Different triggers, one converging target
Brown and beige fat differ from ordinary white fat because they are rich in mitochondria and can dissipate energy as heat rather than store it. The molecular hub for this is UCP1, a protein that uncouples the mitochondrial proton gradient from ATP production so the energy is released as warmth. Several distinct stimuli converge on increasing UCP1 activity or abundance: cold exposure acting through the sympathetic nervous system, dietary compounds like capsaicin, certain beta-3 adrenergic signals, and exercise-related signaling. The diagram groups these because they reach a shared endpoint by different routes.
Cold is the most reliably effective and best-studied trigger in humans; the others vary more in how strongly they engage this pathway.
What activation does and does not promise
Activating brown fat increases energy expenditure, which is why it draws interest for weight management. The realistic picture is more modest: adult humans carry limited amounts of brown fat, its mass and responsiveness differ between people, and the additional calories burned are usually small relative to overall energy balance. Much of the strongest evidence for big effects comes from animal models rather than humans.
This is general educational information about a pathway, not medical or weight-loss advice. No supplement reliably converts brown fat activation into meaningful fat loss on its own, so consult a qualified professional before relying on such claims.