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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #37496
Title: PROTEIN TURNOVER AND ENERGY METABOLISM OF ELDERLY WOMEN CHRONICALLY FED A LOW PROTEIN DIET

Author
item CASTANEDA CARMEN - TUFTS-HNRCA
item DOLNIKOWSKI GREG - TUFTS-HNRCA
item DALLAL GERARD E - TUFTS-HNRCA
item EVANS W F - PENN STATE
item CRIM MARILYN C - TUFTS-HNRCA

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: The human body adapts to marginal or low protein intake levels by sparing its use of amino acids which are the protein constituents. Since dietary amino acids are not stored in the body, they are used in the synthesis of new proteins or excreted (oxidation) in urine as nitrogen, or in expired air as CO2. Protein turnover represents the dynamics of synthesis and oxidation. It is a process that requires energy and that can be affected by stress or diseases. In this study, two levels of dietary protein, normal and low, were fed to elderly women for 10 weeks to determine the influence of normal and low dietary protein levels on protein turnover (synthesis and oxidation), and the effects of stress on protein turnover. We observed that protein turnover was lower in the low protein group than in the high protein group, while synthesis was kept about the same in both diet groups. Although decreases in oxidation allowed for some protein-sparing effect when dietary protein was low, it was not enough to prevent losses in body composition and functional capacity. This implies that there may be an obligatory minimum level of oxidation below which the human body can no longer adapt to a low protein diet without some physiological cost. The energy cost of protein turnover was not different between diet groups. There were no differences in the response of protein turnover after stress in either diet group. These results indicate that oxidation may be a good index of protein nutritional status in elderly populations; however further research is needed.

Technical Abstract: The metabolic mechanisms of accommodation to a low protein diet in elderly women were studied. Diets containing 1.47 (low) or 2.94 g protein.kg body cell mass**-1.d**-1 (0.45 or 0.92 g.kg body weight**-1.d**-1), respectively, were fed for 10 weeks. Nitrogen balance, leucine kinetics, resting metabolic rate, and acute-phase responses were measured. In the low protein group, leucine flux and oxidation were lower after 3 weeks, and continued to decrease through- out the 10-week study and were correlated with improvement in nitrogen balance. There were no changes in metabolic rate within or between diets, except when metabolic rate was related to protein oxidation and flux in the adequate protein diet only. There were no differences in the acute-phase response. Protein oxidation was a more sensitive index of protein nutritional status than synthesis, flux, metabolic rate or acute-phase response.