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Nutrition > Food Facts

Supporting the intestinal flora with prebiotics

Dr. med. André Sommer

Dr. med. André Sommer

Millions of bacteria occupy the mucous membranes of our bodies. There are many different strains of bacteria in the digestive tract, especially in the large intestine. This is also called the intestinal flora or the microbiome. The bacteria affect the health of the person in whose gut they live: Certain species can cause disease while others support the immune system. The composition of the microbiome can be influenced by nutrition. So-called prebiotics support the beneficial intestinal bacteria.

What are prebiotics?

Prebiotics are certain components of food. Prebiotics include long-chain carbohydrates. These are sugar chains of different lengths. Human digestive enzymes cannot break down these sugars. They enter the colon undigested and serve as food for the bacteria. Prebiotics are characterized by the fact that they can only be digested by certain health-promoting types of bacteria, but not by other bacteria. It is believed that prebiotics support the activity and growth of useful strains of bacteria and thus improve health.

According to this definition, prebiotics include:

  • Fructooligosaccharides (FOS): Multiple sugar from fructose
  • Galactooligosaccharides (GOS): Polysaccharides
  • Lactulose: Double sugar, produced in small quantities when milk is heated
  • Further oligosaccharides such as inulin, raffinose, stachyose: Mixture of multiple sugars

However, not all foods advertised as prebiotics actually meet these criteria. Prebiotics have to reach the large intestine in order to be effective. To do this, they should not be decomposed by stomach acid or absorbed by the small intestine. In addition, intestinal bacteria have to ferment the carbohydrates.

What foods contain prebiotics?

Prebiotic plant substances are naturally contained in these foods:

  • Artichoke
  • Bananas
  • Beans
  • Chicory
  • Peas
  • Cereals (low)
  • Garlic
  • Leeks
  • Onions

Since many of these foods lead to flatulence, you should only gradually add them to your menu. So your digestive tract slowly gets used to the indigestible substances.

Keep in mind: Not everyone can tolerate prebiotic foods

Although prebiotics generally have a positive effect on the healthy intestinal bacteria, not all people tolerate prebiotic foods. This is because the fermentation of the prebiotics (= the breakdown of the prebiotics by bacteria) produces gases that can lead to uncomfortable flatulence.

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What are the health benefits of prebiotics?

The benefits of inulin, fructooligosaccharides and galactooligosaccharides have been most researched. They mainly influence the growth of health-promoting bifidobacteria.

Possible effects of prebiotics on the intestinal bacteria Health effects
Stimulate the carbohydrate metabolism of healthy intestinal bacteria:
  • Growth
  • More short chain fatty acids
  • Gas formation through fermentation
Short-chain fatty acids can provide energy for cells in the intestinal mucosa

Gas formation can lead to uncomfortable flatulence and abdominal pain

Promote growth of bifidobacteria and lactobacilli Greater resistance to invading pathogens
Do not affect blood sugar levels (non-glycemic) Are well tolerated by people with high blood sugar (diabetes mellitus)
Increase the absorption of magnesium and calcium Can prevent osteoporosis
Reduce the formation of blood lipids (cholesterol, triglycerides, VLDL) in the liver Can protect against calcification of the coronary arteries

Where can you buy prebiotics?

Prebiotics are plant-based components of foods. They are found in vegetables such as beans, artichokes and onions, among others.

In the meantime, prebiotics are also manufactured and marketed industrially. Inulin powder is available as a dietary supplement online or in pharmacies. With a balanced diet, this addition is usually not necessary.

Watch out!

Prebiotics are easily confused with probiotics. Probiotics are living microorganisms that have a health-promoting effect on the body.

What prebiotics can I take on a low-FODMAP diet?

There are also certain restrictions to be observed with prebiotics. Because even if prebiotics can promote health, they trigger complaints in some people. If you have irritable bowel syndrome, prebiotic foods are often unsuitable because of their flatulence.

In the treatment of irritable bowel syndrome, a low-FODMAP Diet help (Fermentable Oligosaccharide, Disaccharide, Monosaccharides “and” Polyols). Most prebiotics are FODMAP-rich foods that should be avoided during this diet. During the so-called elimination phase, you have to do without some prebiotics. Appropriate foods are then gradually reintroduced in the testing phase (provocation phase). So you may not have to do without permanently.

But there are also some low-FODMAP prebiotics that you can also eat in the elimination phase. The following table shows which prebiotics you can and cannot eat during the low-FODMAP diet.

Suitable Not suitable
  • Chicory leaves (less than a cup)
  • Fennel bulb (half a cup)
  • Green portion of leek and spring onions
  • 20 grams of beetroot
  • Half a cob of corn
  • Half a cup of canned lenses
  • A cup of red cabbage
  • Bananas, kiwi, rhubarb, a teaspoon of cranberries, half a pomegranate
  • Oatmeal
  • Products made from wheat (couscous, pasta, bread, gnocchi), barley, rice
  • Artichokes, peas, leeks, corn, garlic, beetroot, asparagus, onions
  • Pomegranate, grapefruit, persimmon, nectarines, peaches, dried fruit, watermelon
  • Cashews, pistachios
  • Foods to which inulin has been added (see list of ingredients on the packaging!)

Gibson, G. R., & Roberfroid, M. B. (1995). Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. The Journal of nutrition, 125(6), 1401-1412. Downloaded on 03.09.2018 from:

Macfarlane, G. T., & Cummings, J. H. (1999). Probiotics and prebiotics: can regulating the activities of intestinal bacteria benefit health?. Western journal of medicine, 171(3), 187. Downloaded on 03.09.2018 from:

Unger, S. (1999). Die Bedeutung von Pro-und Präbiotika in der Ernährung. Journal für Ernährungsmedizin, 1(1), 22-29. Downloaded on 03.09.2018 from:

Roberfroid, M. (2007). Prebiotics: the concept revisited. The Journal of nutrition, 137(3), 830S-837S. Downloaded on 03.09.2018 from:

Schrezenmeir, J., & de Vrese, M. (2001). Probiotics, prebiotics, and synbiotics—approaching a definition–. The American journal of clinical nutrition, 73(2), 361s-364s. Downloaded on 03.09.2018 from:

Dr. med. André Sommer

Dr. med. André Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara Care.

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