Dietary fiber – what’s in it?

Article by  Karolina Jakiel

Dietary fiber consists of substances of vegetable origin belonging to carbohydrate food group. Dietary fiber is not digested and absorbed in the small intestine, but undergoes partial or complete fermentation in the large intestine. Fiber induces local reactions associated with the presence in the digestive system, and systemic reactions affecting metabolism.

The fiber consists of the following substances that are soluble in water: cellulose, hemicellulose, lignin. There are also pectins, gums and mucilage that do not dissolve under the influence of water.

Health-promoting effect of fiber:

– products containing dietary fiber have a protective effect if there is a risk of cancer of the large intestine, pancreas and colon.

There are several processes to protect against cancer, including shortening the time of intestinal transit, increasing the stool volume, binding bile acids and carcinogenic compounds, increasing the pH of the intestinal content, stimulating the development of beneficial microflora and stimulating fermentation in the large intestine.

-the presence of fiber results in a faster feeling of satiety, which lasts longer. A high fiber diet is a good solution for people on a weight loss diet and for people who have a snacking problem.

-cellulose and lignin, or insoluble parts of fiber, do not decompose through the intestinal flora, which has a beneficial effect on the acceleration of intestinal peristalsis, as well as limiting the energy value of food

-foods with a lot of fiber reduce the postprandial response of insulin and glucose. In this way, they improve the lipid profile and have a beneficial effect on the treatment of diabetes.

-cellulose, hemicellulose and lignin, i.e. the soluble fiber parts, absorb bile salts in the intestine. As a consequence, this leads to a reduction in total cholesterol, triglycerides and LDL.

– fiber plays a key role in the treatment of constipation. The water soluble fractions become a gel, which limits the intestinal transit and the absorption of other substances. Fatty acids and bile acids are transformed into substances of a laxative character. During the fermentation an increased amount of carbon dioxide and methane are formed. These substances increase the mass of stool and soften it.

-short-chain fatty acids lower the pH, increase the amount of intestinal flora bacteria, which in turn causes a reduction in the amount of pathogenic bacteria and the increase of the gastrointestinal epithelium.

Basic functions of water-soluble fiber

→ regulation of intestinal peristalsis, increase of fecal mass volume, reduction of intestinal transit time

→  postprandial glycemic control

→ lowering of total cholesterol, LDL cholesterol, triglycerides

→ regulation of bile acid metabolism, prevention of gallstones

→ increasing the feeling of fullness

→ prebiotic operation

→ lowering of blood pressure

→ removing toxins from the body

Basic functions of water-insoluble fiber

→ beneficial action in constipation

→ stabilization of sugar level

→ regulation of lipid metabolism

→ prevention of cholelithiasis

→ reduction of body weight

→ prevention of colon cancer

→ lowering of blood pressure

→ removing toxins from the body

How much fiber should you provide?

Terapeutic Life Changes recommends eating 20-30 g fiber daily for the prevention of cardiovascular diseases. In diabetes, this amount increases to 50g.

Current WHO recommendations say about 25-40 g per day. The upper limit of intake is recommended in the case of intestinal problems or when using a high-protein diet.

It is also worth paying attention to the amount of water drunk. A minimum of 2 liters of water should be drunk daily. If you drink too little, you may get constipation. 

It was found that an excessive intake of fiber will disturb the absorption of fats and thus fat-soluble vitamins (A, D, E, K).

Phytic acid associated with fiber limits the absorption of calcium, zinc and iron.

Too much fiber can cause diarrhea.

There are diseases in which fiber intake is limited or even forbidden. These include: inflammation of the stomach, pancreas, bile ducts, intestines and anemia.

Where to find fiber?

Soluble fiber occurs in

– fruits (plums, bananas, pulp of apples and pears, apricots, peaches)

– vegetables (broccoli, carrots, Brussels sprouts, artichokes, kohlrabi, potatoes, onions),

– cereal products (oatmeal, rice, groats, bran)

– legumes (soybeans, beans)

– psyllias plantain seed husks

Insoluble fiber is found in:

– wholegrain food

– wheat bran, barley bran, corn

– nuts

– pumpkin, sesame and sunflower seeds

– vegetables (cauliflower, Chinese cabbage, tomatoes, spinach)

– fruit (raspberries, avocados, bananas, kiwi)

Karolina Jakiel – master of dietetics specialist in psychodietetics.
She obtained her master’s degree at the University of Rzeszow in Poland, completed post-graduate studies in psychodietetics at the University of Social Sciences and Humanities (SWPS University) in Katowice in Poland.
During her studies, she participated in numerous courses and trainings, among others: diagnostics in the office of a dietician, insulin resistance, psychodietetics, sports dietetics, oncological dietetics, and diet for the elderly.
During her studies she took an active part in the activities of the Scientific Circle of Dieticians at the University of Rzeszow.
She is interested in healthy eating and shares her ideas through her profile in social media.

About Dr Antonella Grima

Dr. Antonella Grima M.D. M.Sc. Pg.Dip. is the founder of the Health and Nutrition Centre in Luqa, Malta. She is a Medical Doctor specialised in Public Health as well as a Registered Nutritionist. Read More >

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