Human: The World Within

-The fact that a lack of fuel might make you healthier isn't the only irony lurking in the gut. It's also home to a giant population of bacteria... ...that, instead of making you sick, might actually be the key to a strong immune system. See, despite being in the middle of our body, the gut is our most direct connection to the outside world. Food brings with it pieces of nature, and nature makes itself at home inside us. There's a symbiotic relationship between our own cells and foreign ones, an alien universe that runs right through us. -The microbiome essentially describes the bacteria living in our gut. Scientists estimate we have over 10 trillion bacteria in our gut, which are playing a great role. They help us break down food, reabsorb nutrients and vitamins, and even play a really critical role in keeping out the bad bacteria. -The gut is a diverse environment where our own cells, food from outside, and the bacteria that live within us all coexist. And because bacteria and human cells are constantly touching, it's a perfect place for the body to learn what's safe... ...and what's dangerous. -Where is your immune system? It's in your gut. -The thin mucus barrier that protects the gut is home to 80% of all the immune cells in the body. As we digest, these cells learn to tell the difference between friend and foe. They know that what we eat is fuel, even though it comes from the outside. And anything that can hurt us provokes a response. -An intact intestinal membrane is really essential for protecting us from toxins and keeping us healthy. -But when these cells malfunction, fuel can suddenly become poison.