Let’s admit it. Few of us like to think, much less talk about our colons. But you might be surprised at the importance of what gets into your colon and what goes on inside it. This little-loved part of our bodies is actually less an onboard garbage can and more like the unlikeliest medicine chest.
There is abundant medical evidence that diet greatly influences health, and new science is showing us why this is so. It is also showing us that advocates of trendy paleo and vegan diets are missing the big picture of how our omnivorous digestive system works.
Your colon is the home for much of your microbiome—the community of microbial life that lives on and in you. In a nutshell, for better and worse, what you eat feeds your microbiome. And what they make from what you eat can help keep you healthy or foster chronic disease.
To gain an appreciation of the human colon and the role of microbes in the digestive tract as a whole, it helps to follow the metabolic fate of a meal. But, first, a word about terms. We’ll refer to the digestive tract as the stomach, small intestine, and colon. While the colon is indeed called the “large intestine,” this is a misnomer of sorts. It is no more a large version of the small intestine than a snake is a large earthworm.
The stomach might better be called a dissolver, the small intestine an absorber, and the colon a transformer. These distinct functions help explain why microbial communities of the stomach, small intestine, and colon are as different from one another as a river and a forest. Just as physical conditions like temperature, moisture, and sun strongly influence the plant and animal communities that one sees on a hike from a mountain peak to the valley below, the same holds true along the length of the digestive tract.
Imagine you are at a Fourth of July barbecue. You saunter over to the grill to take a look at the fare. The pork ribs look great so you spear a few and add a heap of homemade sauerkraut on the side. You grab a handful of corn chips and a few pieces of celery. The vegetable skewers look good too, so you add one to the pile on your plate. And what would the Fourth of July be without macaroni salad and pie?
You lift a rib to your mouth and start gnawing. A forkful of sauerkraut mingles well with the meat and you crunch your way through another mouthful. The macaroni squishes between your teeth, but the celery takes some chewing. It all slips down the hatch and lands in the acid vat of your stomach where gastric acids start dissolving the bits of food. On the pH scale, where 7 is neutral and lower values are more acidic, the stomach is impressive. Its acidity ranges from 1 to 3. Lemon juice and white vinegar are about a 2.
After the stomach acids work over your meal, the resultant slurry drops into the top of the small intestine. Right away bile from the liver shoots in and starts working over the fats, breaking them down. Pancreatic juices also squirt into the small intestine to join the digestive party. Your Fourth of July feast is now on its way to full deconstruction into the basic types of molecules—simple and complex carbohydrates (sugars), fats, and proteins. In general, there is an inverse relationship between the size and complexity of these molecules and their fate in the digestive tract. Smaller molecules, primarily the simple sugars that compose the refined carbohydrates in the macaroni, pie crust, and chips are absorbed relatively quickly. Larger or more complex molecules take longer to break down and are absorbed in the lower reaches of the small intestine.
The sausage-like loops of the small intestine provide an entirely different type of habitat for your microbiota than the stomach. Acidity drops off rapidly and, in combination with all the nutrients, the abundance of bacteria shoots up to 10,000 times more than that in the stomach. But conditions still aren’t ideal for bacteria in the small intestine. It’s too much like a flooding river. And understandably so, considering that about seven quarts of bodily fluids, consisting of saliva, gastric and pancreatic juices, bile, and intestinal mucus flow through it every day. And that’s not including the two additional quarts of whatever other liquids you consume. The rushing swirl of fluids entrains food molecules and bacteria and carries them rapidly downstream. The constant motion means that nothing stays put for long, so bacteria can’t really settle in and contribute much to digestion.
By the middle to lower reaches of your small intestine, the fats, proteins, and some of the carbohydrates in the Fourth of July slurry are sufficiently broken down for absorption and pass into the bloodstream through the intestinal wall. Notice we said some of the carbohydrates. A good amount of them aren’t broken down at all. These complex carbohydrates, what your doctor calls fiber, have a completely different fate than simple carbohydrates.
They drop, undigested, into the slough-like environment of the colon. With a neutral pH of about 7, the colon is a paradise for bacteria compared to the acid vat of the stomach or the churning rapids of the small intestine, where the pH is slightly lower.
Deep within the safety of our inner sanctum, communities of microbial alchemists use our colon as a transformative cauldron in which to ferment the fiber-rich complex carbohydrates we can’t digest. But it takes the right microbes. For example, Bacteroides thetaiotaomicron makes over 260 enzymes that break apart complex carbohydrates. In contrast, the human genome codes for a paltry number. We can only make about 20 enzymes to break down complex carbohydrates.
by David R. Montgomery and Anne Biklé, Nautilus | Read more:
Image: Courtesy of the authors
There is abundant medical evidence that diet greatly influences health, and new science is showing us why this is so. It is also showing us that advocates of trendy paleo and vegan diets are missing the big picture of how our omnivorous digestive system works.
