Brain and high metabolic rate organ mass: contributions to resting energy expenditure beyond fat-free mass.
BACKGROUND
The degree to which interindividual variation in the mass of select high metabolic rate organs (HMROs) mediates variability in resting energy expenditure (REE) is unknown.


OBJECTIVE
The objective was to investigate how much REE variability is explained by differences in HMRO mass in adults and whether age, sex, and race independently predict REE after adjustment for HMRO.


METHODS
A cross-sectional evaluation of 55 women [30 African Americans aged 48.7 +/- 22.2 y (mean +/- SD) and 25 whites aged 46.4 +/- 17.7 y] and 32 men (8 African Americans aged 34.3 +/- 18.2 y and 24 whites aged 51.3 +/- 20.6 y) was conducted. Liver, kidney, spleen, heart, and brain masses were measured by magnetic resonance imaging, and fat and fat-free mass (FFM) were measured by dual-energy X-ray absorptiometry. REE was measured by indirect calorimetry.


RESULTS
REE estimated from age (P = 0.001), race (P = 0.006), sex (P = 0.31), fat (P = 0.001), and FFM (P < 0.001) accounted for 70% (adjusted (2)) of the variability in REE. The addition of trunk HMRO (P = 0.001) and brain (P = 0.006) to the model increased the explained variance to 75% and rendered the contributions of age, sex, and race statistically nonsignificant, whereas fat and FFM continued to make significant contributions (both P < 0.05). The addition of brain to the model rendered the intercept (69 kcal . kg(-1) . d(-1)) consistent with zero, which indicated zero REE for zero body mass.


CONCLUSIONS
Relatively small interindividual variation in HMRO mass significantly affects REE and reduces the role of age, race, and sex in explaining REE. Decreases in REE with increasing age may be partly related to age-associated changes in the relative size of FFM components.
Javed
Fahad
F
New York Obesity Nutrition Research Center, St Luke's-Roosevelt Hospital, New York, NY, USA.
He
Qing
Q
Davidson
Lance E
LE
Thornton
John C
JC
Albu
Jeanine
J
Boxt
Lawrence
L
Krasnow
Norman
N
Elia
Marinos
M
Kang
Patrick
P
Heshka
Stanley
S
Gallagher
Dympna
D
D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000378:metabolism*; D000328:Adult; D001741:Black or African American; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001481:Basal Metabolism; D001825:Body Fluid Compartments / Q000378:metabolism*; D001921:Brain / Q000033:anatomy & histology*; D002153:Calorimetry, Indirect; D003430:Cross-Sectional Studies; D005260:Female; D006321:Heart / Q000033:anatomy & histology; D006801:Humans; D007668:Kidney / Q000033:anatomy & histology; D008099:Liver / Q000033:anatomy & histology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009929:Organ Size / Q000502:physiology*; D012737:Sex Factors; D013154:Spleen / Q000033:anatomy & histology; D044465:White People; D055815:Young Adult