food intake is inadequate. These guidelines are intended to give evidence-based recommendations for the use of ONS and TF in nephrology patients. They were developed by an interdisciplinary expert group in accordance with officially accepted standards and are based on all relevant publications since 1985. They were discussed and accepted in a consensus conference. Because of the nutritional impact of renal diseases, EN is widely used in nephrology practice. Patients with acute renal failure (ARF) and critical illness are characterized by a highly catabolic state and need depurative techniques inducing massive nutrient loss. EN by TF is the preferred route for nutritional support in these patients. EN by means of ONS is the preferred way of refeeding for depleted conservatively treated chronic renal failure patients and dialysis patients. Undernutrition is an independent factor of survival in dialysis patients. ONS was shown to improve nutritional status in this setting. An increase in survival has been recently reported when nutritional status was improved by ONS.

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Although intradialytic parenteral nutrition (IDPN) is a method used widely to combat protein-calorie malnutrition in hemodialysis patients, its effect on survival has not been thoroughly studied. We conducted a prospective, randomized trial in which 186 malnourished hemodialysis patients received oral nutritional supplements with or without 1 year of IDPN. IDPN did not improve 2-year mortality (primary end point), hospitalization rate, Karnofsky score, body mass index, or laboratory markers of nutritional status. Instead, both groups demonstrated improvement in body mass index and the nutritional parameters serum albumin and prealbumin (P Ͻ 0.05). Multivariate analysis showed that an increase in prealbumin of Ͼ30 mg/L within 3 months, a marker of nutritional improvement, independently predicted a 54% decrease in 2-year mortality, as well as reduced hospitalizations and improved general well-being as measured by the Karnofsky score. Therefore, although we found no definite advantage of adding IDPN to oral nutritional supplementation, this is the first prospective study demonstrating that an improvement in prealbumin during nutritional therapy is associated with a decrease in morbidity and mortality in malnourished hemodialysis patients.

There has been renewed interest in vitamin D since numerous recent studies have suggested that besides its well-established roles in bone metabolism and immunity, vitamin D status is inversely associated with the incidence of several diseases, e.g., cancers, cardio-vascular diseases, and neurodegenerative diseases. Surprisingly, there is very little data on factors that affect absorption of this fat-soluble vitamin, although it is acknowledged that dietary vitamin D could help to fight against the subdeficient vitamin D status that is common in several populations. This review describes the state of the art concerning the fate of vitamin D in the human upper gastrointestinal tract and on the factors assumed to affect its absorption efficiency. The main conclusions are: (i) ergocalciferol (vitamin D2), the form mostly used in supplements and fortified foods, is apparently absorbed with similar efficiency to cholecalciferol (vitamin D3, the main dietary form), (ii) 25-hydroxyvitamin D (25OHD), the metabolite produced in the liver, and which can be found in foods, is better absorbed than the nonhydroxy vitamin D forms cholecalciferol and ergocalciferol, (iii) the amount of fat with which vitamin D is ingested does not seem to significantly modify the bioavailability of vitamin D3, (iv) the food matrix has apparently little effect on vitamin D bioavailability, (v) sucrose polyesters (Olestra) and tetrahydrolipstatin (orlistat) probably diminish vitamin D absorption, and (vi) there is apparently no effect of aging on vitamin D absorption efficiency. We also find that there is insufficient, or even no data on the following factors suspected of affecting vitamin D bioavailability: (i) effect of type and amount of dietary fiber, (ii) effect of vitamin D status, and (iii) effect of genetic variation in proteins involved in its intestinal absorption. In conclusion, further studies are needed to improve our knowledge of factors affecting vitamin D absorption efficiency. Clinical studies with labeled vitamin D, e.g., deuterated or (13)C, are needed to accurately and definitively assess the effect of various factors on its bioavailability.

Protein-energy wasting (PEW), which is manifested by low serum levels of albumin or prealbumin, sarcopenia and weight loss, is one of the strongest predictors of mortality in patients with chronic kidney disease (CKD). Although PEW might be engendered by non-nutritional conditions, such as inflammation or other comorbidities, the question of causality does not refute the effectiveness of dietary interventions and nutritional support in improving outcomes in patients with CKD. The literature indicates that PEW can be mitigated or corrected with an appropriate diet and enteral nutritional support that targets dietary protein intake. In-center meals or oral supplements provided during dialysis therapy are feasible and inexpensive interventions that might improve survival and quality of life in patients with CKD. Dietary requirements and enteral nutritional support must also be considered in patients with CKD and diabetes mellitus, in patients undergoing peritoneal dialysis, renal transplant recipients, and in children with CKD. Adjunctive pharmacological therapies, such as appetite stimulants, anabolic hormones, and antioxidative or anti-inflammatory agents, might augment dietary interventions. Intraperitoneal or intradialytic parenteral nutrition should be considered for patients with PEW whenever enteral interventions are not possible or are ineffective. Controlled trials are needed to better assess the effectiveness of in-center meals and oral supplements.

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