Why fiber matters

Types of soluble fiber serve as prebiotics to enhance gut health and so much more.

Dietary fiber is more than just roughage to keep you regular. Soluble fiber—the kind that dissolves in water and turns into a gel—also has a prebiotic function and benefits health in a number of vital ways.

Digestive health

Soluble fiber can improve irritable bowel syndrome and leaky gut. A high fiber diet is also associated with a reduced risk of colon cancer. There are two main ways soluble fiber helps keep the digestive tract healthy.

First, soluble fiber that’s fermented in the colon serves as a prebiotic. A prebiotic is broken down by the good bacteria in the colon to create beneficial metabolites. The most important of these metabolites are short-chain fatty acids, which can nourish the cells lining the colon and reduce inflammation.

Second, unfermented or non-fermentable soluble fiber can soak up and hold water in the gut. This has a regulating effect on bowel movement, helping to avoid both hard and loose stools as in constipation and diarrhea.

Top gut-friendly soluble fibers from food include inulin (e.g., onions and chicory root), fructooligosaccharides (e.g., bananas and asparagus), resistant starch (e.g., grains and legumes) and pectin (e.g., apples and grapefruit).

Weight management

Higher fiber intakes have generally been linked to lower rates of overweight and obesity. One particular soluble fiber, glucomannan, has demonstrated effectiveness as a weight loss aid in some studies.

Extracted from the root of the konjac plant, glucomannan is among the most viscous of soluble fibers known, absorbing up to 50 times its weight in water. This property makes glucomannan especially filling and digestion slowing, allowing one to eat less and stay satisfied longer. Glucomannan also influences the levels of hunger-regulating hormones to help curb appetite.

Since glucomannan is fermentable, it may additionally enhance weight control through the action of short-chain fatty acids. These metabolites have been found to increase fat burning and decrease fat storage.

Blood sugar control

Soluble fiber slows the digestion and absorption of carbohydrates. That’s why carbohydrate foods containing soluble fiber have lower glycemic indexes and are less likely to spike blood sugar levels. The prebiotic action of soluble fiber also contributes to healthier blood sugar metabolism.

A diet high in soluble fiber can lower the risk of developing type 2 diabetes. For people with diabetes, consuming more soluble fiber helps improve blood sugar control and insulin sensitivity. Natural sources of soluble fiber include beans and lentils, broccoli, carrots, apples, citrus fruits, oats, flaxseeds and psyllium husks.

Cardiovascular health

Fiber-rich foods such as whole grains, vegetables and fruits appear to protect against cardiovascular disease, including stroke and heart disease. Soluble fiber has been shown to decrease two key risk factors for cardiovascular disease: high blood cholesterol and inflammation.

For cholesterol, soluble fibers interfere with the absorption of fat and cholesterol from food and promote their elimination. This leads to lowered levels of blood lipids, especially the “bad” LDL cholesterol. For this purpose, psyllium husk fiber has been found effective.

For inflammation, fermentable soluble fibers such as that from oats are best, as they stimulate the production of short-chain fatty acids, which help reduce inflammation throughout the body.


Amazingly, soluble fiber is also an immune booster. The immune system is closely linked with the gut. Metabolites produced by good gut bacteria can increase the activity and function of immune cells. As a result, the body can gain a better ability to fight off infection-causing microbes such as the cold virus, as well as to eliminate abnormal cells in defense against cancer.

A particular type of soluble fiber, beta-glucan, has well-studied immunity-enhancing properties, and is even being used as an experimental cancer therapy. For everyday health maintenance, beta-glucans can be obtained from food sources such as oats, barley, shiitake mushrooms, seaweed and yeast.

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Interested in getting more prebiotic fiber? Observe some precautions first. To avoid bloating and other digestive symptoms, it’s best to increase fiber intake gradually. Also, individuals sensitive to FODMAPs should be extra careful with the types and amounts of fiber foods or supplements. Soluble fibers in the FODMAP group of short-chain fermentable carbohydrates include galactooligosaccharides (e.g., beans) and fructans or fructooligosaccharides (e.g., wheat, onions and chicory root). With some experimenting, you may find a happy balance that helps you live a healthier life.

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