What is dietary fiber?

Dietary fiber consists of indigestible components of plant-based foods, largely composed of complex carbohydrates . Although it provides no energy, it is essential for healthy digestion, stable blood sugar levels, and the cardiovascular system .

The name "dietary fiber" comes from a time when these substances were thought to be meaningless to the body – today, however, we know that they play a central role in health, metabolism and gut flora .

Dietary fiber is found exclusively in plant-based foods, especially whole grain products, legumes, vegetables, fruits, nuts and seeds .

Types of dietary fiber

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

1. Soluble dietary fiber:

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

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

  • They lower cholesterol levels because they bind bile acids.

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

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

2. Insoluble dietary fiber:

  • They swell in the intestines and promote bowel activity and stool transport .

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

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

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

How do dietary fibers affect the body?

1. Aids digestion:
Dietary 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. Blood sugar regulating:
By slowing down carbohydrate absorption, dietary fiber prevents rapid spikes in blood sugar after meals. 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. This leads to increased cholesterol excretion through the intestines, which helps to lower LDL cholesterol .

4. Promotion of intestinal flora (prebiotic effect):
Dietary fiber serves as food for the "good" gut bacteria. During its breakdown, short-chain fatty acids such as butyric acid, propionic acid, and acetic acid are produced, 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 to avoid cravings and reduce calorie intake without sacrificing volume in the diet.

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

Benefits of dietary fiber

  • They promote healthy digestion and prevent constipation.

  • Stabilize blood sugar and insulin levels

  • Support cholesterol reduction and heart health

  • They have a satiating effect and help with weight regulation.

  • Strengthen the gut flora and the immune system

  • They protect the intestinal lining and have an anti-inflammatory effect.

  • They contribute to a lower risk of cardiovascular disease, type 2 diabetes, and colorectal cancer.

Recommended daily intake

The German Nutrition Society (DGE) recommends the following for adults:

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

  • 3 portions of vegetables

  • 2 portions of fruit

  • 2-3 slices of wholemeal bread or a portion of wholemeal 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 slowly and combined with sufficient fluid intake (at least 1.5–2 liters per day).

Very high amounts without sufficient 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 promotes digestion, regulates blood sugar and cholesterol, supports the microbiome, and ensures long-lasting satiety. A fiber-rich diet—rich in whole grains, vegetables, fruits, legumes, and nuts—strengthens the gut, heart, and metabolism and makes a crucial 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.