Q: I eat a lot of fiber, but now I hear that I need two kinds – soluble and insoluble. What the hell does that mean? Where can I get these types of fiber?
A: It’s good to hear that you’re eating lots of fiber. Traditionally, fiber has been separated into the two categories: soluble and insoluble fiber.
Soluble fiber is the one that aids in decreasing serum cholesterol levels (I’m sure everyone’s familiar with this due to all the Quaker Oats commercials). Soluble fiber is commonly found in oats, legumes, barley, apples, strawberries, and citrus.
Insoluble fiber is pitted as the one with no effects on cholesterol levels but effective at increasing stool size. Insoluble fibers can be found in spinach, broccoli, carrots, other vegetables, and whole grains.
Most recently the Food and Nutrition Board (FNB) proposed new definitions for fiber saying the soluble/insoluble characterization was no longer accurate or relevant because research has shown that not all soluble fibers lower cholesterol; both soluble and insoluble fibers can increase stool size; and certain insoluble fibers having no efficacy in relieving constipation.
The two new categories of fiber are dietary and functional. They are defined as the following:
“Dietary Fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. Functional Fiber consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humans. Total Fiber is the sum of Dietary Fiber and Functional Fiber.” (Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005)”.
Basically, the new definitions for fiber can be simply stated: “If the fiber is found in its natural setting and has not been chemically modified (i.e. pectin in an apple or beta-glucan in oatmeal), then it is considered dietary fiber.”
Their claim is that these new definitions for fiber will allow greater flexibility in classification as the food science of fiber progresses. Personally, I don’t find these new definitions to be relevant for the average consumer and they can be rather confusing.
For example beta-glucan, which is commonly found in oatmeal, can be considered both a dietary and functional fiber depending on whether it’s been extracted from the oats or not. Plus there is no real benefit for someone to eat functional vs. dietary fiber. At least with the old definitions there were different general health benefits from eating one vs. the other.
In the end, the FNB only gives a recommended intake level for total fiber (38 g/d Males ages 19-50y; 25/gd Females ages 19-50y) and not dietary fiber and/or functional fiber.
As a health and performance conscience person, getting enough fiber should be your main focus. If the average T-Nation reader is “eating like he should” with fruits or vegetables at every meal and whole grains in the morning or after exercise (depending if you are a Temporal Nutrition or Massive Eating person), then he’ll be getting adequate levels of all the necessary types of fiber.
This article was originally published as part of the Man Fuel Column on T-Nation.
