Nutrition and protein turnover in man

Nutritional Aspects of Wound Care

Malnutrition is a collective term that includes both undernutrition and malnutrition. Malnutrition presents with and without inflammation, is reported in underweight, normal weight, and overweight individuals, and is associated with undesirable alterations in body composition, and diminished functional status. Older adults commonly experience dwindling nutritional status as evidenced by insidious weight loss, insufficient dietary intake, loss of muscle mass, quality, and strength, declining functional status, and other physical and emotional decline indicators. Sustained pressure, acute trauma, malnutrition, and inflammatory-driven chronic conditions increase the risk for skin integrity issues.

Protein intake and muscle strength in older persons: does inflammation matter?

OBJECTIVES

To examine whether protein intake is associated with change in muscle strength in older persons. Because systemic inflammation has been associated with protein catabolism, the study also evaluated whether a synergistic effect exists between protein intake and inflammatory markers on change in muscle strength.

DESIGN

Longitudinal.

SETTING

The Invecchiare in Chianti Study.

PARTICIPANTS

Five hundred and ninety-eight older adults.

MEASUREMENTS

Knee extension strength was measured at baseline (1998-2000) and during 3-year follow-up (2001-2003) using a handheld dynamometer. Protein intake was assessed using a detailed food frequency questionnaire. The inflammatory markers examined were C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α).

RESULTS

The main effect of protein intake on change in muscle strength was not significant. However, a significant interaction was found between protein intake and CRP (P = .003), IL-6 (P = .049), and TNF-α (P = .02), indicating that lower protein intake was associated with greater decline in muscle strength in persons with high levels of inflammatory markers.

CONCLUSION

Lower protein intake was associated with decline in muscle strength in persons with high levels of inflammatory markers. These results may help to understand the factors contributing to decline in muscle strength with aging and to identify the target population of older persons who may benefit from nutritional interventions aimed at preventing or reducing age-associated muscle impairments and its detrimental consequences.

Is there evidence for an age-related reduction in metabolic rate?

To determine whether the age-related reduction in basal metabolic rate (BMR) is explained by a quantitative and/or qualitative change in the components of lean tissue, we conducted a cross-sectional study in groups of young (n = 38, 18-35 yr) and older (n = 24, 50-77 yr) healthy individuals. BMR was measured by indirect calorimetry. Body composition was obtained by using dual-energy X-ray absorptiometry (DEXA), which permitted four compartments to be quantified [bone mineral mass, fat mass (FM), appendicular lean tissue mass (ALTM), and nonappendicular lean tissue mass (NALTM)]. Absolute BMR and ALTM were lower, whereas FM was significantly higher in the older, compared with young, subjects. BMR, adjusted for differences in FM, ALTM, and NALTM, was significantly lower in the older subjects by 644 kJ/day. In separate regression analyses of BMR on body compartments, older subjects had significantly lower regression coefficients for ALTM and NALTM, compared with young subjects. Hence, the age-related decline in BMR is partly explained by a reduction in the quantity, as well as the metabolic activity, of DEXA-derived lean tissue components.

Effects of exaggerated amino acid and protein supply in man

A general update review of the dynamic aspect of protein metabolism is presented. The effect of excess protein level on protein metabolism has been the object of a limited number of studies in man. From the information available, it appears that the primary regulatory pathway for body protein homeostasis is the process of amino acid (protein) oxidation.

Effects of branched-chain amino acids on protein turnover

Amino acid availability rapidly regulates protein synthesis and degradation. Increasing amino acid concentrations above the levels found in post-absorptive plasma stimulates protein synthesis in a dose-dependent manner at the level of mRNA translation-initiation and inhibits protein degradation by inhibiting lysosomal autophagy. The anabolic effects of insulin on protein synthesis and protein degradation are exerted at the same sites (i.e., peptide chain initiation and lysosomal stabilization) allowing for a rapid synergistic response when both amino acids and insulin increase after a protein-containing meal. In perfused liver preparations, protein anabolic effects are exerted by a group of amino acids acting in concert. The BCAA are among the amino acids required for stimulation of hepatic protein synthesis, but there is no evidence that BCAA or leucine alone are effective. Leucine alone is an important inhibitor of hepatic protein degradation, but maximal inhibition requires in addition several other regulatory amino acids. In heart and skeletal muscle in vitro, increasing the concentration of the three BCAA or of leucine alone reproduces the effects of increasing the supply of all amino acids in stimulating protein synthesis and inhibiting protein degradation. Skeletal muscle is the largest repository of metabolically active protein and a major contributor to total body nitrogen balance. Supplying energy alone (i.e., carbohydrate and lipids) cannot prevent negative nitrogen balance (net protein catabolism) in animals or humans; only provision of amino acids allows the attainment of nitrogen balance. In rats and in humans nourished parenterally, provision of balanced amino acid solutions or of only the three BCAA cause similar improvements in nitrogen balance for several days. There is some evidence that infusions of leucine alone can stimulate muscle protein synthesis in vivo; the effect may be transitory and was not observed by all investigators; provisions of excess leucine alone does not seem to affect total body or muscle protein degradation in vivo. In postabsorptive rats, in vivo, infusion of the three BCAA together stimulates muscle protein synthesis as much as the infusion of a complete amino acid mixture or of a mixture of essential amino acids; the in vivo effect requires coinfusion of glucose or of small (physiological) doses of insulin, suggesting synergism between insulin and amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)