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Aerobic fitness level does not modulate changes in nitrogen balance produced by unaccustomed increases in energy expenditure
Author(s) -
Smith Tracey J,
Pikosky Matt,
Grediagin Ann,
Karl James P,
Caruso Christina,
McClung Holly,
Mathow Mona,
Stanger Michael,
Glickman Ellen
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.lb82-b
Subject(s) - sed , energy expenditure , zoology , aerobic exercise , chemistry , medicine , endocrinology , biology
An unaccustomed increase in energy expenditure (EE) causes transient increases in whole‐body nitrogen (N) loss in sedentary (SED) persons, but whether a high aerobic fitness level confers protection against this catabolic response is unknown. We compared changes in NBAL accompanying 1000 kcal/d increase in EE in SED and higher fitness level (FIT) volunteers. Seven SED (VO 2 peak 39 ± 3 [± SD] ml.kg −1 min −1 ; 22 ± 3 yr) and 8 FIT (VO 2 peak 56 ± [± 7 SD] ml.kg −1 min −1 ; 24 ± 5 yr) men increased EE 1000 kcal/d (aerobic exercise at 50–65% VO 2peak ) for 7‐d, following 4‐d baseline (BL) of normal EE (per pre‐study activity record). Volunteers followed a pre‐study (3‐d) stabilization diet, and consumed an energy sufficient diet (55% carbohydrate and 0.9 g pro/kg body weight) throughout the study. Daily N intake was determined by computer‐based nutrient analysis (ESHA Research, Salem, OR), and N output was calculated daily by measured N in 24‐h collections of sweat, urine and feces, and estimated insensible losses. Subjects lived on site, and EE was assessed by open‐circuit spirometry. NBAL was similar for FIT and SED throughout increased EE. FIT and SED showed an increase in NBAL from D5‐8 to D9‐11, P<0.05 (i.e. FIT: −0.6 ± 1.9 g N/d, 0.3 ± 1.9 g N/d and SED: −0.8 ± 1.4 g N/d, 0.4 ± 1.0 g N/d). The similar time course and magnitude of NBAL changes for SED and FIT males suggest that aerobic fitness does not confer adaptations to unaccustomed increases in energy expenditure. Research funded by MRMC.