Difference Between Soluble and Insoluble Fiber

Main Difference –  Soluble vs  Insoluble Fiber

Dietary fibers are constituents that are resistant to digestion but they are enormously helpful constituents of our diets. Thus, it is an essential nutrient in your daily diet because it helps to remove waste and toxic compounds from the foods you eat. In addition, it helps to prevent many diseases, such as constipation, hernia, diverticulosis, intestinal cancers, metabolic syndrome and type II diabetes. In addition, fiber-rich foods take a longer time to digest and thereby contribute to the feeling of fullness and satiety for a longer period of time. Slow absorption also slows down the entrance of glucose into the blood and thereby prevents huge blood glucose and insulin spikes. Furthermore, diets high in fiber also decrease the risk of cardiovascular diseases since fiber helps the human body to excrete the excess cholesterol in your blood. There are two forms of dietary fiber known as soluble and insoluble fiber. Soluble fiber is soluble in water and turns into a gel during digestion whereas insoluble fiber is not soluble in water. This is the main difference between soluble and insoluble fiber. Soluble fiber shares many similarities with insoluble fiber, but they do have some differences. The purpose of this article is to highlight the distinguish characteristics between soluble and insoluble fiber.

What is Soluble Fiber

Soluble fibers can dissolve in water and turn into a gel during gastrointestinal digestion. This process results in a slow digestion. Slow digestion, directly contributes to absorbing more vitamins and minerals, as well as other nutrients. This type of fiber is mainly found in oat bran, barley, nuts, seeds, beans, peas, lentils, and some fruits and vegetables. Psyllium, a common fiber supplement is a rich source of soluble fiber. Some types of soluble fiber may help lower risk of heart disease and type II diabetes. It also contributes to weight control in the human body.

Flax seeds are a source of soluble dietary fibers.

What is Insoluble Fiber

Insoluble fiber cannot dissolve in water, and it is mainly originated in foods such as wheat bran, vegetables, and whole grains. These types of fiber can add bulk to the fecal matter and appears to help digested food pass more rapidly through the intestinal tract. Insoluble fiber remains relatively stable or non-reactive and removes waste throughout your digestive tract. As a result, insoluble fibers directly contribute to easy bowel movements, easy defecation, and prevent colon cancer development. If food is rich in insoluble fiber, it is resistant to digestion, and can be found in your fecal matter.

Wheat brain is rich in insoluble fibers.

Difference Between Soluble and Insoluble Fiber

The difference between soluble and insoluble fiber can be divided into following categories. They are; 

Solubility in Water

Soluble fiber is soluble in water.

Insoluble fiber is not soluble in water.

Examples

Soluble fiber:

• Fructans
• Inulin – in chicory and asparagus
• Pectin –in the fruit skin (mainly apples), vegetables
• Carrageen – in red algae
• Raffinose – in legumes
• Xylose
• Gums
• Mucilages
• Some hemicelluloses

Insoluble fiber:

• Cellulose – in cereals, fruit, vegetables
• Hemicellulose – in cereals, bran, timber, legume
• Chitin – in fungi, exoskeleton of insects and crustaceans
• Lignin – in stones of fruits, vegetables, and cereals
• Xanthan – produced by Xanthomonas-bacteria
• Some hemicelluloses

Recommended Intake

It is recommended that an adult should take in 20 – 35g of fiber each day and this amount should consist of both soluble and insoluble fiber since each type provides different health benefits. Your diet should have 3:1 ratio of insoluble to soluble fiber.

The daily diet should comprise less soluble fiber compared to insoluble fiber.

The daily diet should comprise more insoluble fiber compared to soluble fiber.

Common Plant Sources

Soluble fiber can be found in  oats and oatmeal, rye, chia, barley, legumes (peas, beans, lentils), fruits (figs, avocados, berries prunes, ripe bananas, and the skin of apples, quinces and pears) vegetables (broccoli and carrots,) root tubers, flax seeds and nuts.

Insoluble fiber can be found in bran layers of cereal grains, whole grain foods, legumes (beans and peas), nuts and seeds, potato skins, vegetables (green beans, cauliflower, zucchini, celery etc.) some fruits such as avocado, unripe bananas, the skins of some fruits such as kiwifruit, grapes and tomatoes.

Chewing Properties

Soluble fiber is soft and easy-to-chew.

Insoluble fiber is very tough and hard-to-chew.

Health Benefits

Soluble fiber contributes to lowering cholesterol levels, reducing the risk of colon cancer, losing weight, prevent irritable bowel syndromes such as diarrhea or constipation and abdominal discomfort and lowering blood glucose levels. Also, during fermentation of soluble fiber short-chain fatty acids are produced which contribute to different health benefits such as stimulate the production of T helper cells and antibodies having vital roles in immune protection.

Insoluble fibers absorb water as they move through the gastrointestinal tract, thereby softening stool, and reducing the transfer time through the intestinal tract, facilitating easy defecation, and reduction in the risk and occurrence of hemorrhoids and constipation.

In conclusion, both soluble and insoluble fibers are vital in your daily diet, and you need to incorporate approximately equal amounts of both. Both insoluble and soluble sources are found in similar plants, and they are resistant to digestion by human digestive enzymes.

References

Anderson JW, Baird P, Davis RH, et al. (2009). Health benefits of dietary fiber. Nutr Rev 67(4): 188–205.

Brown L, Rosner B, Willett WW and Sacks FM (1999). Cholesterol-lowering effects of dietary fiber: a meta-analysis. Amer J Clin Nutr 69(1): 30–42.

Eastwood M and Kritchevsky D (2005). Dietary fiber: how did we get where we are? Annu Rev Nutr 25, 1–8.

Image Courtesy:

“WheatBran” by Alistair1978 assumed (based on copyright claims). –  Own work assumed (based on copyright claims). (CC BY-SA 2.5) via Commons 

“Brown Flax Seeds” by Sanjay Acharya – Own work. (CC BY-SA 3.0) via Commons 

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