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As I explained in my last video, when our blood volume drops, our kidneys detect it and 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 natriuretic 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, ANP is released. What does it do? As the title of a review in an obesity journal put it: “Heart hormones fueling a fire in fat.”
If you drip ANP on human fat and muscle tissue, fat is rapidly released, and the muscle cells ramp up their capacity to burn it. Infuse ANP into people, and the rate at which fat is mobilized and burned can shoot up by 15 percent. You can take muscle biopsies from people and show how much better their muscles get at burning fat in the presence of elevated ANP levels. It’s 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 we exercise that mobilized 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 ANP? By increasing our blood volume by drinking extra water. When you don’t drink for 12 hours straight, your ANP levels in your blood fall by about 25 percent. But chug down about four glasses of water, and your levels can jump up by 50 percent within 90 minutes. Now that’s too much to drink at one time, but it can offer a sense of how much potential control we have over this fat-burning hormone.
How else could we trick our body into producing this exercise hormone without lacing up our gym shoes? If it’s all about pooling extra blood into our heart, what about lying with our head tilted down? It sounds kind of funny, but researchers took the possibility seriously enough to run the experiment. They laid people down at just a six-degree angle, a slight tilt. That’s like putting three or four bricks under the posts at the foot of your bed. So, it’s not like they were hanging upside down. They were almost flat, but at just enough of a slant for gravity to draw extra blood into their torso. Within an hour, their ANP levels doubled and stayed up for the four hours the experiment ran. Okay, but did they all of a sudden start burning more fat? Yes, the proportion of fat they were burning as fuel shot up by 40 percent, and they were just lying down the whole time. So, what if you tried sleeping with a slight head-down tilt by putting a few bricks under the posts of the foot of your bed? Would it cause you to burn more fat while you slept? I’ll address the potential pros and cons next.
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