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Your digestive system impacts the rest of your body in all sorts of unexpected ways, from keeping your heart healthy to literally making you feel happier.

Thanks to Metamucil for sponsoring this episode of SciShow! Visit and sign up for the Metamucil Two-Week Challenge to see how a healthy digestive system may help to improve your overall health and happiness!

Hosted by: Hank Green

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This episode of SciShow is sponsored by Metamucil. [ ♪ Intro ].

If you follow me on my other YouTube channels or on Twitter, you might know that I’m a huge fan of a healthy digestive system. And there’s more science behind that than you might think.

Your digestive system impacts the rest of your body in all sorts of unexpected ways, from keeping your heart healthy to literally making you feel happier. It might seem like your digestive system is just there to process all the stuff you put in your mouth and expel anything you can’t recycle into something useful. And it is.

But in performing this essential waste management service, it affects basically every other part of your body. For example, when you break down your meals into useful chunks, it’s your blood that moves those nutrients to the tissues that need them. And that’s why what you eat or drink and the health of your digestive system can affect the level of cholesterol in your blood, which in turn impacts the health of your heart.

Cholesterol is an umbrella term for a particular group of waxy fats, and it’s not inherently terrible for you. But if there’s too much of it in your blood, the cholesterol can stick to the walls of your blood vessels and form plaques, the first step toward heart disease. Counterintuitively, your blood cholesterol doesn’t directly correlate with how much of the stuff you eat.

It’s really more about how well your digestive system is working and what other things you eat at the same time. That’s because your body uses cholesterol to make bile, the digestive juice secreted into your intestines from your gallbladder. In fact, when digesting your meal, more of the cholesterol in your intestines is from bile than from the food you just ate.

And eating certain kinds of foods can reduce the amount of that cholesterol you reabsorb, lowering the total amount of it in your blood. Like eating enough fiber, for example. Fiber is a really big category of stuff that basically includes all the carbohydrates your body doesn’t digest easily.

It can be soluble, meaning it dissolves in water, or insoluble, meaning it doesn’t dissolve. And a few kinds of soluble fibers also form a gel. Both insoluble and soluble gelling fiber will add bulk to your feces and help make your poops more regular.

But gelling soluble fibers in particular increase their moisture content, making them move more easily through, and out, of your digestive system. And they’re the ones that really help lower your blood cholesterol, too. One of the most effective viscous soluble fibers seems to be found in psyllium husk, which is made up of the seed coats from a plant.

Clinical trials have found that adding psyllium husk to your diet can help lower your bad cholesterol levels by 6-24%, and that’s probably because its soluble fiber literally binds with cholesterol in your intestines, dragging the stuff with it as it’s excreted. Fiber might also help boost levels of good gut bacteria, which can affect what nutrients you absorb from your meals. In fact, lots of foods affect the little critters living inside of you, and that’s a big part of why what you eat can have a big impact on your immune system.

Even though your intestines are inside your body, they’re still exposed to the outside world, and that puts them on the front lines of the war between you and all the nasty things that want to infect you. That’s why more than half of your immune cells actually live in your digestive system. And, luckily, you also have a hired army of foot soldiers there fighting on your side: your gut microbiome.

Your gut bacteria can protect you from intestinal pathogens like E. coli and Giardia by out-competing them or straight-up killing them. But studies also suggest that a healthy microbiome can help with all sorts of infections, including ones that never come near the gut. The right microbes in your intestines can reduce your likelihood of developing a respiratory infection, for example.

Researchers think that’s because those microbes stimulate the immune cells in your intestines, which then communicate with the cells in your respiratory system. We still have a lot to learn about the specifics of how what you eat changes what lives in your bowels, but we do know that it can have a marked impact on your gut microbiome. So small changes to your diet and the health of your digestive system can really boost or weaken your immune system.

Your gut health can also be an important factor in your mental health. Obviously, you need to make sure you have enough nutrients to keep your brain tissue healthy, but the impact of your bowels on your brain goes beyond that. You actually have a second brain of sorts, called your enteric nervous system, that coordinates your digestion.

More than 100 million nerves have to work together to ensure everything from chewing to pooping runs smoothly. And this ‘brain in your gut’ communicates with the brain in your head to help regulate mood and anxiety. We’ve known for a long time that disorders that upset your stomach can really mess with your mental health, with strong links to things like depression and anxiety disorders.

And not just in the generic, like, I-don’t-feel-well kind of way. The health of your gut and its microbes influence the messages sent to your brain via the vagus nerve, which can alter all kinds of levels of key proteins and neurotransmitters. We have a lot more to learn to fully understand the connection between what you eat, what happens in your digestive system, and how that affects the rest of your body.

But one thing is for sure, a happier and healthier gut makes for a happier and healthier you. And that’s something that Metamucil has really helped me with. It’s a supplement made up of psyllium husk, that gelling soluble fiber I was talking about earlier.

The fiber in Metamucil can help your bowels keep things moving if you’re feeling constipated, or slow things down and make your poop thicker if you’re on the… the other end of that spectrum. And even before it gets all deep in your intestines, it can help you feel fuller. Overall, it makes your bowel movements easier and more regular, less straining and struggling, and sitting in the bathroom for 20 minutes while you wait for things to get a move on and get all stressed out looking at twitter.

And I can say for certain that having more regular, softer poops has made me a much happier person and I think it might make your life a lot better, too. [ ♪ Outro ].