Written by Azadeh Khiabani, Ph.D. in Food Biotechnology
What are prebiotics?
The concept of prebiotics was first proposed in 1995 by Gibson and Roberfroid in one of their scientific publications. The current scientific definition of prebiotics was presented by a group of experts in microbiology, nutrition and clinical research in 2016, by the International Scientific Association for Probiotics and Prebiotics (ISAPP). Today, prebiotics are defined as “a substrate that is selectively utilized by host microorganisms conferring a health benefit”. The most significant changes occur in the activity of the microbial flora of the digestive tract. Thus, this concept includes three essential parts: a substance, a beneficial physiological effect, and a microbiota-mediated mechanism.
Many efforts have been made to use prebiotics as functional food compounds in order to improve the intestinal microbial flora and ultimately increase the health of the host. Prebiotics are non-digestible food compounds that are selectively fermented by some bacteria and cause changes in the composition, growth and activity of digestive bacteria in the large intestine, mainly lactobacilli and bifidobacteria, which bring many benefits to the health of the host.
The function of prebiotics
To understand the role and function of prebiotics, you must first understand what probiotics are, as they are often confused with each other. Probiotics are live microorganisms that have been isolated from the human gut and have beneficial effects on the body when consumed in sufficient amounts. Probiotics can be found in dietary supplements and fermented foods.
Prebiotics act as a food source for intestinal microorganisms, so they must bypass the digestive process and reach the colon. Intestinal microorganisms metabolize and ferment prebiotics to survive. This process of metabolism and fermentation is beneficial for intestinal health because it helps the body in different ways by producing beneficial metabolites.
The substances that are used as substrates for the growth of intestinal bacteria are generally introduced through the diet and include foods that are not absorbed in the upper parts of the digestive system. These foods include indigestible oligosaccharides, dietary fibers, and proteins that reach the large intestine undigested. Some peptides, proteins and some special lipids can also be considered as prebiotics, but indigestible carbohydrates are the most reliable prebiotics. Prebiotics may exist naturally or be synthesized.
Most dietary fibers are considered prebiotics, but scientifically, only a subset of dietary fibers qualify as prebiotics, targeting a limited group of microorganisms (lactobacilli and bifidobacteria) rather than the entire microbial ecosystem to affect the host. When prebiotics are broken down by gut microorganisms, different short-chain fatty acids are created depending on the type of prebiotic. These fatty acids provide energy for colon cells, help produce mucus, and help reduce inflammation and boost immunity. Considering that different microorganisms may use different prebiotics, not all prebiotics have the same effect on the body.
Benefits of prebiotics
Prebiotics offer a wide range of benefits, with ongoing research focusing on their role as food sources for gut microbiota. Some of the benefits of prebiotics include:
- Regulating bowel movements.
- Facilitating the production of neurotransmitters between the gut and brain to stimulate mood changes and other processes.
- Stimulating the body to produce hormones that can increase or suppress appetite.
- Assisting in the absorption of calcium and phosphorus by bones, thereby improving bone density.
- Enhancing the function of the immune system.
- Boosting the body’s anti-inflammatory response system.
- Increasing the number of beneficial bacteria while reducing the number of pathogenic bacteria.
Prebiotic foods
Prebiotic foods typically contain a specific type of fiber called soluble, fermentable fiber. The method of cooking also plays a role in determining the amount and type of prebiotics present. While there are various types of prebiotics, three of the most common can be found in resistant starches, inulin, and pectin.
- Resistant starch can be found in boiled and cooled potatoes, green bananas, barley, oats, rice, beans and legumes.
- Inulin is present in asparagus, burdock root, chicory root, dandelion greens, garlic, artichoke, leek, onion, and soy.
- Food’s high in pectin include apples, apricots, carrots, green beans, peaches, raspberries, tomatoes, and potatoes.
When is the best time to take prebiotics?
It is recommended to gradually introduce prebiotics into your diet so that your body’s microbiota can adjust to them. Since the body operates on a circadian rhythm, intestinal microorganisms are more active during the day, so it is advisable not to consume prebiotics late at night.
Individuals with digestive issues like irritable bowel syndrome (IBS) may struggle to digest certain prebiotics, particularly those found in stone fruits such as peaches, mangoes, and cherries. When you consume fruits and vegetables, you not only receive fiber, vitamins, and minerals, but also likely some prebiotics.
The recommended dose of prebiotics
Currently, there are no official dietary recommendations for the adequate intake or recommended daily intake of prebiotics in healthy individuals. The number of prebiotics needed for benefits to intestinal health is at least 3 grams per day. The recommended daily amount of fiber is 28 grams per day based on a 2000 kcal per day diet.
For more information, please refer to the articles on (Fermented foods), (Synbiotics), (Postbiotics), and (Functional Foods).
