Welcome to our guide to dietary fiber, an essential part of a healthy diet that is often overlooked. In this article, we explain fiber, its types and sources, and why it’s so important for our wellbeing.
What is dietary fiber?
While dietary fiber is made up of sugar molecules and is therefore chemically carbohydrates, they are linked together by a special type of chemical bond that cannot be broken down by human digestive enzymes. This means that, unlike other carbohydrates (such as starch and sugar), dietary fiber is not digested and absorbed in the small intestine.
Types of dietary fiber
Traditionally, dietary fibers are divided into soluble and insoluble.
The name says it all. Soluble fiber dissolves in water, whereas this is not the case with insoluble fiber. Let’s stick with these terms for the sake of simplicity.
Soluble fiber resists digestion in the mouth, stomach and small intestine and ends up in the large intestine. Soluble fibres are often metabolized by bacteria in the intestinal microbiome. This produces substances that are useful for the human organism, such as short-chain fatty acids, including acetate, butyrate and propionate, from which energy can be obtained.
Soluble fiber includes various types of plant polysaccharides that can dissolve in water and form a gel-like substance. Here are some important examples:
Pectin: Occurs in large quantities in fruits such as apples, citrus fruits and berries. Pectin is often used in the food industry as a gelling agent.
Beta-glucans: These are found in oats, barley and some mushrooms. Beta-glucans are known to lower cholesterol levels and strengthen the immune system.
Inulin and oligofructose: These fructans are found in plants such as chicory, onions, garlic, leeks and artichokes. Inulin is often used as a prebiotic as it promotes the growth of beneficial gut bacteria.
Guar gum: This is obtained from the seeds of the guar plant and is used as a thickening and stabilizing agent in food.
Psyllium (psyllium husks): Psyllium is a particularly rich source of soluble fiber and is often used to treat constipation and lower cholesterol.
We can quickly see that soluble fiber has numerous functions and health benefits. These have been proven by various scientific studies. Here are some important functions and corresponding studies:
- regulation of blood sugar levels
Function: Soluble fiber slows down the digestion and absorption of carbohydrates, which leads to a smoother rise in blood sugar levels.
Study: A meta-analysis of 35 studies has shown that soluble fiber can improve glycemic control and lower HbA1c levels in people with type 2 diabetes.
Meta-Analysis of Fiber in Glycemic Control: PubMed
- lowering cholesterol levels
Function: Soluble fiber can bind bile acids and promote their excretion, which can lower blood cholesterol levels.
Study: A review of studies showed that the consumption of beta-glucan from oats can significantly lower total and LDL cholesterol levels.
Effect of Beta-Glucan on Cholesterol Levels: Journal of Nutrition
- promotion of intestinal health
Function: Soluble fiber serves as a prebiotic that promotes the growth of beneficial gut bacteria, which can lead to improved gut health and immune function.
Study: A study has shown that inulin promotes the growth of bifidobacteria in the gut and can thus improve gut health.
Inulin and Gut Health: American Journal of Clinical Nutrition
- weight management
Function: By delaying gastric emptying, soluble fiber contributes to a longer feeling of satiety, which may help reduce calorie intake.
Study: A systematic review found that increased fiber intake is associated with reduced energy intake and lower body weight.
Fiber Intake and Weight Management: The Journal of Nutrition
- reduction in the risk of cardiovascular disease
Function: Through their positive effects on blood sugar and cholesterol levels, soluble fiber can reduce the risk of cardiovascular disease.
Study: A comprehensive meta-analysis of cohort studies showed that a high fiber intake is associated with a lower risk of coronary heart disease and stroke.
Fiber and Cardiovascular Disease Risk: BMJ
Insoluble dietary fiber
Insoluble fibers resist digestion and pass through the digestive system intact. Their main role is to aid the transportation of other foods and liquids. They help to increase stool bulk and speed up intestinal transit, which has various health benefits. In contrast to soluble fiber, which forms a gel-like substance in water, insoluble fiber remains intact, binds liquid in the intestine and promotes digestion through mechanical stimuli.
