Normalizing resting energy expenditure across the life course in humans: challenges and hopes

Abstract

Whole-body daily energy expenditure is primarily due to resting energy expenditure (REE). Since there is a high inter-individual variance in REE, a quantitative and predictive framework is needed to normalize the data. Complementing the assessment of REE with data normalization makes individuals of different sizes, age, and sex comparable. REE is closely correlated with body mass suggesting its near constancy for a given mass and, thus, a linearity of this association. Since body mass and its metabolic active components are the major determinants of REE, they have been implemented into allometric modeling to normalize REE for quantitative differences in body weight and/or body composition. Up to now, various size and allometric scale laws are used to adjust REE for body mass. In addition, the impact of the anatomical and physical properties of individual body components on REE has been quantified in large populations and for different age groups. More than 80% of the inter-individual variance in REE is explained by FFM and its composition. There is evidence that the impact of individual organs on REE varies between age groups with a higher contribution of brain and visceral organs in children/adolescents compared with adults where skeletal muscle mass contribution is greater than in children/adolescents. However, explaining REE variations by FFM and its composition has its own limitations (inter-correlations of organs/tissues). In future, this could be overcome by re-describing the organ-to-organ variation using principal components analysis and then using the scores on the components as predictors in a multiple regression analysis.

Recent advances in understanding body weight homeostasis in humans

“…The drive to eat is related to the energy demand of FFM, but putative energy-demanding signals from skeletal muscle and from high-metabolic-rate organs like the liver, kidneys, heart, and brain still remain to be characterized. FFM is closely related to resting EE (REE; 17 ), and both REE and FFM are determinants of EI, hunger, and self-selected meal size 15 , 16 , 18 . With weight loss, REE and FFM decrease at a concomitant change in FFM composition with a disproportional loss in skeletal muscle mass compared with visceral organs like the liver and kidneys 13 , 14 .…”

Anthropometrics, diet, and resting energy expenditure in Norwegian adults with achondroplasia

“…Metabolically active tissues, such as skeletal muscle, brain, and liver, are the major contributors to REE (Mahan et al, ). However, when looking at REE per unit body weight, men and women with achondroplasia in the present study had REE/kg values similar to men and women of average height (Muller et al, ; Redman et al, ). This is inconsistent with the findings by Owen et al that achondroplastic individuals had higher REE/kg values compared to men and women of typical height (Owen et al, ).…”

“…The reasons underlying the predisposition for obesity in achondroplasia are unknown and could be related to excessive caloric intake or decreased energy expenditure (Hecht et al, ). The present study showed that Norwegian men and women with achondroplasia had lower daily REEs compared to those of average height (Muller et al, ; Owen et al, ; Owen et al, ; Redman et al, ). The mean REE was 1416 kcal/day for men and 1110 kcal/day for women.…”

Evolution of Resting Energy Expenditure, Respiratory Quotient, and Adiposity in Infants Recovering from Corrective Surgery of Major Congenital Gastrointestinal Tract Anomalies: A Cohort Study

“…Body mass in humans is strongly associated with the rate of heat production, as defined by REE [ 42 ]. In healthy adults, the major components of body mass differ in their metabolic rates, estimated as approximately 20 Kcal/kg for FFM and 5 Kcal/kg for FM [ 43 ]. The FFM, used as a measure of metabolically active tissue, is quite heterogeneous, comprised of organs and tissues with different cellular components [ 42 , 43 ].…”

“…In healthy adults, the major components of body mass differ in their metabolic rates, estimated as approximately 20 Kcal/kg for FFM and 5 Kcal/kg for FM [ 43 ]. The FFM, used as a measure of metabolically active tissue, is quite heterogeneous, comprised of organs and tissues with different cellular components [ 42 , 43 ]. The total body REE is the sum of the individual organ and tissue REEs, and each organ and tissue has unique mass-specific metabolic rate [ 42 ].…”