Brown Adipose Tissue: A New Human Organ?

Shalini Ojha; Mark Birtwistle; Helen Budge; Michael E Symonds

Disclosures

Expert Rev Endocrinol Metab. 2013;8(2):123-125. 

In This Article

Diet-induced Thermogenesis

Diet-induced thermogenesis (DIT) is the metabolic cost of processing food. Its obligatory component is the energy spent in digestion and assimilation of food. In addition, there may be a facultative component, possibly mediated by BAT, which generates additional heat and has been described as a special mechanism for extra energy dissipation in response to overnutrition.[5]

Although the role of BAT in DIT has been highly controversial, some new findings were presented at the meeting which support the case for BAT involvement. Studies are required to be conducted at thermoneutral temperatures in order to remove the confounding effect of thermogenesis induced by the relatively cool environment for rodents that are maintained in standard animal house temperatures (21–23°C). Studies at thermoneutrality found that mice fed with a high-fat diet recruit BAT, have higher oxygen consumption and enhanced response to norepinephrine. By contrast, UCP1 knockout mice do not demonstrate such changes. These findings, therefore, illustrate that signaling processes triggered by overfeeding can enhance BAT recruitment and activation and induce increased energy expenditure. However, high-fat diets or hyperphagia are not sufficient to recruit BAT by themselves and the role of the type of fat and other nutrients in the diet remains unresolved. It was also suggested that DIT might be 'obesity induced thermogenesis', wherein signals from WAT could act to promote the recruitment and thermogenesis in BAT.

Further support for the existence of DIT was presented in studies of imaging BAT in humans. Both thermal imaging and PET-computed tomography (CT) studies in humans have demonstrated some evidence to support the increased activation of BAT in response to meals.

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