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Abstract: Research suggests that changes in leucine oxidation (leuox) with feeding may reflect adult protein requirements. We evaluated this possibility by assessing the effects of age, sex, and different protein intakes on whole-body leucine kinetics and nitrogen balance. Thirty-four young (n=18, 22–46 years) and old (n=16, 63–81 years) men and women completed three 18-day trials with protein intakes of 0.50, 0.75 and 1.00 g protein·kg body weight−1·d−1. Fasting and fed-state leucine kinetics were quantified on day 12 of each trial using a primed, constant infusion of L-[1-13C]leucine. Protein requirement was estimated using classical nitrogen balance measurements and calculations. Leucine kinetics parameters were influenced by age and sex across all protein intakes. With feeding, leuox increased more in old vs. young adults. Independent of age, fasting and fed-state leuox were lower, and net leucine balance (fasting+fed-state) was higher in women vs. men. Among all subjects and protein intakes, nitrogen balance was correlated with fed-state leuox (r=0.39), fed-state leucine balance (r=0.60), net leucine balance (r=0.49) and the change in leuox from the fasting to fed state (r=0.49) (P<.05 for all results). At the highest protein intake, the change in leuox with feeding was inversely correlated with protein requirement (r=−0.39). These findings indicate that leucine kinetics, especially leuox, reflect nitrogen balance-based estimates of the need for dietary protein and generally support the view that protein requirement is comparable between young and old adults. [Copyright &y& Elsevier]

Abstract: Inadequate protein intake initiates adverse changes in skeletal muscle function and structure (i.e., an accommodative response). mRNA level changes due to short-term inadequate dietary protein might be an early indication of subsequent accommodation. The aims of this study were to assess the effects of dietary protein and the diet-by-age interaction on the skeletal muscle transcriptome. Twelve younger (21–43 y) and 10 older (63–79 y) men completed three controlled feeding trials with protein intakes of 0.50 (LPro: lower protein), 0.75 (MPro: medium protein) and 1.00 g protein·kg body weight−1·day−1 (HPro: higher protein). A fasting state biopsy was taken on Day 12 of each trial. Global changes in transcript levels were assessed with Affymetrix genechips and expression patterns determined using self-organizing maps. Nine hundred fifty-eight transcripts were differentially expressed (P<.05) by diet and 853 had a diet-by-age interaction (P<.05). The results for diet alone revealed that LPro was associated with up-regulation of transcripts related to ubiquitin-dependent protein catabolism and muscle contraction and LPro and MPro resulted in up-regulation of transcripts related to apoptosis and down-regulation of transcripts related to cell differentiation, muscle and organ development, extracellular space and responses to stimuli and stress. The diet-by-age effect on protein modification transcripts was consistent with the older males being less responsive to anabolic stimuli (lower protein synthesis at HPro) and more responsive to a catabolic state (protein breakdown at LPro). Changes in skeletal muscle mRNA levels in younger and older males to protein intake near or below the recommended dietary allowance are indicative of an early accommodative response. [Copyright &y& Elsevier]

Abstract: This study assessed the effects of combined chromium picolinate (CP) and conjugated linoleic acid (CLA) supplementation on energy restriction and exercise-induced changes in body composition, glucose metabolism, lipid lipoprotein profile and blood pressure in overweight, premenopausal women. For 12 weeks, 35 women [age 36±1 years (mean±S.E.M.); BMI 28.0±0.5 kg/m2] were counseled to consume a 2092 kJ/day (500 kcal/day) energy deficit diet and performed 30 min of moderate-intensity walking or jogging 5 days/week. The women were randomly assigned to ingest either CP-CLA [400 μg chromium (Cr), 1.8 g CLA in 2.4 g tonalin oil, n=19] or placebo (<0.1 μg Cr, 2.4 g canola oil, n=16). Compared to baseline, urinary Cr excretion increased 22-fold, plasma CLA isomer 18:2 (c9,t11) content increased 79% and plasma CLA isomer 18:2 (t10,c12) became detectable in CP-CLA and were unchanged in Placebo. Over time, body weight decreased 3.5±0.5% (CP-CLA −2.6±0.5; placebo −2.5±0.5 kg) and fat mass decreased 8.9±1.3% (CP-CLA −2.7±0.5, placebo −2.4±0.5 kg), with no differences in responses between groups. Fasting blood hemoglobin A1c, plasma glucose and insulin, a homeostatic assessment of insulin resistance, serum total cholesterol (CHOL), high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol, triacylglycerol (TG), CHOL/HDL ratio, TG/HDL ratio and sitting systolic and diastolic blood pressures were not changed over time or influenced by CP-CLA. The use of a combined CP and CLA supplement for 3 months does not affect diet- and exercise-induced changes in weight and body composition or improve indexes of metabolic and cardiovascular health in young overweight women. [Copyright &y& Elsevier]