Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

Pathophysiology of Human Visceral Obesity: An Update

A single abdominal cross-sectional computerized axial tomography and magnetic resonance image is often obtained in studies examining adipose tissue (AT) distribution. An abdominal image might also provide additional useful information on total body skeletal muscle (SM) and AT volumes with related physiological insights. We therefore investigated the relationships between abdominal SM and AT areas from single images and total body component volumes in a large and diverse sample of healthy adult subjects. Total body SM and AT volumes were derived by whole body multislice magnetic resonance imaging in 123 men [age (mean ± SD) of 41.6 ± 15.8 yr; body mass index of 25.9 ± 3.4 kg/m2] and 205 women (age of 47.8 ± 18.7 yr; body mass index of 26.7 ± 5.6 kg/m2). Single abdominal SM and AT slice areas were highly correlated with total body SM (r = 0.71–0.92; r = 0.90 at L4–L5 intervertebral space) and AT (r = 0.84–0.96; r = 0.94 at L4–L5 intervertebral space) volumes, respectively. R2 increased by only 5.7–6.1% for ...

https://www.focusopvoeding.nl/wp-content/uploads/2016/02/Shen-2004-total-body-skeletal-muscle-and-adipose-tissue-volumes-estimation-from-a-single-abdominal-cross-sectional.pdf

Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image

Obesity is prevalent in the U.S. population and contributes significantly to morbidity and mortality. Treatments include behavioral therapy, pharmacotherapy, and bariatric surgery. Some sequelae of obesity are reversed with weight loss. Maintaining weight loss is a challenge.

https://www.nejm.org/doi/pdf/10.1056/NEJMra1514009

Mechanisms, Pathophysiology, and Management of Obesity

Obesity is a critical risk factor for the development of type 2 diabetes (T2D), and its prevalence is rising worldwide. White adipose tissue (WAT) has a crucial role in regulating systemic energy homeostasis. Adipose tissue expands by a combination of an increase in adipocyte size (hypertrophy) and number (hyperplasia). The recruitment and differentiation of adipose precursor cells in the subcutaneous adipose tissue (SAT), rather than merely inflating the cells, would be protective from the obesity-associated metabolic complications. In metabolically unhealthy obesity, the storage capacity of SAT, the largest WAT depot, is limited, and further caloric overload leads to the fat accumulation in ectopic tissues (e.g., liver, skeletal muscle, and heart) and in the visceral adipose depots, an event commonly defined as “lipotoxicity.” Excessive ectopic lipid accumulation leads to local inflammation and insulin resistance (IR). Indeed, overnutrition triggers uncontrolled inflammatory responses in WAT, leading to chronic low-grade inflammation, therefore fostering the progression of IR. This review summarizes the current knowledge on WAT dysfunction in obesity and its associated metabolic abnormalities, such as IR. A better understanding of the mechanisms regulating adipose tissue expansion in obesity is required for the development of future therapeutic approaches in obesity-associated metabolic complications.

Adipose Tissue Dysfunction as Determinant of Obesity-Associated Metabolic Complications

Gender differences in insulin resistance, body composition, and energy balance.

Recent advances in imaging techniques and understanding of differences in the molecular biology of adipose tissue has rendered classical anatomy obsolete, requiring a new classification of the topography of adipose tissue. Adipose tissue is one of the largest body compartments, yet a classification that defines specific adipose tissue depots based on their anatomic location and related functions is lacking. The absence of an accepted taxonomy poses problems for investigators studying adipose tissue topography and its functional correlates. The aim of this review was to critically examine the literature on imaging of whole body and regional adipose tissue and to create the first systematic classification of adipose tissue topography. Adipose tissue terminology was examined in over 100 original publications. Our analysis revealed inconsistencies in the use of specific definitions, especially for the compartment termed “visceral” adipose tissue. This analysis leads us to propose an updated classification of total body and regional adipose tissue, providing a well-defined basis for correlating imaging studies of specific adipose tissue depots with molecular processes.

/pdf/adipose-tissue-quantification-by-imaging-methods-a-proposed-o8jsltig3s.pdf

Adipose Tissue Quantification by Imaging Methods: A Proposed Classification

Objective: To compare the accuracy of four volume estimation models to actual tissue and organ volumes measured in the visible woman.



Methods: Actual volumes were calculated from 1-mm-thick visible woman images that were segmented for five major components including subcutaneous and visceral adipose tissue across the 1730 available slices. Four available models resolved to two equations: truncated cone/truncated pyramid vs. two-column/parallel trapezium. Between-slice interval and initial slice were systematically varied when deriving component volumes using the two equations in four regions.



Results: For each compartment and each between-slice interval, the means of the two-column model were always the same as the corresponding reference volumes, whereas those of the truncated cone model were smaller than the reference volumes. Similarly, the coefficient variation for the two-column model was always smaller than for the truncated cone model.



Discussion: The equation based on the parallel trapezium and the two-column models is more accurate in estimating tissue volumes than the corresponding equation for truncated pyramid and truncated cone models. This finding has important implications for the volume calculations of imaging-based body compartments such as adipose tissue.

Volume estimates by imaging methods: model comparisons with visible woman as the reference.

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Adipose Tissue Quantification by Imaging Methods: A Proposed Classification

Volume estimates by imaging methods: model comparisons with visible woman as the reference.