Contribution of individual organ mass loss to weight loss-associated decline in resting energy expenditure.
BACKGROUND
Weight loss leads to reduced resting energy expenditure (REE) independent of fat-free mass (FFM) and fat mass (FM) loss, but the effect of changes in FFM composition is unclear.


OBJECTIVE
We hypothesized that a decrease in REE adjusted for FFM with weight loss would be partly explained by a disproportionate loss in the high metabolic activity component of FFM.


METHODS
Forty-five overweight and obese women [body mass index (in kg/m(2)): 28.7-46.8] aged 22-46 y followed a low-calorie diet for 12.7 +/- 2.2 wk. Body composition was measured by magnetic resonance imaging, dual-energy X-ray absorptiometry, and a 4-compartment model. REE measured by indirect calorimetry (REEm) was compared with REE calculated from detailed body-composition analysis (REEc) by using specific organ metabolic rates (ie, organ REE/mass).


RESULTS
Weight loss was 9.5 +/- 3.4 kg (8.0 +/- 2.9 kg FM and 1.5 +/- 3.1 kg FFM). Decreases in REE (-8%), free triiodothyronine concentrations (-8%), muscle (-3%), heart (-5%), liver (-4%), and kidney mass (-6%) were observed (all P < 0.05). Relative loss in organ mass was significantly higher (P < 0.01) than was the change in low metabolically active FFM components (muscle, bone, and residual mass). After weight loss, REEm - REEc decreased from 0.24 +/- 0.58 to 0.01 +/- 0.44 MJ/d (P = 0.01) and correlated with the decrease in free triiodothyronine concentrations (r = 0.33, P < 0.05). Women with high adaptive thermogenesis (defined as REEm - REEc < -0.17 MJ/d) had less weight loss and conserved FFM, liver, and kidney mass.


CONCLUSIONS
After weight loss, almost 50% of the decrease in REEm was explained by losses in FFM and FM. The variability in REEm explained by body composition increased to 60% by also considering the weight of individual organs.
Bosy-Westphal
Anja
A
Institute of Human Nutrition and Food Science, Christian-Albrechts University, Kiel, Germany.
Kossel
Elke
E
Goele
Kristin
K
Later
Wiebke
W
Hitze
Britta
B
Settler
Uta
U
Heller
Martin
M
Glüer
Claus-Christian
CC
Heymsfield
Steven B
SB
Müller
Manfred J
MJ
D000273:Adipose Tissue / Q000378:metabolism*; D000328:Adult; D001825:Body Fluid Compartments / Q000502:physiology*; D004038:Diet, Reducing; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism; D009929:Organ Size / Q000502:physiology*; D050177:Overweight / Q000378:metabolism*; D012146:Rest; D022722:Thermogenesis / Q000502:physiology; D014284:Triiodothyronine / Q000097:blood; D015431:Weight Loss / Q000502:physiology*; D055815:Young Adult
D014284:Triiodothyronine