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Answer by Tirumalai Kamala, Immunologist, Ph.D., Mycobacteriology:
From 3 Recent mouse model research (4) even added a third fat flavor, beige/‘brite’, which is induced ‘brown in white’ fat.How ambient temperature, fat and energy expenditure intersect How are energy expenditure and fat type related? Simply put, WAT stores energy, BAT spends it. How does BAT do this? BAT adipocytes (fat cells) express a unique gene, SLC25A7, which encodes the mitochondrial uncoupling protein 1 (UCP1) (5). ‘Embedded in the inner mitochondrial membrane, UCP1 acts as a proton conduit from the inter-membrane space to the mitochondrial matrix. Activation of UCP1 leads to the energy generated by the electron transport chain and stored in the pH and electrochemical gradient across the inner mitochondrial membrane to be dissipated as heat, rather than used to fuel ATP generation by ATP-synthase’ (6). Thus, BAT converts lipid-derived chemical energy into heat (thermal energy).
More from Quora: What are the top running technique suggestions? | Can anyone learn to enjoy running? Till recently, we thought that BAT depots were only physiologically relevant in small mammals and human infants (7, 8), even though we knew for decades that adult humans also have BAT (7). That is, until a 2009 study (9). This study showed that
BAT activity was present in 23 of 24 healthy adult men. But only when they were exposed to cold temperature. Even overweight and obese men have BAT, though significantly lower in activity compared to lean men.
Adult humans have metabolically active BAT. Obese and older people have less metabolically active BAT. BAT activity negatively correlates with BMI (Body Mass Index), i. e. higher BAT activity, lower BMI.
It’s highly innervated and vascularized (19). Its metabolic activity is partly controlled by norepinephrine secretion by the sympathetic nervous system (SNS) (20). Actually, adult human BAT is likely more accurately beige/brite (21, 22). A genetic association study found a UCP1 promoter polymorphism that reduces its expression and is associated with a higher BMI and abdominal obesity (23).
Thus, BAT could be a target for obesity treatment.Summary of human BAT studies* * Caveat to human active BAT studies: Only 18F-fluorodeoxyglucose PET-CT (positron emission tomography with computed tomography) (FDG PET-CT) unequivocally identifies human adult active BAT. Most commonly used routinely in cancer diagnostics for cancer staging, such scans use ionizing radiation, and are not possible to use in large numbers of healthy human adults. Thus, most data on active human BAT is from cancer staging studies.
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