What is fiber?

Fiber consists of indigestible components of plant-based foods, most of which are made up of complex carbohydrates. Although they provide no energy, they are essential for healthy digestion, stable blood sugar levels, and the cardiovascular system.

The name “fiber” comes from a time when people thought these substances were meaningless to the body - today, however, we know that they play a central role in health, metabolism, and the gut microbiome.

Fiber is found exclusively in plant-based foods, particularly in whole-grain products, legumes, vegetables, fruits, nuts, and seeds.

Types of fiber

Fiber is divided into two main groups depending on how it behaves in water and what function it performs in the body:

1. Soluble fiber:

  • They form a gel-like substance in the digestive tract.

  • They slow digestion and ensure a steady rise in blood sugar.

  • They lower cholesterol levels by binding bile acids.

  • They serve as food for gut bacteria (prebiotic).

  • Examples: pectin (in apples), beta-glucans (in oats and barley), inulin (in chicory and Jerusalem artichokes), guar, oligofructose.

2. Insoluble fiber:

  • They swell in the intestines and promote intestinal activity and stool transit.

  • They support cleansing of the digestive system and help prevent constipation.

  • Examples: cellulose, hemicellulose, lignin (e.g., in whole grains, bran, nuts, and vegetables).

The combination of both types of fiber ensures optimal digestive and metabolic health.

How does fiber work in the body?

1. Digestive support:
Fiber binds water, increases stool volume, and stimulates intestinal movement (peristalsis). This softens the stool and regulates digestion - both in cases of constipation and sluggish bowel activity.

2. Blood sugar regulation:
By slowing carbohydrate absorption, fiber prevents rapid blood sugar spikes after eating. This relieves the burden on the pancreas and helps prevent insulin resistance and diabetes.

3. Cholesterol-lowering:
Soluble fiber binds bile acids, which contain cholesterol. As a result, more cholesterol is excreted through the intestines, contributing to lowering LDL cholesterol.

4. Supporting the gut microbiome (prebiotic effect):
Fiber serves as food for the “good” gut bacteria. Their breakdown produces short-chain fatty acids such as butyric acid, propionic acid, and acetic acid, which have anti-inflammatory effects, protect the intestinal lining, and strengthen the immune system.

5. Satiety and weight regulation:
Because dietary fiber binds water and swells, it increases the feeling of satiety. This helps prevent cravingsand reduce calorie intake without sacrificing volume in the diet.

6. Detoxification and gut health:
Insoluble fiber speeds up intestinal transit and thus reduces the contact time of potentially harmful substances with the intestinal lining.

Benefits of dietary fiber

  • Promote healthy digestion and prevent constipation

  • Stabilize blood sugar and insulin levels

  • Support cholesterol breakdown and heart health

  • Promote satiety and help with weight regulation

  • Strengthen the gut flora and immune system

  • Protect the intestinal lining and have anti-inflammatory effects

  • Contribute to a lower risk of cardiovascular disease, type 2 diabetes, and colorectal cancer

Recommended daily intake

The German Nutrition Society (DGE) recommends for adults:

  • At least 30 g of dietary fiber per day
    This corresponds, for example, to:

  • 3 servings of vegetables

  • 2 servings of fruit

  • 2–3 slices of whole-grain bread or one serving of whole-grain pasta/rice

  • 1 handful of nuts or legumes

Possible side effects

Increasing fiber intake too quickly can initially lead to bloating or a feeling of fullness. Therefore, intake should be increased gradually and combined with sufficient fluids (at least 1.5–2 liters per day).

Very high amounts without adequate fluid intake can slightly inhibit the absorption of certain minerals (e.g., iron, zinc, calcium) - however, this is harmless with a normal diet.

Conclusion

Dietary fiber is essential for a healthy diet. It supports digestion, regulates blood sugar and cholesterol, supports the microbiome, and provides long-lasting satiety. A fiber-rich diet - rich in whole-grain products, vegetables, fruit, legumes, and nuts - strengthens the gut, heart, and metabolism and makes a decisive contribution to long-term well-being and health.

Sources

  1. German Nutrition Society (DGE). (2020): Dietary fiber intake - DGE recommendations.

  2. Slavin JL. (2013): Fiber and prebiotics: mechanisms and health benefits. Nutrients, 5(4), 1417–1435.

  3. Anderson JW, et al. (2009): Health benefits of dietary fiber. Nutr Rev, 67(4), 188–205.

  4. Reynolds A, et al. (2019): Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet, 393(10170), 434–445.