I wrote last week about the amazing benefits of dietary fiber. But what is fiber? It comes in numerous forms. In this entry, we’ll look at what type of fiber to eat, how much to have, and how to make it enjoyable and doable.
“Fiber” is a catchall term for various kinds of plant matter. A common definition is this one from the Linus Pauling Institute: “Dietary fiber is a diverse group of compounds, including lignin and complex carbohydrates, which cannot be digested by human enzymes in the small intestine.”
Because they’re not digested, they pass through into the large intestine. There they are colonized by bacteria and turned into short-chain fatty acids or SCFAs, which have wonderful effects on blood glucose, cholesterol, and the immune system.
Scientists have classified fibers in several ways. One common classification is soluble versus insoluble. According to Amy Campbell, soluble fiber is the kind that turns into a gel in the intestines and slows down digestion. I think of it as being like cooked squash: a nice, soothing mush.
Insoluble fiber doesn’t break down as much. It’s in things like carrots and oat bran. It helps to speed the passage of food through the digestive system and adds bulk to stool.
If you’re dealing with inflammatory bowel or irritable bowel, you want to maximize soluble and decrease insoluble fibers. But from a diabetes angle, it doesn’t make much difference, because nearly all plant foods include both types, and both are good.
Other terms used for soluble fibers are “viscous” and “fermentable.” All these terms are similar. They mean bacteria in the colon can ferment the fiber, and that’s what we want. For the most part we can ignore these distinctions.
The Institute of Medicine also classes fibers as “dietary” and “functional.” Dietary (or “intact”) fibers come from actual plant foods. Functional (or “isolated”) fibers are extracted in some industrial process and added to foods. According to Amy Campbell, both types can help, but only dietary fibers have been shown to lower cholesterol.
So the bottom line is that eating almost any whole plant will get you a mix of good fibers. But things like starchy apples or potatoes may have too many digestible carbs, which can outweigh the fiber benefits.
How much do we need?
The Institute of Medicine says an adequate intake (AI) of fiber is 38 grams a day for men who are 14 through 50 years old and 30 grams a day for men who are above 50. For women, the AI is 25 grams for those 19 through 50 and 21 grams for those above 50. Other recommendations, including those of the US Department of Agriculture and the American Diabetes Association, call for 14 grams of fiber per 1,000 calories of food eaten, which comes out to about the same thing.
Twenty-eight grams equals roughly one ounce, which is not much. Still, it’s twice what the average American eats, which is about 15 grams a day.
Others say you should eat more than the Institute of Medicine recommends. I say eat much more. Some researchers recommend 25–50 grams of fiber a day. I say shoot for 50, or as high as you can get.
If you wanted to eat 50 grams of fiber a day, could you? To reach such numbers (which our ancestors ate routinely, and which our bodies have evolved to eat), you will have to eat really high-fiber foods.
Wikipedia has a chart of food categories here, which shows that beans and dark green vegetables have super-high fiber content (6.4 grams per serving for dark green vegetables and 8.0 grams per serving for beans.) Truly whole grains average 2.4 grams per serving. But you have to be careful that the grains are really whole, as many foods that contain whole grain also contain refined grain.
Nutritionists say read labels carefully to find out the fiber content. That’s true for grain products, but I prefer the products that don’t have labels, such as beans, fruits, and vegetables. Nuts and seeds are also good sources of fiber and healthy in other ways, too.
Things to remember
For some people, soluble fiber may be too close to plain old starchy carbs. It seems to raise their after-meal glucose levels. But this may be a question of how the food is prepared.
Where digestible carbs end and fiber starts is not always clear. With foods like sweet potatoes, baking turns most of the fiber into a carbohydrate with a glycemic index close to that of sugar. But boiled sweet potatoes have less glycemic effect. The only way to know how different high-fiber foods affect your blood glucose is to monitor your levels after eating them.
Also be sure to drink water when eating fiber-rich foods. Fiber pulls water out of your colon, so you need to drink more liquids to compensate. I have become dehydrated from eating lots of fiber without drinking fluids. A more likely situation is that you’ll get constipated if you don’t drink water. Doctors recommend 13 cups of fluid a day for men and 9 cups for women, with more if you’re going high-fiber.
A good way to prepare fiber is to make a smoothie. Just rip up a bunch of leaves of kale or some other vegetable, chop up some beets or fruit, maybe some grapes, pour in some carrot juice, almond milk, milk, or water, and blend for 30 seconds or so. Add whatever you want (for example, ginger, cinnamon, or whatever) for flavor.
If you do carb counting, you should include the carbs in high-fiber foods such as beans or whole-grain foods. You might want to monitor occasionally as you try food high in soluble fiber to make sure it doesn’t raise your blood glucose.
One hundred trillion bacteria are in your gut right now, waiting for some fiber they can change into healthy SCFAs to help your diabetes and protect your heart. Please feed them!