A lot of cool studies about brown adipose tissue (BAT) lately; here's the rundown.
More and more, with more sophisticated techniques, scientists are discovering we have more BAT than previously believed. And they all have theories on how it works and if it can be manipulated to make us healthier.
Activated BAT secretes a lot of stuff:
Exercise increases circulating 12,13-diHOME in humans (old, young, male, female, sedentary, active) (Stanford et al., 2018).
In mice, too, and surgical removal of BAT abolishes this effect. Dosing them with 12,13-diHOME increases fatty acid uptake and oxidation in skeletal muscle.
Cold exposure induces the enzyme 12-LOX in BAT which synthesizes lipid mediators that improve glucose tolerance (Leiria et al., 2019).
Cold exposure in this #context is a few degrees above your shivering threshold. It's NOT an ice bath -- it's shorts & a t-shirt in 50(ish) degrees F (10 C).
The good news: if you dislike exercise or find cold exposure unpleasant, there are other ways, eg, beta-3 adrenergic receptor agonism and some nutrients that can be obtained via diet.
Not many good b3 options, but some of the fatty acids in seafood and dairy may help (Park et al., 2019).
And none of this works if you're stressed out. Glucocorticoids shut down BAT activity (Thuzar et al., 2018).
The bad news: even in the best case scenario, this isn't going to burn a lot of fat... but you still get metabolic improvements.
Colder might be more effective, but most studies agree that the total calorie burn is relatively miniscule (~10 kcals above baseline per hour?) -- this is not an exercise-mimetic (Sanchez-Delgado et al., 2018; Brychta et al., 2019; Fernandez-Verdejo et al., 2019; Gashi et al., 2019).
That's all for now!
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