Why Do We Need Fiber and Where Do We Get It?

Dietary fiber is the set of components found in foods of plant origin, whose main characteristic is that they cannot be digested by our body. Although they do not provide us with nutritional substances, it is essential for our body to be able to function correctly. Our intake is important not only for its benefits at the intestinal transit level but also for those related to other metabolic processes. They are structural polysaccharides of plants, including cellulose, hemicellulose, beta-glucans, pectins, mucilage, and gums. Lignin, also from plants, is an insoluble fiber with no polysaccharide structure because it is a polymer of phenylpropane. The structural differences of each of them determine different physical-chemical properties and, as a consequence, diverse physiological behaviors.

Most plant-based foods contain fiber of 2 types: soluble and insoluble, in different amounts:

• Soluble Fiber: Soluble fiber is one that absorbs a large amount of liquid during its passage through the digestive tract, forming viscous gels after hydration. It includes, among other components, resistant starch, pectins, gums, mucilage, some hemicelluloses, and non-starch polysaccharides.
• Insoluble Fiber: Insoluble fiber does not retain fluids when in contact with it, and, unlike soluble fiber, it is hardly fermented by bacteria in our intestines. It includes cellulose, some hemicelluloses, and lignins, as well as other polyphenols. This type of fiber helps accelerate the passage through the intestine by increasing the stool volume and accelerating the transit through the stomach, therefore being of great help to resolve constipation.

1. Bowel function: Dietary fiber, especially insoluble type, helps prevent constipation by increasing stool weight and reducing the duration of intestinal transit. This effect is even more significant if consumption is accompanied by an increase in water intake. Short-chain fatty acids, produced when fiber ferments due to the action of intestinal bacteria, are an essential source of energy for colon cells and can inhibit the growth and proliferation of cancer cells in the intestine. By improving intestinal function, dietary fiber can reduce the risk of diseases and disorders, such as diverticular disease (bags or sacs that form in the lining of the colon) or hemorrhoids.
2. Control of obesity: It has a satiating effect due to its slow digestion and its ability to retain water; this is why it helps to control the intake of other foods. It has a low caloric intake compared to other nutrients, which is why it helps control weight.
3. Cholesterol control: Soluble fiber forms a kind of gel when it absorbs water; this gel binds in the digestive tract with bile acids, necessary for the absorption of cholesterol and other lipid compounds. This causes them to be eliminated through the stool and thus reducing cholesterol absorption. Also, the fermentation of the fiber favors the formation of short-chain fatty acids, which help to inhibit the synthesis of hepatic cholesterol. Research has shown that those people who increase their soluble fiber intake by 5-10 g per day have a 5% decrease in their LDL cholesterol.
4. Glycemic control: The soluble kind works at three levels-

• In the stomach, it produces a sensation of fullness, reducing the intake.
• In the small intestine, it forms a gel-like solution, which absorbs part of the ingested carbohydrates, decreasing the absorption of glucose.
• In the large intestine, short-chain fatty acids (obtained from their fermentation) can improve insulin resistance in diabetes, favoring glycemic control.

In order to benefit from the full effects, it is important to vary the sources we obtain it from in our diet. Diets with fruits, vegetables, lentils, beans or chickpeas, whole grains, bread, and nuts provide not only dietary fiber but also provide other nutrients and dietary components essential for optimal health.

An excessive and careless intake of this plant component can cause severe damage to the body. One of the dangers of  too high an intake is that by not allowing glucose to pass directly into the bloodstream, it can decrease the absorption of essential minerals for the body such as calcium, iron, zinc, and copper. In addition, too much intake can cause lower digestibility because although it can contribute to weight loss and slow gastric emptying, it can, in turn, lead to greater bloating, gas, and flatulence. For this reason, fiber consumption is discouraged in individuals with gastritis or who need to take special care of their stomachs.

Over consumption has also been shown to reduce and inhibit the activity of pancreatic enzymes that can disrupt the normal digestion of proteins, fats, and carbohydrates, which can lead to digestive problems.

Vegetables are the largest and most natural source of fiber. The richest in this component are lettuce, chard, raw carrots, spinach, cooked tender vegetables, broccoli, artichokes, pumpkins, potatoes, green beans, and vegetable juices. There is also a high amount of this plant based nutrient in legumes and nuts such as sunflower seeds, almonds, pistachios, and walnuts.

The fruits that contain the most fiber are apples, bananas, peaches, pears, tangerines, plums, figs, and other dehydrated fruits. Another of the most important primary sources of fiber are cereals: wheat and its derivatives, whole wheat bread, brown rice, high-fiber cereals, whole-wheat pasta, and so on.