Adequate dietary fiber intake is essential for overall health and disease prevention. Let’s figure out what dietary fiber is, why and how much we need it and where to get it from.
What is fiber?
Most readers probably know that dietary fiber is found in vegetables, fruits, berries, legumes, whole grains, nuts and seeds, in short, in all plant foods. What else do all these foods have in common besides the fact that they are all plants? These foods are mostly composed of carbohydrates. Dietary fiber is, technically speaking, indigestible polysaccharides, or complex carbohydrates (poly = a lot; saccharide = sugar). These polysaccharides are responsible for the structure of plants, it is thanks to them that vegetables and fruits have their appearance. Take a celery stalk, for example. Do you see long, longitudinal “threads” on it? That is dietary fiber. Celery is a radical example. Fibers are not always visible to the naked eye.
Types of dietary fiber
We can categorize fiber into two main categories: soluble and insoluble. Soluble fiber is viscous, water soluble and fermentable. Soluble fibers are also known as prebiotics. They feed beneficial bacteria (probiotics) in our intestines. Soluble fiber lowers blood cholesterol and glucose levels. It also holds moisture in the stool, softening it. Insoluble fibers leave our body in the same form in which they enter it. This is to say our body does not break them. They increase stool volume and improve bowel motility. Insoluble fiber provides a feeling of fullness/satiety. Both types of fiber should be present in our diet every day.
Soluble and insoluble fiber are further divided into sub-categories. I will briefly tell you about the most famous ones. The soluble group includes beta-glucans, pectin, inulin, gums. Among Insoluble fibers are cellulose, lignins and resistant starch. A well-known psyllium fiber, often prescribed against constipation, possesses qualities of both soluble and insoluble fibers.
Soluble beta-glucans (β-glucans) are found in the cell walls of the grain endosperm. Beta-glucans are very important for health. It is scientifically proven that beta-glucans help sustain healthy cholesterol levels. The best sources of β-glucans are barley and oatmeal.
We find pectin in apples, apricots, quince and citrus fruits. Citrus peels contain a lot of pectin, about 30% by weight. Pectin contributes to maintaining normal cholesterol level and helps improve postprandial (=after meal) rise of blood glucose. Pectin in its pure form is used as a thickener in food, such as jams and preserves.
Inulin has a pronounced prebiotic activity. It feeds the good bacteria in our intestines, thus improving the intestinal flora. Inulin is often used to fight diarrhoea and irritable bowel syndrome. We find inulin in chicory, bananas, asparagus, garlic and wheat.
Insoluble fiber lignin makes vegetables hard and crunchy. Food sources of lignin are root vegetables, wheat and seeds. Lignin has not been studied as intensively as other types of fiber. It is believed to have strong anti-oxidant properties.
Insoluble fiber resistant starch is not digested and passes through the digestive system unchanged. Resistant starch is known for significantly reducing appetite. Good sources of resistant starch are green (unripe) bananas, legumes, cooked and chilled potatoes, and chilled white rice.
Additional health benefits of dietary fiber
In addition to regulating cholesterol in the blood, fiber slows down the flow of glucose into the blood. Adequate fiber intake reduces the risk of cardiovascular disease, type 2 diabetes and some types of cancer. It is believed that regular, adequate intake of dietary fiber can reduce the risk of intestinal cancer by as much as 40%. Dietary fiber dilutes, binds and quickly removes potential carcinogens from the intestines. They also create a feeling of fullness and thus control weight.
How much fiber do we need and where do we get it? Nutritional advice for every day
The recommended daily allowance (RDA) for men is 40 grams and 30 grams for women.
Some practical tips for every day for those who want to make sure they are eating enough fiber:
- Read labels. The amount of dietary fiber is always indicated on labels.
- Eat raw vegetables and fruits every day. Eating a whole orange (or two) is better than drinking a glass of orange juice. Remember, the World Health Organization (WHO) recommends a daily intake of at least 400 g of vegetables and fruit per day (we are talking about the total intake of fruit and vegetables).
- Eat vegetables and fruits along with their skin as much as possible.
- When possible, go for wholegrain foods: wholegrain pasta, wholegrain bread, unbleached grains. If you are into baking, use whole grain flour instead of regular white flour.
- Add lentils and beans to salads and soups.
- Eat a handful of nuts every day.
- Sprinkle seeds (sunflower, pumpkin, hemp, chia, etc,) on yoghurt, cereals, salads and soups.
Can you eat too much fiber?
Can you eat too much fiber? Certainly. Is it dangerous? Sometimes. Despite fibers’ health benefits, too much fiber in the diet on a regular basis can be harmful. Especially for persons with low weight, too much fiber can have negative consequences for their health. Fiber provides a feeling of fullness. So potentially a person whose diet contains lots of fiber can eat less (meaning less calories and less nutrients than necessary) than they need.
Small children who eat an exclusive vegan diet can get too much fiber which prevents them from eating enough and thus results in growth retardation.
Switching from a low-fiber to high-fiber diet can cause abdominal pain, bloating and excessive flatulence. To prevent these undesirable side effects, it is recommended to increase fiber intake gradually over the course of several weeks. Drinking enough water helps to soften the fibers as they move through the gastro-intestinal (GI) tract.