Dietary fiber makes up 99% of the structure of plants and is found in fruits, vegetables and grains. It is not digested by enzymes in the digestive tract and has many effects on the body’s systems, including reduction of blood cholesterol levels, blood glucose levels, risk for heart disease and obesity while preventing cancer. It also improves the function of the large intestines, etc. We can divide dietary fiber into 2 types, namely, soluble fiber and insoluble fiber.
- Soluble fiber is dietary fiber that is can be dissolved in water and absorb dissolved substances in water such as pectin, gums, mucilage, which are indigestible soluble substances found in plant cells and contribute to slower passage of food in the digestive tract. It also helps reduce absorption of cholesterol and is abundantly found in legumes, oats and fruits and vegetables.
- Insoluble fiber is dietary fiber that cannot be dissolved in fiber but will expand in water like a sponge, thereby increasing its volume in the stomach and making you feel full. It also increases the volume of your fecal output and facilitates faster passage of food in the digestive tract. The greater fecal mass that results also shortens the time that food residues remain in the body (faster bowel movements), thus making the body feel like having bowel movements and reducing constipation. This type of fiber includes cellulose, hemicellulose and lignin and is often found on the cell walls of plants. This type of dietary fiber is abundant in rice bran and fruits and vegetables.
Main Effects of Dietary Fiber on the Body
- It lowers cholesterol levels and blood lipid levels and prevents heart disease. Soluble dietary fiber can lower blood and liver cholesterol levels, with effective dietary fiber including pectin and psyllium of different types such as guar gum and bean gum. The sources for these types of soluble dietary fiber include oat bran, barley and legumes. Because they can lower overall cholesterol levels, they can also indirectly reduce overall risk of heart disease, especially coronary artery disease. Consuming dietary fiber from oat and beta-glucan by 3-15 grams per day can lower cholesterol levels by 5-15% (with visible results in people with high cholesterol levels). Meanwhile, insoluble dietary fiber such as cellulose and wheat bran does not affect blood cholesterol levels.
- It improves the function of the large intestine. Insoluble dietary fiber reduces food transit time in the large intestine, increases the weight and frequency of feces in addition to diluting toxins in the large intestine, which normalizes the preparation of nutrients to be digested by bacteria in the large intestine. Sources of insoluble dietary fiber include wheat bran, which significantly increases fecal output and benefits patients with constipation and hemorrhoids, followed by fruits and vegetables. Meanwhile, gums and mucilage moderately increase fecal output while legumes and pectin are least effective in increasing fecal output.
- It prevents colorectal cancer and bowel obstruction. Heavy consumption of dietary fiber reduces the incidence of colorectal cancer and bowel obstruction, while low consumption of dietary fiber causes changes to the gut flora and reduces the accumulation of bile acid while increasing the time for food to remain in the large intestine, decreasing fecal weight and volume and frequency of bowel movements.
- It reduces utilization of nutrients in the small intestines. Food components are digested and nutrients are absorbed through the mucosal cells, and different types of dietary fiber can suppress the function of pancreatic enzymes used to digest carbohydrates, fats and proteins. Dietary fiber may reduce the function of enzymes for breaking down triglycerides, starches and proteins in the gut. Natural dietary fiber such as grains and fruits in general reduce absorption of minerals such as calcium, iron, zinc and copper. However, the reduction in absorption of minerals are partly caused by phytic acid present in food sources.
Recommendations for Daily Consumption of Dietary Fiber
- You should eat rice as a staple, especially brown rice or coarse rice or products from unpolished rice such as wholewheat bread.
- Eat a lot of fruits and vegetables and a wide variety of legumes.
- Eat whole fruits with their peel such as apples, grapes and guava.
- Eat fresh fruits instead of drinking squeezed fruit juices. (1 fresh orange contains 6 times more dietary fiber than squeezed orange juice.)
- Try to eat more whole vegetables, including the leaves and stems, for example, kale, morning glory and bok choy.
- Add various legumes into your food, such as salads, clear soups and curries.
- Drink plenty of water, since dietary fiber works better with the help of water.
- For people who are unfamiliar with consuming large quantities of fresh fruits and vegetables, they should gradually increase the amount of dietary fiber that they consume in order to prevent a disruption in their digestive system.
