One of the health recommendations most Americans fall short on is fiber consumption. Fiber is the indigestible component of foods, one that passes through your digestive tract without being absorbed. Although fiber itself offers no nutritional value, whole foods that are naturally high in fiber are among the most nutritious. Plus, research shows fiber has a number of health benefits.
As with many dietary components, more isn’t always better. Is it possible to consume TOO much fiber?
The Health Benefits of Fibers: Fiber Comes in Different Varieties
Researchers divide fiber into two main types: soluble fiber and insoluble fiber. Soluble fiber dissolves in water and inside the dark, moist recesses of the digestive tract form a thick gel that slows down digestion. Because soluble fiber delays digestion, you break down carbohydrates more slowly in the presence of fiber. This means your blood sugar rises less quickly after a meal.
Soluble fiber is the form linked with heart health because it has a modest cholesterol-lowering effect. Plus, a diet high in soluble fiber helps with weight loss by increasing satiety. When your digestion slows in the presence of fiber, you feel full faster.
In contrast to soluble fiber, insoluble fiber does not dissolve in water. Instead, it bulks up your stool and draws in water. By doing so, it helps waste move more quickly out of your body. As you might anticipate, insoluble fiber is most effective for relieving constipation and making bowel habits regular.
You can also classify fiber as “fermentable” and “non-fermentable.” This refers to whether bacteria in your intestines can digest a fiber. If they can, it’s fermentable. Fiber that’s fermentable has unique health benefits that non-fermentable fiber doesn’t.
What kind of benefits? When bacteria break down non-digestible carbohydrates or fiber, they produce by-products called short-chain fatty acids that are beneficial for colon health. Preliminary research suggests these fatty acids may protect against colon cancer.
Which Foods Are High in Which Types of Fiber?
Many fruits and vegetables contain soluble fiber. If you eat the peels and skin, you’re also getting a healthy dose of insoluble fiber, the kind that doesn’t dissolve. You also find insoluble fiber in the bran portion of whole grain foods.
Other good sources of soluble fiber include nuts, beans, flaxseed, lentils, and oats. Fermentable fiber is called resistant starch, referring to the fact that the human digestive tract can’t break it down but gut bacteria can.
Fermentable Fiber and Resistant Starch
Resistant starch appears to have some of the same health benefits as soluble fiber. This form of fermentable fiber is present in all carbohydrate-containing foods but the quantity varies with how the food is stored, cooked, and processed.
Foods that are naturally high in resistant starch include seeds, whole grains, beans, lentils, green bananas, and raw potatoes. One way to increase the amount of resistant starch content in potatoes is to refrigerate them for 12 hours after cooking but before eating.
Food manufacturers also make their own forms of fiber and resistant starch that they add to products like cereals and nutrition bars. These types are referred to as “functional fiber” because they’re extracted from food sources and added back into products to give them more fiber. One advantage of adding functional fiber to a product is it gives the product texture without adding additional calories. Examples of functional fiber include resistant dextrins, fructooligosaccharides, and psyllium husks.
What’s so special about resistant starch? Gut bacteria produce short-chain fatty acids when they ferment resistant starch, giving this form of fermentable fiber unique health benefits. As mentioned, short-chain fatty acids help keep the lining of the colon healthy by lowering its pH. In addition, research show these fatty acids help reduce inflammation inside the colon and may improve the symptoms of some bowel problems like inflammatory bowel disease. Like soluble fiber, resistant starch makes you feel full more quickly and helps with blood sugar control by improving insulin sensitivity.
Can You Get Too Much Dietary Fiber?
So, what’s the scoop on getting too much fiber? For most people, overdosing on fiber isn’t a concern. The USDA recommends that adults take in 14 grams of fiber for every 1,000 calories consumed. For adults, that’s around 25 to 35 grams of fiber. The amount the average American takes in is pretty low – about 15 grams a day. So, we aren’t even meeting our fiber recommendations, much less getting too much.
How can getting too much fiber be a problem? For one, it can cause intestinal upset, especially if you introduce more into your diet too quickly. Another concern is that consuming too much fiber could interfere with mineral absorption, including calcium, zinc, and iron. Fiber contains compounds called phytates that form complexes with minerals, making them difficult to absorb. For the average person, this isn’t a concern. Unless you consume large amounts of supplemental fiber, you should have no problem with mineral malabsorption. The bigger problem for most folks is a lack of fiber.
In fact, one form of fiber, resistant starch, may actually help you absorb minerals such as magnesium, zinc, and iron, based on research. Plus, don’t forget that fiber-rich whole foods, including fruits, vegetables, and whole grains, are a good source of minerals anyway.
On the other hand, some people are sensitive to certain forms of fiber, especially fructooligosaccharides. If that’s the case, you might experience bloating, cramping or diarrhea when you consume foods that contain this form of fiber. One way to find out if you’re sensitive is to remove foods that contain fructooligosaccharides from your diet and see if your symptoms improve.
Get Your Fiber from Whole Foods
Fiber is least likely to be a problem, on your digestive tract or mineral absorption, if you get your fiber from whole foods. If you use fiber supplements and functional fibers, you could experience more side effects such as digestive upset although even then you can avoid them by introducing added fiber slowly into your diet. As with any abrupt change in diet, your body needs a chance to adjust to dietary changes, even positive ones.
References:
Crit Rev Food Sci Nutr. 1991;30(1):1-22.
J. Nutr. January 1, 2003.vol. 133 no. 1 1-4.
Nutrition Bulletin. Volume 30, Issue 1, pages 27-54, March 2005.
Today’s Dietitian. Vol. 14 No. 4 P. 40. April 2012.
Am J Clin Nutr. 2010 Apr;91(4):932-9. doi: 10.3945/ajcn.2009.28443. Epub 2010 Feb 17.
Nutr Res. 2009 Feb;29(2):100-5. doi: 10.1016/j.nutres.2009.01.004.
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