A Marker of Ectopic Fat Deposition?Defining CMR - Intra-abdominal Adipose Tissue: the Culprit?
Individuals vary in terms of how they store fat in response to a positive energy balance. However, the factors underpinning these differences are poorly understood. Excess visceral fat may be a marker of the inability of subcutaneous adipose tissue to act as an “energy sink” for surplus calories resulting from excess energy intake and/or reduced energy expenditure. The inability of subcutaneous fat to store excess energy may cause fat to accumulate at undesirable locations such as the liver, skeletal muscle, heart, and even in pancreatic beta cells. This phenomenon has been described as ectopic fat deposition. In this regard, many of the metabolic complications found in individuals with excess visceral fat have also been found in those with a fatty liver and ectopic fat. Although liver fat has been frequently linked to excess visceral fat, several studies have shown that liver fat and visceral fat each contribute independently to the metabolic complications of abdominal obesity.
- Non-alcoholic fatty liver disease is a common cause of chronic liver disease and is closely associated with a range of cardiometabolic risk factors as well as diabetes and mortality risk.
- It is unknown how liver fat develops but a number of plausible mechanisms have been proposed, including “spillover” of excess energy from adipose tissue, adiponectin deficiency, a high-fat diet, and/or overactivation of the endocannabinoid system.
- Increased liver fat storage is related to hepatic insulin resistance and increased synthesis and secretion of atherogenic lipoproteins.
- The gold standard method for quantifying liver fat is liver biopsy.
- However, imaging techniques such as magnetic resonance spectroscopy (MRS) and computed tomography (CT) are safe and reliable alternatives.
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Respective Roles of Visceral Fat and Liver Fat
- Visceral fat and liver fat are independently related to health risk. However, visceral fat is generally the stronger predictor of metabolic abnormalities, morbidity, and mortality.
- While the portal theory suggests that visceral fat and increased liver fat deposition are linked, the evidence for such a relationship is equivocal.
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