Thermogenic adipose tissue in older adults with obesity: a narrative review of mechanisms, brown fat resistance, and the translational relevance of exercise and nutrition

Population aging is accelerating, and obesity is becoming more common in older adults, creating a growing clinical burden. Brown adipose tissue (BAT), together with inducible beige adipocytes in white fat depots, supports adaptive thermogenesis through substrate oxidation and helps clear glucose and lipids from the circulation. Aging and obesity often coexist, reducing BAT volume and activity while lowering the browning capacity of white adipose tissue. Thermogenic responsiveness to cold exposure, exercise, and diet-related signals appears attenuated in this context. This pattern is often described as brown fat resistance. In real-life settings, it may make older adults' responses to lifestyle interventions less consistent and less pronounced. This narrative review synthesizes evidence from animal models and human studies to delineate the principal mechanisms by which exercise and nutrition shape BAT and beige adipose biology. Relevant English-language articles published up to December 2025 were identified through PubMed, Scopus, and Web of Science, and screened according to their topical and methodological relevance. We also examine how age-related limits, including sarcopenia, chronic low-grade inflammation, weaker sympathetic and β-adrenergic signaling, and endocrine imbalance, raise the activation threshold and reduce thermogenic responses. Much mechanistic evidence comes from rodent studies or young, metabolically healthy populations, whereas human findings in obese older adults remain heterogeneous because of differences in endpoints, cold-stimulation protocols, phenotype characterization, and small sample sizes. Based on this evidence, we outline an integrated framework that links structured exercise with thermogenesis-supportive nutrition, while cautioning against overinterpretation of surrogate imaging readouts. The aim is to make thermogenic adipose activation more feasible in obese older adults by improving whole-body metabolic conditions and substrate handling, strengthening inter-organ communication, and increasing adipose tissue sensitivity to external triggers. We also highlight the need for future trials to use clear prespecified stratification suitable for older adults, and to establish standard safety checks and monitoring plans that support practical and individualized strategies targeting BAT and beige adipose tissue.