Solving the Fiber Puzzle

Last week we had an old friend over for the weekend. She has irritable bowel syndrome (IBS). IBS gives her severe abdominal pain, diarrhea, and/or constipation. So she wouldn’t get sick, I brushed up on dietary recommendations for people with IBS. I learned a lot about fiber, and it turned out to be highly relevant for diabetes.

The American Diabetes Association has guidelines on fiber, but they turn out to be probably too low and incomplete. They recommend 25–50 grams of fiber a day, an improvement over their old recommendation of 24 grams per day. Twenty-five grams a day is more than the 14–15 grams the average American eats daily, but it’s not enough.

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And it’s not just how much fiber, but what kind. The two main categories of fiber are “soluble” and “insoluble.” Soluble fiber dissolves in water and makes a thick gel that moves smoothly through your intestines. It soothes your bowel and helps it function better. It slows down stomach emptying time, so it reduces after-meal glucose spikes. It’s good for glucose levels, cholesterol levels, and keeps your bowel from being irritated.

Soluble fiber is found in what are often called “starches,” like rice and pasta, and in root vegetables like potatoes, yams, and beets. It’s also in tropical fruits like bananas and papayas.

Insoluble fiber is what most people think of as fiber. Lettuce leaves, fruit skins, raw carrots. Things you have to crunch. It prevents constipation and keeps the acid/base balance of the bowel where it should be. It can also be very irritating to the bowel, especially if you have IBS.

The average American eats roughly two thirds of his fiber in insoluble form. But some studies show that much higher levels of soluble fiber are key for improving glucose and cholesterol numbers.

A series of studies by doctors in Texas documented that 50 grams of fiber a day, equally divided between soluble and insoluble, “improves glycemic control, decreases hyperinsulinemia [excess insulin], and lowers plasma lipid [fat and cholesterol] concentrations in patients with type 2 diabetes.”

You don’t want to and can’t really get too strict about soluble versus insoluble fibers, because many foods contain both. As Amy Campbell wrote in a blog entry earlier this year, leading sources of fiber are oats and oat bran, beans and peas, fruits, and vegetables. All these foods contain soluble as well as insoluble fiber. Most fruits and whole grains are insoluble on the outside and soluble on the inside. If you’ve got digestive problems, or maybe even if you don’t, start meals with the soothing soluble fibers like yams or bananas. That gets your intestines ready. Then move onto the insoluble stuff.

But Doesn’t High-Fiber = High-Carbohydrate?
Yes and no. All fiber is carbohydrate, but a lot of it doesn’t get into your system, because it just passes through without being absorbed. However, all fiber comes from plants, so it comes along with other carbohydrates that are absorbed into your system. (You can take pure fiber, no-calorie supplements, but you will need a lot of them to replace the fiber you can get in food.)

You can eat fiber-containing foods that are relatively low-glycemic-index, such as brown rice, oatmeal, or buckwheat (soba) noodles, plus some root vegetables.

The Web site Help for IBS includes squash, turnips, applesauce, avocados, soy, tortillas, mushrooms, mangoes, and many other foods on their soluble fiber list. You can see the whole list here.

I wouldn’t mind getting most of my calories from this list. In fact, I probably do, but I don’t have diabetes. If this kind of eating is new to you, you may want to check its effect on your diabetes control for yourself by monitoring your blood glucose to see how these foods affect you.

The thing I really like about this soluble fiber is that it feels good inside you. It reminds me of the Chinese medicine prescription for food — everything cooked, soft is good, warm is good. I guess it’s kind of older people’s food. It’s easy on your gut. Twenty years ago, I might have scoffed at all this mush, but maybe starting younger would have had advantages. To make foods containing soluble fiber taste good, try eating them with various spices like cinnamon, ginger, curry powder, or anything you like.

One warning — fiber does no good if you don’t drink enough fluids. Fiber combines with water to fill you up and improve your gut function. Without the fluids, you’ll wind up constipated and miserable.

Make sense to you? How much soluble fiber do you consume? Do you notice that fiber makes a difference for you? I’m really interested in this, because the super-low-carbohydrate approach typically translates into high meat consumption. And meat farming is usually cruel to animals and unsustainable for the environment. So I’m drawn to this soluble fiber idea. Let me know what you think, please.

  • Steve Parker, M.D.

    I think the soluble versus insoluble fiber concept is a little too esoteric for the general public, regardless of the potential health benefits.

    Kinda like “limit your saturated fat intake to 7% of total caloric intake,” recommended by the American Heart Association. No one actuallly does the calculation.

    Generous amounts of dietary fiber, I can get behind. But 50 g/day? Not for the general public.

    -Steve

  • CalgaryDiabetic

    I agree the soluble fiber foods are great but my meter does not like them. They skyrocket the BG as much as sugar if not more gram per gram. Rice and potatos are foods diabetes should not touch with a ten foot pole. I take maybe 15 grams of metamucil per day in two batches effect on blood glucose is tolerable.

  • sharon

    Education is the key to having good control of weight and blood sugar levels. Anything that absorbs into my system more slowly is an advantage to good blood glucose control, unless I am at the other end of the spectrum and having a low blood sugar. Fiber is also effective to help prevent diverticulitis. The more I learn the better I can take care of myself. Worth incorporating into my diet.