Your colon is the home for much of your microbiome—the community of microbial life that lives on and in you. In a nutshell, for better and worse, what you eat feeds your microbiome. And what they make from what you eat can help keep you healthy or foster chronic disease.
To gain an appreciation of the human colon and the role of microbes in the digestive tract as a whole, it helps to follow the metabolic fate of a meal. But, first, a word about terms. We’ll refer to the digestive tract as the stomach, small intestine, and colon. While the colon is indeed called the “large intestine,” this is a misnomer of sorts. It is no more a large version of the small intestine than a snake is a large earthworm.The stomach might better be called a dissolver, the small intestine an absorber, and the colon a transformer. These distinct functions help explain why microbial communities of the stomach, small intestine, and colon are as different from one another as a river and a forest. Just as physical conditions like temperature, moisture, and sun strongly influence the plant and animal communities that one sees on a hike from a mountain peak to the valley below, the same holds true along the length of the digestive tract.
Imagine you are at a Fourth of July barbecue. You saunter over to the grill to take a look at the fare. The pork ribs look great so you spear a few and add a heap of homemade sauerkraut on the side. You grab a handful of corn chips and a few pieces of celery. The vegetable skewers look good too, so you add one to the pile on your plate. And what would the Fourth of July be without macaroni salad and pie?
You lift a rib to your mouth and start gnawing. A forkful of sauerkraut mingles well with the meat and you crunch your way through another mouthful. The macaroni squishes between your teeth, but the celery takes some chewing. It all slips down the hatch and lands in the acid vat of your stomach where gastric acids start dissolving the bits of food. On the pH scale, where 7 is neutral and lower values are more acidic, the stomach is impressive. Its acidity ranges from 1 to 3. Lemon juice and white vinegar are about a 2.
After the stomach acids work over your meal, the resultant slurry drops into the top of the small intestine. Right away bile from the liver shoots in and starts working over the fats, breaking them down. Pancreatic juices also squirt into the small intestine to join the digestive party. Your Fourth of July feast is now on its way to full deconstruction into the basic types of molecules—simple and complex carbohydrates (sugars), fats, and proteins. In general, there is an inverse relationship between the size and complexity of these molecules and their fate in the digestive tract. Smaller molecules, primarily the simple sugars that compose the refined carbohydrates in the macaroni, pie crust, and chips are absorbed relatively quickly. Larger or more complex molecules take longer to break down and are absorbed in the lower reaches of the small intestine.
The sausage-like loops of the small intestine provide an entirely different type of habitat for your microbiota than the stomach. Acidity drops off rapidly and, in combination with all the nutrients, the abundance of bacteria shoots up to 10,000 times more than that in the stomach. But conditions still aren’t ideal for bacteria in the small intestine. It’s too much like a flooding river. And understandably so, considering that about seven quarts of bodily fluids, consisting of saliva, gastric and pancreatic juices, bile, and intestinal mucus flow through it every day. And that’s not including the two additional quarts of whatever other liquids you consume. The rushing swirl of fluids entrains food molecules and bacteria and carries them rapidly downstream. The constant motion means that nothing stays put for long, so bacteria can’t really settle in and contribute much to digestion.
By the middle to lower reaches of your small intestine, the fats, proteins, and some of the carbohydrates in the Fourth of July slurry are sufficiently broken down for absorption and pass into the bloodstream through the intestinal wall. Notice we said some of the carbohydrates. A good amount of them aren’t broken down at all. These complex carbohydrates, what your doctor calls fiber, have a completely different fate than simple carbohydrates.
They drop, undigested, into the slough-like environment of the colon. With a neutral pH of about 7, the colon is a paradise for bacteria compared to the acid vat of the stomach or the churning rapids of the small intestine, where the pH is slightly lower.
Deep within the safety of our inner sanctum, communities of microbial alchemists use our colon as a transformative cauldron in which to ferment the fiber-rich complex carbohydrates we can’t digest. But it takes the right microbes. For example, Bacteroides thetaiotaomicron makes over 260 enzymes that break apart complex carbohydrates. In contrast, the human genome codes for a paltry number. We can only make about 20 enzymes to break down complex carbohydrates.
by David R. Montgomery and Anne Biklé, Nautilus | Read more:
Image: Courtesy of the authors
