ABSTRACT
The rediscovery of nonshivering thermogenesis (NST) that initiates in specialized fat cells called brown adipocytes in brown and beige adipose tissue (BAT) in adult humans prompted significant interest in the potential to harness NST as a treatment for obesity and metabolic dysfunction. It is clear that sympathetic activation, for example, induced by cold exposure, can stimulate the proliferation and differentiation of BAT as well as upregulation of NST in those cells. However, it is less clear how NST fits into overall energy metabolism. Energy expenditure in BAT should be subject to energetic tradeoffs and constraints, consistent with life history theory. This chapter outlines how BAT abundance and metabolic activity change across the life course, including during childhood and adolescent growth, pregnancy and lactation, and aging. Studies from humans and from animal models are reviewed to illustrate how BAT is affected by positive and negative energy balance (e.g., under- and overnutrition), exercise, and long-term stress. The chapter concludes with a discussion of the role of BAT in hominin expansion to cold climates and provides suggestions for future research directions to better understand the evolutionary importance of this unique fat depot.
