What is fiber?

Fiber is the indigestible component of plant-based foods, consisting largely of complex carbohydrates. Although it provides no energy, it is essential for healthy digestion, stable blood sugar levels, and the cardiovascular system.

The term “fiber” dates back to a time when these substances were thought to be of no importance to the body. Today, however, we know that they play a central role in health, metabolism, and gut flora.

Fiber is found exclusively in plant-based foods, especially whole grains, legumes, vegetables, fruit, nuts, and seeds.

Types of fiber

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

1. Soluble fiber:

• Form a gel-like substance in the digestive tract.

• Slow digestion and promote a steady rise in blood sugar.

• Lower cholesterol levels by binding bile acids.

• Serve as food for gut bacteria (prebiotic).

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

2. Insoluble fiber:

• Absorb water and expand in the intestines, promoting bowel activity and stool movement.

• 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 supports optimal digestive and metabolic health.

How does fiber work in the body?

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

2. Regulates blood sugar:
By slowing carbohydrate absorption, fiber prevents rapid blood sugar spikes after meals. This reduces the strain on the pancreas and helps prevent insulin resistance and diabetes.

3. Lowers cholesterol:
Soluble fiber binds bile acids, which contain cholesterol. This increases the amount of cholesterol excreted through the intestines, helping to lower LDL cholesterol.

4. Promotes gut flora (prebiotic effect):
Fiber serves as food for the “good” gut bacteria. When broken down, it produces short-chain fatty acids such as butyric acid, propionic acid, and acetic acid, which reduce inflammation, protect the intestinal lining, and strengthen the immune system.

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

6. Detoxification and gut health:
Insoluble fiber speeds up intestinal transit, thereby reducing 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 reduction and heart health

• Promote satiety and help regulate weight

• 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 fiber per day
  For example, this corresponds to:

• 3 servings of vegetables

• 2 servings of fruit

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

• 1 handful of nuts or legumes

Possible side effects

Increasing fiber intake too quickly can initially cause 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)—but this is harmless with a normal diet.

Conclusion

Dietary fiber is essential for a healthy diet. It promotes digestion, regulates blood sugar and cholesterol, supports the microbiome, and provides long-lasting satiety. A fiber-rich diet—rich in whole grains, 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.