Brown adipose tissue as a regulator of energy expenditure and body fat in humans - PubMed (original) (raw)

Brown adipose tissue as a regulator of energy expenditure and body fat in humans

Masayuki Saito. Diabetes Metab J. 2013 Feb.

Abstract

Brown adipose tissue (BAT) is recognized as the major site of sympathetically activated nonshivering thermogenesis during cold exposure and after spontaneous hyperphagia, thereby controling whole-body energy expenditure and body fat. In adult humans, BAT has long been believed to be absent or negligible, but recent studies using fluorodeoxyglucose-positron emission tomography, in combination with computed tomography, demonstrated the existence of metabolically active BAT in healthy adult humans. Human BAT is activated by acute cold exposure, being positively correlated to cold-induced increases in energy expenditure. The metabolic activity of BAT differs among individuals, being lower in older and obese individuals. Thus, BAT is recognized as a regulator of whole-body energy expenditure and body fat in humans as in small rodents, and a hopeful target combating obesity and related disorders. In fact, there are some food ingredients such as capsaicin and capsinoids, which have potential to activate and recruit BAT via activity on the specific receptor, transient receptor potential channels, thereby increasing energy expenditure and decreasing body fat modestly and consistently.

Keywords: Adipose tissue, brown; Capsinoids; Cold exposure; Energy expenditure; Non-shivering thermogenesis; Obesity; Transient receptor potential channel.

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Conflict of interest statement

No potential conflict of interest relevant to this article was reported.

Figures

Fig. 1

Fig. 1

Sympathetically activated thermogenesis in brown adipose tissue, lipid mobilization from white adipose tissue, and induction of beige cells. Sympathetic nerve activity in adipose tissues is increased in response to cold exposure and oral ingestion of some food ingredients through the activation of transient receptor potential channels (TRP). Noradrenaline binds to β-adrenergic receptors (βAR) and initiates signaling cascades for triglyceride (TG) hydrolysis. The released fatty acids activate uncoupling protein 1 (UCP1) and are oxidized to serve as an energy source of thermogenesis. Activated UCP1 uncouples oxidative phosphorylation from ATP synthesis and dissipates energy as heat. Chronic sympathetic activation produces not only brown fat hyperplasia but also an induction of beige cells in white fat, thereby increasing whole-body energy expenditure and decreasing body fat.

Fig. 2

Fig. 2

Human brown adipose tissue detected by fluorodeoxyglucose (FDG)-positron emission tomography (PET). FDG uptake into adipose tissue at the supraclavicular and paraspinal regions is detected by PET. The FDG uptake into adipose tissues is negligible under a warm condition at 27℃ (A), but increases greatly after exposure to cold at 19℃ (B) for 2 hours.

Fig. 3

Fig. 3

Age-related decrease in brown adipose tissue (BAT) and accumulation of body fat. The activity and prevalence of BAT decrease and body fat increases with age, suggesting the activation and recruitment of BAT as an effective regimen to prevent the age-related development of obesity.

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