If you’ve heard of probiotics, you are probably familiar with the importance of gut health, but have you heard of pre-biotics? Prebiotics are a form of carbohydrate and dietary fiber found in plant foods that help to feed the beneficial bacteria in your gut, and incorporating more prebiotic foods in your diet can have a positive impact on your health.
What are prebiotics?
Prebiotics are a group of nutrients that help to stimulate the growth or activity of beneficial bacteria in the body (1). Trillions of live microorganisms inhibit the human gut, known as the gut microbiota, which has a major impact on the health of the human body.
In simple terms, a prebiotic is a form of food for the good bacteria in the gut microbiome. Prebiotics are not digested by humans, rather, they are acted on by gut microbes, which produce a variety of beneficial compounds, such as short-chain fatty acids (2).
According to the International Association for Probiotics and Prebiotics, a prebiotic is defined as “a substrate that is selectively utilized by host microorganisms conferring a health benefit” (3). In more technical terms, for a compound to be classified as a prebiotic, it must meet the following criteria (1):
- be resistant to acidic pH of the stomach, cannot be hydrolyzed by mammalian enzymes, and also should not be absorbed in the gastrointestinal tract,
- be fermented by intestinal microbiota, and
- the growth and/or activity of the intestinal bacteria can be selectively stimulated by this compound and this process improves host’s health.
Prebiotics, along with probiotics, such as yogurt, sauerkraut, and kombucha, help to balance the bacteria in our gut. A healthy gut microbiome has been shown to improve mineral absorption, modulate the immune system, improve satiety, thereby supporting weight loss, reduce the risk of inflammatory bowel syndrome, promote metabolic health (insulin resistance, healthy blood lipids), and reduce the risk of allergy (3, 4, 5).
Types of Prebiotics
There are many types of prebiotics, the majority of them are a subset of carbohydrate groups, mostly oligosaccharide carbohydrates, and include (1):
- Fructans: Includes inulin and fructo-oligosaccharide (FOS) or oligofructose.
- Galacto-Oligosaccharides (GOS): Product of lactose extension, which can greatly stimulate Bifidobacteria and Lactobacilli.
- Starch and Glucose-Derived Oligosaccharides: Includes resistant starch; a form of starch that is resistant to upper gut digestion.
- Pectic Oligosaccharides (POS): Oligosaccharides are originated from a polysaccharide known as pectin.
While prebiotics are generally found in carbohydrate-based foods, there are other compounds, such as cocoa-derived flavanols, which have been shown to stimulate lactic acid bacteria and classify them as prebiotics (6).
What are prebiotic foods?
Prebiotics naturally exists in a variety of carbohydrate-based foods, including:
| Vegetables | Asparagus, garlic, Jerusalem artichoke, leeks, onion, tomatoes, sugar beets |
| Fruits | Bananas, apples, watermelon, grapefruit, pomegranate, dried fruits, nectarines |
| Legumes | Chickpeas, lentils, beans |
| Grains | Oats, barley, rye, wheat |
| Roots | Chicory root, dandelion root, elecampane root |
| Other | Honey, cocoa powder, seaweed, milk, breast milk |
Although many prebiotics are forms of dietary fiber, not all dietary fiber is prebiotic. Dietary fiber can be soluble or insoluble and is naturally present in whole grains, legumes, fruits, and vegetables, however, not all of these fibers have prebiotic benefits.
Unlike dietary fiber, which has a recommended daily allowance (RDA) of 25-35 grams of total fiber per day, or 14g of fiber per 1,000 calories, at present, there are no official dietary recommendations or RDA for prebiotics. Most prebiotics for the gut require an oral dose of at least 3 grams per day or more to confer a benefits, so it is recommended to consume at least 5 grams of FOS and GOS daily, which includes food sources of prebiotics (3).
Best Food Sources of Prebiotics
Here is a list of 15 of the best prebiotic foods.
1. Apples
Whether you like gala, Honeycrisp, or Granny Smith, apples are a good source of prebiotic fiber, as well as pectin, a form of soluble fiber (7). Apples are also a good source of antioxidants and vitamin C, not to mention they are inexpensive, convenient, and versatile. Apples can be consumed on their own, sliced into salads, cooked into savory dishes, or baked into muffins and oatmeal.
2. Asparagus
Asparagus is a great food to help boost your prebiotic fiber intake and add some greens to your diet at the same time. Asparagus is a good source of inulin; a form of fructo-oligosaccharide, which may improve digestive health, relieve constipation, promote weight loss, and help control diabetes (8, 9). Asparagus can be steamed, boiled, grilled, roasted, blanched, and added to salads, or cooked into risotto, soups, and stews.
3. Bananas
Bananas, specifically slightly unripe bananas, are high in resistant starch and contain a small amount of inulin (10). Bananas are also a source of complex and simple carbohydrates, including natural sugars, making them great for satisfying a sweet tooth while benefiting your gut health at the same time. Underripe, green bananas can be made into fried green bananas or added to a savory stew.
4. Barley
Barley is a whole grain rich in beta-glucan; a prebiotic fiber that improves the growth rate of probiotic bacteria. Beta-glucan has also been shown to help lower total and LDL cholesterol and reduce the risk of cardiovascular disease (11, 12). Barley can be cooked into soups, and stews, made into bread, or used in salads.
