Effect of Constitution on Mass of Individual Organs and Their Association with Metabolic Rate in Humans—A Detailed View on Allometric Scaling

Resting energy expenditure (REE)-power relationships result from multiple underlying factors including weight and height. In addition, detailed body composition, including fat free mass (FFM) and its components, skeletal muscle mass and internal organs with high metabolic rates (i.e. brain, heart, liver, kidneys), are major determinants of REE. Since the mass of individual organs scales to height as well as to weight (and, thus, to constitution), the variance in these associations may also add to the variance in REE. Here we address body composition (measured by magnetic resonance imaging) and REE (assessed by indirect calorimetry) in a group of 330 healthy volunteers differing with respect to age (17–78 years), sex (61% female) and BMI (15.9–47.8 kg/m2). Using three dimensional data interpolation we found that the inter-individual variance related to scaling of organ mass to height and weight and, thus, the constitution-related variances in either FFM (model 1) or kidneys, muscle, brain and liver (model 2) explained up to 43% of the inter-individual variance in REE. These data are the first evidence that constitution adds to the complexity of REE. Since organs scale differently as weight as well as height the “fit” of organ masses within constitution should be considered as a further trait

Percentage mean deviations and variances of body composition parameters and REE between measured and calculated values (n = 260) (means, range).

<p>DXA, Dual X-ray Absorptiometry; FM, fat mass; FFM, fat-free mass; MM, muscle mass; MRI, Magnetic Resonance Imaging; REE, resting energy expenditure, SEE, standard error of the estimate.</p><p>Calculation was based on functions as derived from three dimensional plots as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022732#pone-0022732-g001" target="_blank">Fig. 1</a>.</p

Masses of brain, heart, liver, kidneys and spleen plotted against height and weight for men (a,c,e,g,i) and women (b.d,f,h,j).

<p>Masses of brain, heart, liver, kidneys and spleen plotted against height and weight for men (a,c,e,g,i) and women (b.d,f,h,j).</p

Characterisation of the study population: anthropometric data, prevalence of overweight and obesity, body composition and resting energy expenditure (means ±SD, range) (n = 262).

<p>*p<0.01 for sex differences (t-Test).</p><p>BMI, body mass index; WC, waist circumference; DXA, Dual Energy X-ray Absorptiometry; FM, fat mass; FFM, fat-free mass; MM, muscle mass; MRI, Magnetic Resonance Imaging; REE, resting energy expenditure, REEadj, resting energy expenditure adjusted for FFM, SEE, standard error of the estimate.</p

REE plotted against height and weight for men and women.

<p>REE plotted against height and weight for men and women.</p