As I explained in my last video, when our blood volume drops, our kidneys detected in angiotensin is released.

When our blood volume rises, on the other hand, our heart detects it and releases a hormone

called ANP, atrial-natriuretic peptide,

also known as ANF, atrial-natesyretic factor.

We used to think our heart was just a pump, but now we know it's also a gland.

There are stretch receptors in the first chamber of our heart, and when extra blood

pours into the heart,

A&P is released. What does it do? As the title of review in a obesity journal put it,

heart hormones fuel a fire in fat. If you drip A&P on human fat muscle tissue, fat is rapidly

released and the muscle cells

ramp up their capacity to burn it. Infuse A&P into people, and the rate at which fat is mobilized

and burned can shoot up 15%. You can take muscle biopsies from people and show how much better

their muscles get at burning fat in the presence of elevated A&P levels.

No surprise then that obese and overweight individuals tend to have considerably lower levels

in their bloodstream, so the way to a person's stomach may be through their heart.

Why would this stretch-sensitive heart hormone tap into our fat stores? Well, when does the heart get stretched during intense physical activity?

We used to think it was just the adrenaline-type hormones that are released when you exercise,

that mobilize fat from our tissues, but now we know that ANP from our heart plays a key role as well.

Inject people with the amount of ANP they'd normally get in their system when exercising, and their whole body fat burning goes

up, even if they're just sitting on the couch. How else can we stretch our heart that extra

little bit to release AMP? By increasing our blood volume by drinking extra water.

When you don't drink for 12 hours straight, your AMP levels in your blood fall by about 25

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