Getting to Know Fiber… Again (Part 2)
February 7, 2011
As promised, last week the USDA unveiled the 2010 Dietary Guidelines for Americans. Unless you’re a dietitian, you’re probably not all that excited about this. And frankly, I don’t find the Dietary Guidelines all that exciting either. But they form the basis for nutrition policy in this country.
Since we’ve been talking about fiber, I was curious to see what might be new or changed in this edition of the Dietary Guidelines. There’s nothing too revolutionary, but here’s what they say, in part, about fiber: Dietary fiber that occurs naturally in foods may help reduce the risk of cardiovascular disease, obesity, and Type 2 diabetes.
We pretty much already knew that. Here’s what else it said: The AI for fiber is 14 g per 1,000 calories, or 25 g per day for women and 38 g per day for men.
The abbreviation “AI” stands for “Adequate Intake.” So, there isn’t really any big change for how much fiber we all should aim for. Men need more than women, which makes sense. Also, if you need to consume more calories, you need more fiber.
Soluble Fiber: Nature’s Gel
Last week we looked at insoluble fiber, or roughage. This week we’ll look at another type of fiber, called soluble fiber. Neither insoluble nor soluble fiber is digested. Soluble fiber, however, attracts water and forms a gel in the digestive tract. One way to picture this (if you’re curious) is to visualize the fiber supplement Metamucil. If you’ve ever taken or seen this supplement, you probably know that you mix the powder with water. You’re then supposed to drink it right away. If you let Metamucil sit for a bit, it becomes very thick and almost gelatinous. This is because Metamucil contains psyllium, a seed husk that is very high in soluble fiber. So picture this happening in your digestive tract. Anyhow, here are the different types of soluble fiber:
- Pectin is a polysaccharide, which is a type of carbohydrate. Pectin is found in all plant foods, but some plant foods contain more than others. Beans, legumes, citrus fruits, apples, bananas, and carrots are high in pectin. Pectin is extracted from fruit and used for jam-making and for thickening foods for people who have difficulty swallowing. It’s also used in medicines to treat diarrhea, constipation, and heartburn.
- Beta-glucans are another type of soluble fiber that are found in the cell walls of bacteria, fungi, and plants. Oats, barley, mushrooms and baker’s yeast are rich sources of this type of fiber. They are used medicinally to treat skin conditions and boost the immune system and are even given as injections to help treat cancer.
- Guar gum is a type of fiber from the seed of the guar plant, which is grown primarily in Pakistan and India. Guar gum is used quite a bit in the food manufacturing industry as an inexpensive food thickener, particularly in foods such as ice cream and pudding. It’s also used in some lotions and creams. Guar gum had been used in diet aids to create a sense of fullness, but its use was banned by the FDA as an ingredient in non-prescription diet pills in the 1990’s due to the risk of intestinal blockage.
- Psyllium is a seed that comes from the plant plantago ovata, which is grown in Iran and India. The husk of the seed is used in the food industry to thicken foods, and this husk is very rich in soluble fiber. Psyllium can swell up to ten times its original volume. For this reason, psyllium is used to treat both constipation and diarrhea.
What it does. Different types of soluble fiber are used to treat constipation and diarrhea and may be helpful for those with irritable bowel syndrome. Here’s what else it does:
- Lowers cholesterol. Because of its water-binding properties, soluble fiber is used to help lower cholesterol. It does this by forming a gel and binding to food cholesterol and bile, which end up being excreted. The body needs cholesterol and bile, so it uses blood cholesterol, instead, which, in turn, lowers the amount of cholesterol in the blood. Also, the soluble fiber gets fermented by intestinal bacteria, which make a type of fatty acid that can block cholesterol formation in the liver.
- Lowers blood glucose. Soluble fiber may help to slow the absorption of glucose into the bloodstream. So, rather than a heavy glucose load hitting your system after eating a meal, the glucose has more of a “trickling” effect. Glucose levels may not rise as quickly after eating (which is a good thing!).
Food sources. The following foods are high in soluble fiber:
- Psyllium (found in some fiber supplements and some cereals)
- Legumes (beans, peas, lentils)
- Citrus fruits
- Apples and pears
- Sweet potatoes
How much? There isn’t a specific amount of soluble fiber to aim for in the Dietary Guidelines, but some authorities recommend getting between 5 and 10 grams a day (as part of your daily total fiber intake).
More fiber fun next week!
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