Obesity Tissue: Composition, Energy Expenditure, and Energy Content in Adult Humans

Abstract

Objective Chronic positive energy balance leads to obesity, and the “excess” weight is usually described as consisting solely of adipose tissue (AT) or its two components, fat and fat‐free mass (nonfat cell mass, extracellular fluid). This study aimed to clarify the nature of “obesity” tissue. Methods A total of 333 adults had AT, skin, skeletal muscle, bone, heart, liver, kidney, spleen, brain, and residual mass measured or derived using magnetic resonance imaging and dual‐energy x‐ray absorptiometry. First, associations between these components and AT were examined by developing multiple regression models. Next, obesity‐tissue composition was developed by deriving mean component mass differences between participant groups with normal weight (BMI < 25 kg/m2) and those with obesity (BMI > 29.9 kg/m2); respective resting energy expenditures and metabolizable energy and protein contents were calculated. Results AT significantly predicted organ‐tissue mass in 17 of 18 multiple regression models. In addition to AT and skeletal muscle, the following associations were found: skin, liver, and bone were main contributors to obesity‐tissue composition; liver, kidneys, and heart to resting energy expenditure; and skin, liver, and bone to metabolizable energy and protein contents. A pronounced sexual dimorphism was present in all three models. Conclusions Obesity is characterized not only by excess AT but by increases in the masses of other “companion” organs and tissues and their related metabolic properties.

Allometric models of adult regional body lengths and circumferences to height: Insights from a three‐dimensional body image scanner

“…Our findings combined with those of Hwaung et al () found the largest proportion increase in taller individuals come from legs. It was hypothesized in Hwaung et al () that these disproportionate increases may be due to lengths of leg bones representing a higher proportion of height in taller individuals. Scaling exponents for leg lengths were larger than 1 for both males and females supporting this conjecture (K and L in Table ).…”

“…Since, thigh circumference scales to the power of ∼0.64 in males and ∼0.68 in females, the scaling exponent of cross‐sectional area will be twice these values; 1.28 in males and 1.35 in females. This calculation provides evidence to support the Hwaung et al () conjecture that taller individuals increase with larger cross‐sectional leg area than compared to their shorter counterparts. This finding is consistent with those found in Bjornerem et al ().…”

“…Scaling exponents for leg lengths were larger than 1 for both males and females supporting this conjecture (K and L in Table ). It was also hypothesized in Hwaung et al () that leg bone cross‐sectional areas should disproportionately increase to support higher total mass and protect against fracture. Here we cannot estimate leg bone cross‐sectional areas, but we can estimate the scaling exponent of leg cross‐sectional area by using thigh circumference.…”

“…Body mass also increases across adults as a function of adiposity level. Several different lines of investigation focus on the nature of adiposity tissue, the body mass accounted for after controlling for age and height (Hwaung et al, ).…”

Simple Skeletal Muscle Mass Estimation Formulas: What We Can Learn From Them

“…Second, greater adiposity (i.e., %fat) is also accompanied by enlargement of the SM compartment (12). People who are obese have more SM for their age and height than people who are normal weight (12).…”