A specific protein-enriched enteral formula decreases cortisolemia and improves plasma albumin and amino acid concentrations in elderly patients

Abstract

Background
Old age is associated with an involuntary and progressive but physiological loss of muscle mass. The aim of this study was to evaluate the effects of exclusive consumption for 6 months of a protein-enriched enteral diet with a relatively high content of branched-chain amino acids on albuminemia, cortisolemia, plasma amino acids, insulin resistance, and inflammation biomarkers in elderly patients.

Methods
Thirty-two patients from the Clinical Nutrition Outpatient Unit at our hospital exclusively consumed a protein-enriched enteral diet for 6 months. Data were collected at baseline and at 3 and 6 months on anthropometric and biochemical parameters and on plasma concentrations of amino acids, cortisol, adrenocorticotropic hormone, urea, creatinine, insulin resistance, and inflammation biomarkers.

Results
The percentage of patients with albumin concentration below normal cut-off values decreased from 18% to 0% by the end of the study. At 6 months, concentrations of total plasma (p = 0.008) and essential amino acids (p = 0.011), especially branched-chain amino acids (p = 0.031), were higher versus baseline values, whereas 3-methylhistidine (p = 0.001), cortisol (p = 0.001) and adrenocorticotropic hormone (p = 0.004) levels were lower.

Conclusions
Regular intake of specific protein-enriched enteral formula increases plasma essential amino acids, especially branched-chain amino acids, and decreases cortisol and 3-methylhistidine, while plasma urea and creatinine remain unchanged.

Background
The proportion of the elderly is high and steadily rising in Western populations [1]. Aging is associated with an involuntary and progressive but physiological loss of muscle mass, designated sarcopenia [2], which is currently considered an emerging problem of Public Health [1]. Sarcopenia is accompanied by a reduction in strength and quality that leads to muscle weakness, limiting mobility and increasing vulnerability to injury [1,3]. Reduced muscle mass in older adults has also been associated with susceptibility to disease and decreased survival rates after critical illness [2].

Skeletal muscle is the body's main reservoir of amino acids, which contain 50-75% of human body proteins. Skeletal muscle is a vital supplier of amino acids for use as fuel by the brain and immune system and as a substrate for tissue repair during malnutrition, injury, and disease [4]. It is important to maintain the body protein mass in order to live well and remain physically independent.

It has been postulated that age-related muscle mass reduction is due to a multi-factorial process that include genetic and other factors such as cellular apoptosis, changes in protein metabolism, hormonal alterations, loss of neuromuscular function, inappropriate nutrition, lack of regular physical activity, and diseases or their sequelae [5]. The mechanisms underlying the loss of skeletal muscle are not clear but can be linked to a preceding disruption in the regulation of muscle protein turnover, specifically to an imbalance between protein synthesis and breakdown [6]. It has been demonstrated that the combination of prolonged inactivity and hypercortisolemia increases muscle protein catabolism and reduces muscle protein synthesis, even when substrates are available [6]. Likewise, hypercortisolemia has been observed in hypoalbuminemic individuals [7]. Albumin is a good marker of protein malnutrition, and lower concentrations are commonly observed in older subjects and have been associated with poor health outcomes and mortality [8].

Inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor alpha (TNF-α) contribute, together with a reduced concentration of growth factors, to the development of sarcopenia [1]. Insulin resistance (IR) is also implicated in sarcopenia and is frequently observed in elderly subjects, although it is mostly associated with obesity and, recently, with sarcopenic obesity [9].

Co-ingestion of protein and leucine stimulates muscle protein synthesis rates to the same extent in young and elderly lean men [10], and the intake of nutrients and proteins affects the albumin synthesis rate in humans [11]. Ingestion of 15 g/d of whey protein, containing 6.5 g of essential amino acids (EAA), has been reported to be strongly anabolic to skeletal muscle in healthy older individuals [12]. Enteral nutrition (EN) formulas are prescribed to elderly patients, when it is necessary, as an exclusive diet or in combination with other foods to achieve recommended dietary intakes. With this background, the aim of this study was to evaluate the effect of a six-month exclusive protein-enriched enteral diet with a relatively high content of branched-chain amino acids (BCAA) and other essential amino acids on albuminemia, cortisolemia, plasma amino acids, IR, and inflammation biomarkers in elderly patients subjected to total enteral nutrition.

http://www.nutritionandmetabolism.com/content/7/1/58