Examples of insoluble fibers
Cellulose: Found in vegetables, whole grains, nuts and seeds.
Hemicellulose: Found in whole grains and cereal bran.
Lignin: Found in root vegetables, fruit peel and seeds.
Insoluble fibers also have a variety of positive effects and functions in the human body, which can be proven by scientific studies:
- promotion of intestinal health
Function: Increasing the volume of stool and speeding up the passage of food through the intestines, which promotes regularity and prevents constipation.
Study: One study found that insoluble fiber such as wheat bran can shorten intestinal transit time and increase stool frequency.
Dietary fiber and body weight Slavin JL.
- prevention of diverticulosis
Function: Formation of softer and bulkier stools, reducing the risk of developing diverticula in the colon.
Study: A prospective study showed that a diet rich in fiber, especially insoluble fiber, can reduce the risk of diverticular disease.
A prospective study of dietary fiber types and symptomatic diverticular disease in men. Aldoori WH, et al.
- reduction of the risk of colorectal cancer
Function: By promoting rapid passage of food through the digestive tract, insoluble fiber reduces the exposure time of the intestinal mucosa to potentially carcinogenic substances.
Study: A meta-analysis of cohort studies suggests that a high intake of insoluble fiber is associated with a lower risk of colorectal cancer.
Dietary fiber intake and risk of colorectal cancer: a pooled analysis of prospective cohort studies. Park Y, et al.
- weight management
Function: Insoluble fiber contributes to satiety through its bulking effect, which may help reduce calorie intake and control body weight.
Study: One study showed that an increased intake of insoluble fiber is associated with less weight gain over several years.
Dietary fiber and weight gain: a study of 6 years Tucker LA, et al.
Summary of sources of dietary fiber
To achieve a balanced fiber intake, a variety of fiber-rich foods should be consumed, as different types of fiber are present in different proportions.
Soluble fiber
-Oats (e.g. oat flakes, oat bran)
-Pulses (e.g. lentils, beans, peas)
-Fruits (e.g. apples, oranges, grapefruits, berries)
-Vegetables (e.g. carrots, sweet potatoes, broccoli)
-Barley (e.g. barley porridge, barley soup)
-Chicory and Jerusalem artichokes (e.g. as salads, cooked side dishes)
Insoluble fiber
-Wholemeal products (e.g. wholemeal bread, wholemeal rice, oat flakes)
-Bran (e.g. wheat bran, oat bran)
-Vegetables (e.g. cauliflower, green beans, potatoes with skin)
-Nuts and seeds (e.g. almonds, walnuts, linseed)
-Fruit with skin (e.g. apples, pears, grapes)
-Root vegetables (e.g. carrots, turnips, parsnips)
Daily intake of dietary fiber
Although it is important to ensure a sufficient intake of dietary fiber, a reasonable upper limit should be set at the same time. The following also applies to dietary fiber: a healthy amount is crucial. Excessive consumption of fiber can lead to the following problems: Gas formation, bloating, digestive problems (flatulence, cramps, constipation or diarrhea), nutrient deficiencies (mineral deficiencies such as iron, calcium, magnesium, zinc), impaired drug effects (reduced drug absorption), changes in bowel habits (irregular bowel movements). Therefore, the USDA dietary guidelines recommend 14 grams of fiber per 1,000 calories consumed. This amount should be sufficient for most people to ensure normal digestion and nutrient absorption and to take full advantage of the benefits of fiber
Conclusion
Fiber is an essential part of a healthy diet and offers numerous health benefits. While it is important to meet the recommended daily intake, focusing on whole, unprocessed foods rich in fiber can naturally meet your needs. Including fruits, vegetables and legumes in your diet will ensure that plenty of fiber is consumed.
Understanding fiber allows you to make better choices for your health. Fiber should be part of your daily routine so that we can all enjoy its benefits for our overall well-being.
