Fiber is good for your heart, your diabetes, and your blood pressure. But fiber is “indigestible.” It never even goes into the body beyond the gut. So how could it have all those benefits? Well, it does all that and more. Here’s the story.
To understand the benefits of fiber is to learn about the incredible human digestive system. Nothing I’ve read from doctors or nutritionists even hints at how remarkable our bodies are at handling food.
According to drmyhill.com, run by British doctor Sarah Myhill, humans are “almost unique amongst mammals,” because we have two totally different digestive systems linked together. The upper gut [stomach and small intestine] is a carnivorous gut (like a dog’s or a cat’s) to deal with meat and fat. But “the lower gut (large bowel or colon) is full of bacteria and is a fermenting, vegetarian gut (like a horse’s or cow’s) to digest vegetables and fiber.”
Think about it. Haven’t you been told the colon was just a place to accumulate waste and prepare to push it out of your body? It’s not true! A lot of nutrients are digested and absorbed from the colon. It’s just that our body doesn’t do the digesting. Bacteria do.
In the upper gut, our body makes acid, bile, and enzymes that break down carbohydrates, protein, and fat, and push them through the intestinal wall into the blood. Fiber is plant material that is too tough for our enzymes (think broccoli stems), so it stays in the gut. There it helps other food continue along down the intestine and blocks bad stuff from getting out of the gut and into the bloodstream.
But wait! Once it gets to the colon, fiber is colonized by trillions of bacteria that ferment it into usable stuff. Dr. Myhill says this supposedly “indigestible” food can produce up to 500 calories of energy per day, helping keep our bodies warm. The energy doesn’t come from glucose. Fibers don’t break down into sugars the way other carbs do. Bacteria change them into something called short-chain fatty acids, or SCFAs.
SCFAs seem to balance our systems out. Studies show they can do the following:
• Stabilize blood glucose levels by acting on pancreatic insulin release and liver control of glycogen breakdown
• Stimulate gene expression of glucose transporters
• Regulate glucose absorption from the gut
• Suppress cholesterol synthesis by the liver and reduce blood levels of LDL cholesterol and triglycerides
Notice SCFAs help insulin production and signaling and decrease insulin resistance. They work in the pancreas, the gut, and the liver. That’s basically a total diabetes medicine! Along with fiber, they also protect the colon from formation of polyps (which can lead to cancer) and increase absorption of dietary minerals. They stimulate production of T helper cells, antibodies, leukocytes, cytokines, and lymph mechanisms having crucial roles in immune protection.
Our nutritionist Amy Campbell reports that in the bowel itself, fiber — specifically, insoluble fiber — can prevent hemorrhoids and constipation, decrease exposure to toxins, and “help you feel full so you eat less.”
How this works
All SCFAs are created by “fermentation,” the same process used in turning barley into beer or grapes into wine. Could it be good to have that going on inside of us?
Yes. We’re used to thinking of bacteria as enemies. We never realize they are part of our world, both outside and inside of us, and without them, we could barely exist at all. If we have the right kind of bacteria in our guts, they can turn any plant food into butyric, acetic (our old friend vinegar), propionic, valeric, and other helpful acids — that scientific evidence is revealing to have significant health benefits.
If we don’t have the right kind of bacteria, especially a class called “bacteroides,” other bacteria and microbes, such as yeast, will move into the colon. These species produce chemicals that are unhealthy for us. The good bacteria can die from antibiotic use or because we don’t eat enough fiber.
Fiber and fermentation explains a lot. It explains why a vegan diet can be good for some (probably not all) people with diabetes, even though it’s mostly carbs. Vegan diets have lots of fiber. (All fiber comes from plants. Meat, no matter how tough, doesn’t have any.)
It explains why vinegar is good for you. It’s a natural SCFA that we may not get enough of, because we don’t eat enough fiber.
Amy Campbell wrote here about a study where vegan eaters improved more than standard ADA–style eaters, even though “the vegan group wasn’t limited in their calories, carbohydrates, or portions.” How is this possible? It’s got to be the fiber.
I’m not saying fiber is a miracle cure. In the studies, high-fiber usually led to about 20% improvements in glucose and cholesterol. But it’s clearly good for you. Maybe higher levels for longer would have led to greater improvement.
Well, I’m over my word limit, and I realize I haven’t even talked about what fiber is, how much to eat, or how to get it. We’ll get to that next week.