“Prebiotic” is a term that shouldn’t be confused with “probiotic,” although the two are indeed connected.
A probiotic is a food that introduces helpful bacteria to the digestive tract, while a prebiotic is a food that feeds the bacteria that already live in your gut.
Prebiotic foods play an important role in maintaining a healthy body. Understanding the importance of prebiotics means knowing how they interact with your intestinal bacteria, or “gut flora,” and what benefits your gut flora provide.
What is a Prebiotic?
A prebiotic is a type of soluble fiber. Fibers fall into either the insoluble or soluble category. Insoluble fiber cannot be digested or dissolved in liquid and passes through the body—this is the type responsible for fiber’s link to the volume and passage of bowel movements. Soluble fiber also cannot be digested. But since it dissolves in liquid, it’s the type that your intestinal bacteria can absorb. They do this by eagerly breaking down prebiotics into short-chain fatty acids that they then use for fuel.
There are many types of prebiotics. The most studied are inulin and fructooligosaccharides (FOS). Pectin, incidentally, also has prebiotic properties, but inulin and FOS are the big ones with the most known benefits to the approximately 500 different species of bacteria living in your gut.
Our Little Friends
Your intestines and colon are riddled with bacteria that prebiotics feed and support. The exact benefits of each type of bacteria aren’t all identified yet, but some specifics have been figured out. Many bacteria of the Bifidobacterium strain provide services like modulating immune responses and adjusting the PH-level of the intestinal tract, which can make it a hostile environment for other bacterial invaders. The Lactobacillus family can ease inflammation and has suspected-but-unconfirmed anti-carcinogenic properties.
More generally, gut flora perform a number of useful functions. These include:
- Limiting the hunger-causing hormone ghrelin after you eat a meal high in carbohydrates
- Breaking down any undigested carbohydrates, allowing your body to absorb them
- Producing vitamins K and B12
- Promoting bone strength and density by helping the body take in calcium and magnesium
- Protecting the digestive tract by providing a “barrier effect,” essentially crowding out harmful bacteria like the colitis-causing, Clostridium difficile
- Having some unconfirmed associations with reduced allergies in infants and children
- Increasing immune factors in the colon wall
- Reducing flatulence (great for the bean-lovers out there)
Strictly speaking, gut flora are not essential to the human body and people can survive without them. Doing so, however, definitely comes with inconveniences. To get an idea of how much we benefit from our gut flora, consider an experiment where mice were raised without any intestinal bacteria. The mice with sterile guts needed to eat 30% more carbohydrates just to get the same energy as mice that had normal bacteria levels.
Prebiotic Foods List
Now that you know more about how your intestine’s trillion-strong army helps out, the benefits of foods high in prebiotics should be clearer. As mentioned earlier, inulin and FOS have some of the better understood health benefits. So, let’s focus on them.
Inulin and FOS are found in bananas, oats, berries, garlic, onions, asparagus, and various root vegetables. The recommended amount is around six grams (0.21 oz) of prebiotics per day. However, the average American diet only contains about a third of this—mostly from wheat or onion sources.
For reference, here are the average inulin and FOS levels for 100 g of various prebiotic foods:
- Chicory root: 41.6 g inulin and 22.9 g FOS
- Jerusalem artichoke: 18.0 g inulin and 13.5 g FOS
- Dandelion greens: 13.5 g inulin and 10.8 g FOS
- Garlic: 12.5 g inulin and 5.0 g FOS
- Leeks: 6.5 g inulin and 5.2 g FOS
- Asparagus: 2.5 g inulin and 2.5 g FOS
- Wheat bran: 2.5 g inulin and 2.5 g FOS
- Baked wheat flour: 2.4 g inulin and 2.4 g FOS
- Banana: 0.5 g inulin and 0.5 g FOS
Except for wheat flour, these are all values for the foods in raw form. Cooking causes a loss of about 10-20% of a food’s prebiotic content. A simple way to improve your intake is to grab a banana on the way to work or maybe mix some more raw veggies into your salad.
Jerusalem artichokes and chicory root have some of the highest concentrations of inulin and FOS, so eating them is definitely recommended. Jerusalem artichokes (which are neither from Jerusalem nor artichokes) are a tuber of the sunflower plant and best used as a potato substitute. Coffee lovers out there will be excited to know that chicory powder can be used as a substitute for the popular caffeinated beverage. Get your morning pick-me-up and some healthy gut flora all in one cup!
Are There Any Downsides of Prebiotic Foods?
Prebiotics aren’t for everyone. While most people enjoy a healthy relationship with their gut flora, others aren’t as lucky. Those suffering from Small Intestinal Bacterial Overgrowth (SIBO) experience an overabundance of gut flora. Feeding them with prebiotic foods can amplify problems like constipation or diarrhea (sometimes both!), gas and bloating, and in extreme cases, malnutrition or dangerous weight loss.
Similar but more temporary symptoms can occur if those with regular gut flora amounts overdose on prebiotics. Fortunately, it takes over 30 g (1.06 oz) to reach these inadvisable levels, so there is plenty of safe wiggle room for those who want to go over the recommended daily amount.
It’s important to keep in mind that prebiotics don’t only benefit your gut flora. If you’re already playing host to an unpleasant intestinal invader like a member of the Klebsiella family, then prebiotics could end up feeding them as well.
Do You Need a Supplement?
As important as they are, there’s a good chance you won’t need to take any extra prebiotic supplements to get your six grams per day. A synthetic form of inulin is used in a surprisingly large amount of processed foods since it can serve as a substitute for sugar, fat, or flour. Synthetic inulin can be found in many dairy products, sports drinks, cereals, soups, or sauces. Check your ingredient labels and do some quick mental math to see if you’re already taking enough. If you’re not, and can’t get the six grams from diet alterations, then a supplement may be right for you.
If you do decide to take supplements, be careful to start small and work your way up to your ideal dose. Gut flora don’t like sudden changes in diet, so giving them a dramatic boost in food could end up causing some short-term digestion problems.
Under-Recognized, but Important
It’s a shame so little is known about our gut flora, since the little bits we do know are fascinating. These guys are a private army that keeps our digestive tracks running smoothly and our bodies ticking along healthily and happily. But an army only marches on a full stomach. So, be sure to stay on top of your daily prebiotic foods intake to keep them well fed!
“Good Bacteria Trigger Proteins to Protect the Gut.” EurekAlert! Accessed April 8, 2015.
Moshfegh, Alanna J., James E. Friday, Joseph P. Goldman, and Jaspreet K. Chug Ahuja. “Presence of Inulin and Oligofructose in the Diets of Americans.” The Journal of Nutrition 129, no. 7 (1999): 1407-411.
Gibson, Glenn R., and Robert A. Rastall. “When We Eat, Which Bacteria Should We Be Feeding?” ASM News 70, no. 5 (2004): 224-31.
Macfarlane, S., Macfarlane, G. T. and Cummings, J. H. (2006), Review article: prebiotics in the gastrointestinal tract. Alimentary Pharmacology & Therapeutics, 24: 701–714. doi: 10.1111/j.1365-2036.2006.03042.x
Björkstén, B., E. Sepp, K. Julge, T. Voor, and M. Mikelsaar. “Allergy Development and the Intestinal Microflora during the First Year of Life.” Journal of Allergy and Clinical Immunology 108, no. 4 (2001): 516-20.
Steinhoff U. “Who controls the crowd? New findings and old questions about the intestinal microflora.” Immunology Letters 99, no. 1. 2005; 99:12–16. doi: 10.1016/j.imlet.2004.12.013.