Whole-body and muscle protein metabolism are not affected by acute deviations from habitual protein intake in older men: the Hormonal Regulators of Muscle and Metabolism in Aging (HORMA) Study.

BACKGROUND: Acute deviations in protein intake before the quantification of protein kinetics in older humans may explain the controversy over the effects of older age on muscle protein synthesis and proteolysis rates. OBJECTIVE: We hypothesized that an acute decrease in protein intake from the habitual intake is associated with lower muscle protein synthesis and higher proteolysis rates, whereas an acute increase in protein intake from the habitual intake is associated with higher muscle protein synthesis and lower proteolysis rates. DESIGN: In 112 community-dwelling healthy men aged 65-90 y, we quantified resting whole-body [1,2-(13)C(2)]leucine kinetics, muscle mixed protein fractional synthesis rates (FSRs), and muscle proteasome proteolytic enzyme activities after participants consumed for 3 d controlled research meals (0.9-1.1 g protein · kg(-1) · d(-1)) that contained more or less protein than that habitually consumed and that induced alterations in nitrogen balance. RESULTS: Protein kinetic parameters were not significantly different between the groups, despite controlled research protein intakes that were lower (-0.2 to -0.3 g · kg(-1) · d(-1)) or higher (+0.2 g · kg(-1) · d(-1)) than habitual intakes and that induced negative (-22 to -25 mg · kg(-1) · d(-1)) or positive (22-25 mg · kg(-1) · d(-1)) nitrogen balance. Within these acutely altered protein intake and nitrogen balance boundaries, a reduction in protein intake from habitual intake and induction of negative nitrogen balance were not associated with higher proteolysis or lower muscle FSR, and an acute increase in protein intake from habitual intake and induction of positive nitrogen balance were not associated with lower proteolysis or higher muscle FSR. A higher quantitative insulin sensitivity check index was associated with lower whole-body proteolysis rates. CONCLUSIONS: The practice of acutely controlling protein intake, even at intakes lower than habitual intakes that induce negative nitrogen balance, before quantifying human protein kinetics does not significantly reduce muscle protein synthesis or increase proteolysis. Factors other than protein intake explain lower muscle protein synthesis rates with advanced age. This trial is registered at clinicaltrials.gov as NCT00183040.

How can statistical approaches enhance transdisciplinary study of drug misuse prevention?

Application of statistical techniques in transdisciplinary research includes statistical model selection and model specification. This paper presents statistical models used in drug misuse prevention research. The historical roots of these models are discussed to illustrate the numerous disciplines from which different techniques originated. Single and multilevel approaches are described to illustrate methods of synthesizing perspectives from different scientific arenas. Using single-level approaches in transdisciplinary research, these models can easily incorporate broader theoretical considerations and more integrated hypotheses by representing each discipline with a set of variables. Simultaneous testing of every set of variables obtained from different disciplines may provide more comparable results to identify critical factors associated with substance-use behavior. Using multilevel approaches, more powerful syntheses across disciplines can be achieved by representing each discipline at a different level.