When a patient reports constipation, I immediately follow up with questions about their consumption of water and fiber. In my clinical experience, 90 percent of the constipation cases that I’ve encountered were due to nothing more than dehydration and the lack of roughage (fiber).

I will write more about the importance of hydration in a later blog but for the moment I want to focus on the different types of fiber and their various functions in the body. Fiber does a lot more than prevent constipation.

Types of Fiber

Insoluble fiber keeps you regular and strengthens your intestinal muscles. This strong fiber is found in plant cell walls and cannot dissolve in water or be digested, so it passes through the intestinal tract intact while a number of benefits: promoting regularity, reducing cardiovascular and type 2 diabetes risk factors; helping maintain healthy weight; and curbing appetite.

Good sources include wheat bran, brown rice, beets, bananas, apples, figs, pumpkins, all leafy greens, berries, and beans.

Soluble fiber. This viscous fiber glues plant cells together, dissolves in water and swells up, forming a gel that grabs bile (or blocks uptake) and eliminates it , forcing the liver to pull more cholesterol from the bloodstream to make more bile, indirectly helping to reduce “bad” LDL cholesterol. It also helps to regulate blood glucose and lower blood pressure, takes out toxins and is fermentable, meaning it supports good bacteria, keeping your immune system strong. An extra benefit to soluble fiber is that is helps with reduce bloating and unwanted flatulence.

Some of the top sources of soluble fiber are: all beans, oatmeal, brussels sprouts, oranges, flaxseeds, barley, pears, potatoes, psyllium, and prunes.

Resistant fiber. Resistant fiber is a type of dietary fiber naturally found in many carbohydrate-rich foods such as potatoes, grains, and beans, particularly when cooled. It called resistant fiber or resistant starch because it “resists” digestion and passes through the upper GI tract, relatively untouched until it reaches the large intestine where it is fermented. One of the by-products of the fermentation process is butyrate, a fatty acid which can blocks the liver’s ability to burn carbohydrates and as a result the body prioritizes fat as an energy source. When the body uses fat as an energy source, the result is weight loss.

One study found that replacing just 5.4% of total carborhydrate intake with resistant starch created a 20 to 30% increase in fat burning after a meal. In cooked starchy foods, resistant fiber/starch is created as the food cools. Cooking triggers starch to asbsorb water and swell, and as it slowly cools, portions of the starch become crystallized into a “resistant” form. Cooling either at room temperature or in the refrigerator will raise levels of resistant starch/fiber. 

Sources include pastas, under-ripe bananas, potatoes, legumes (richest source), oatmeal, and rice. When you heat these foods up, the resistant starch is gone. So let that hot potato cool and fried rice stir fry cool in the refrigerator. 

Many patients ask for a quick fix and ask about fiber supplements. There are definitely instances where I would recommend certain products, but they cannot replace the abundant benefits received by consuming the fiber contained in a variety of fruits, vegetables, seeds, nuts, mushrooms, and whole grains.