5. Beans and Lentils
Legumes, including beans, lentils, and chickpeas, have natural prebiotic properties as contain oligosaccharides, polyphenols, and isoflavones, and are particularly good sources of resistant starch (13). Legumes are good sources of complex carbohydrates, fiber, protein, and micronutrients, and make a wonderful addition to a healthy diet. They can be cooked into soup, stew, or chili, consumed cold in salads, or consumed on their own as a simple side dish.
6. Chicory Root
Chicory root comes from a flowering plant that is part of the dandelion family and is high in inulin and prebiotic fiber. Chicory root has a distinct coffee-like flavor and has historically been used as natural medicine, however, is now commonly used in teas, protein and fiber bars, and low-sugar cereals.
7. Dandelion Greens
Dandelion greens are a highly nutritious plant loaded with vitamins, minerals, and prebiotic fiber. Dandelion greens have been shown to improve digestion, improve immune health, and reduce inflammation and cholesterol levels (14). Dandelion greens are a versatile and inexpensive ingredient that can be sautéed, steamed, and added to salads, soups, or stews similar to kale, spinach, collards, or other dark leafy greens.
8. Garlic
Garlic is an herb with a long tradition of medicinal use well known for its antioxidant, antimicrobial, and anti-inflammatory properties. Garlic is also a source of prebiotic fiber that promotes the growth of the beneficial bacteria Bifidobacteria in the gut (15). Garlic can be added to marinades, dressings, meats, veggies, soups, stews, casseroles, pasta, and one-pot meals, or consumed in conjunction with other prebiotic food for an extra boost.
9. Jerusalem Artichoke
Jerusalem artichokes, also known as the sunchokes or earth apples, are an inulin-rich source of dietary fiber and have been shown to increase the friendly bacteria in your colon (16). Jerusalem artichokes are tubers that are similar to root vegetables in texture and appearance and, once cooked, act quite similar to potatoes, making them ideal for boiling or roasting.
10. Leeks
Leeks are a good source of prebiotic fiber, vitamin K and antioxidants called flavonoids (17). Leeks are from the same plant family as garlic and onion, the Allium genus, and therefore offer similar health benefits. With their distinct mild and sweet flavors, leeks are a wonderful substitute for onions or can be added to soups, stews, pasta, quiches, or sautéed on their own to create a simple side dish.
11. Mushrooms
Most edible varieties of mushrooms are rich in chitin, hemicellulose, β and α-glucans, mannans, xylans, and galactans that act as prebiotics (18). Mushrooms are also a source of B vitamins, selenium, copper, potassium, and fiber, and can be an abundant source of vitamin D. Mushrooms are highly versatile ingredients that can be enjoyed raw or cooked in salads, pasta, soup, stews, or roasted or sautéed as a simple side dish.
12. Oats
Oats are well known for being a healthy whole grain and are also a good source of prebiotic fiber thanks to their high level of beta-glucan and some resistant starch. The high level of fiber and nutrients found in oats has been shown to help lower cholesterol levels, improve blood sugar control, slow digestion, and control appetite (19, 20). Whether you are using steel-cut, rolled, or quick-cooking, oats are a versatile and inexpensive ingredient that can be used for a bowl of oatmeal, baked oatmeal, overnight oats, or added to your favorite baked goods.
13. Onions
Onions are another versatile and inexpensive ingredient that is rich and nutrients and prebiotic fiber. Similar to garlic, onions are rich in inulin and fructo-oligosaccharides which aid digestion and boost beneficial gut bacteria. Onions also contain antioxidants and compounds that help to fight inflammation, decrease triglycerides, and reduce cholesterol levels, all of which may help fight heart disease (21, 22, 23). Onions are a flavourful addition to the base of any soup, stew, sauce, marinade, or dressing.
14. Rye
Rye is a whole grain, commonly used for bread and cereals that is rich in prebiotic fiber. Rye grains, the bran in particular, are a good source of beta-glucan (similar to oats) and are also a source of fructo-oligosaccharides and arabinoxylan, which were shown to promote the growth of specific probiotic bacteria in the gut (24, 25). Additionally, when rye flour is fermented for use in sourdough bread, rye was shown to help feed the microbes in the gut (26). Rye has a dark color and nutty taste and is commonly used in bread and crackers.
15. Wheat
Wheat, especially wheat bran, is a good source of prebiotic fiber. The fiber in wheat bran, which is made of the prebiotic arabinoxylan-oligosaccharides (AXOS), has been shown to boost beneficial bacteria in the gut (27). Consuming wheat bran or whole grain wheat products, such as whole grain bread or whole grain pasta, is another good way to increase consumption of prebiotic fiber.
Other prebiotic-rich foods include cacao, flaxseed, burdock root, jicama root, yacon root, and seaweed.
Other Sources of Prebiotics
In addition to food sources, prebiotics are sometimes added to processed foods such as yogurt, bread, breakfast cereals, sauces and soups, sports drinks, granola bars, and snack bars. Prebiotics can also be found in supplement form in prebiotic supplements, as part of a probiotic supplement, or in fiber supplements containing inulin.
The Bottom Line
Prebiotic foods are forms of carbohydrates and fiber, including fructans, galacto-oligosaccharides, and resistant starch, that help to stimulate the growth or activity of beneficial bacteria in the gut. Consuming a wide variety of prebiotic foods, such as onions, garlic, leeks, bananas, and asparagus, can help to support overall health.
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