Abstract

Brown adipose tissue (BAT) and beige adipocytes dissipate energy as heat and act as metabolic sinks for glucose 
and lipids. Their activation improves insulin sensitivity, lowers ectopic fat, and protects against cardiometabolic 
disease. In obesity, however, thermogenic capacity declines due to impaired BAT recruitment, defective 
browning of white adipose tissue (WAT), mitochondrial dysfunction, and chronic inflammation, a state of 
“thermogenic failure.” This failure reduces whole-body energy expenditure and promotes positive energy 
balance, but also removes a critical buffer that normally clears circulating nutrients and releases beneficial 
cytokines, thereby accelerating insulin resistance and type 2 diabetes (T2D). This review synthesizes current 
evidence on thermogenic fat in human and experimental obesity and its role in diabetes progression. We outline 
developmental and functional differences between classical brown and beige adipocytes, then examine how 
obesity disrupts sympathetic innervation, adrenergic signaling, mitochondrial integrity, and cellular 
composition within thermogenic depots. We next discuss how loss of thermogenic and endocrine functions of 
BAT/beige fat worsens hepatic steatosis, muscle insulin resistance, β-cell stress, and cardiovascular risk. 
Finally, we review lifestyle, surgical, and pharmacologic interventions that restore or substitute thermogenic 
activity and highlight key questions for translating BAT/beige biology into durable therapies for obesity-driven 
diabetes.