Prebiotics manipulate the intestinal microbiota whether ingested intentionally (as in a supplement) or along with a regular meal (food-sourced). Rather than supplying new bacteria, prebiotics are nondigestible food ingredients that selectively stimulate desirable bacteria already present in the host’s intestinal tract. “Back in the day” no one worried about eating enough prebiotics or probiotics. The food they were forced to survive on was overflowing with prebiotic fiber as well as covered with invisible life and grit. As a result, their guts were full of the beneficial strains of bacteria we need to thrive.
“A prebiotic is a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health."
These are the foods that our ancestors ate without thinking, but now require considerable effort to find or prepare in a way that maximizes these qualities. Gone are the days when our main staples were good for us and our gut bugs. There are presently only a handful of whole-food substances that are thought to possess these qualities and can be classified as “prebiotics,” although new foods are being explored and the list continues to grow. In 2007, only inulin fit the bill, now the list includes:
- Human Milk Oligosaccharides - the carbohydrates found in human breast milk, a human’s first (and most important) taste of prebiotics.
- Resistant Starch - the most common storage carbohydrate of plants. Found in tubers, roots, green bananas, green plantains, legumes, peas, oats, nuts, carrots, maize, sedge nutlets, and grains.
- Oligosaccharides - (inulin, fructo-oligosaccharides, galacto-oligosaccharides, xylo-oligosaccharides) the second most common storage carbohydrate of plants (chicory, onion, leek, dandelion, endive, asparagus, green bananas, legumes, lentils, oats, rice bran, maize, grains).
- Non-Starch Polysaccharides (NSP): (found in small amounts in nature)
- Arabinogalactan - a storage carbohydrate of trees and many plants (carrots, radish, black gram beans, pear, maize, red wine, tomatoes, sorghum, coconut meat)
- Glucomannan - found in the cell walls of certain plant roots and wood, also a component of bacterial and yeast membrane. Konjac roots contain 40% by dry weight and are a great source of glucomannan
- β-Glucans - found in oats, barley, whole grains, shiitake, oyster, maitake, mushrooms, dates, yeast
- Pectin - found in avocados, berries, citrus, fruits, vegetables
- Gums and mucilages - found in seed extracts (guar, locust bean), tree exudates (gum acacia, algal polysaccharides (alginates, agar, carrageenan), psyllium
There are also a few man-made prebiotics derived from plants and animals:
And there are a few other items found in whole foods in trace amounts that have prebiotic or prebiotic-extending properties:
- Galacto Oligosaccharides - derived from cow’s milk to simulate human breast milk for infant formula.
- Fructo Oligosaccharides - separated from natural inulin, used in sweeteners.
- Mannan Oligosaccharides - made from yeast cells, approved only for animals.
And there are a few other items found in whole foods in trace amounts that have prebiotic or prebiotic-extending properties:
- Polyphenols and Flavonoids - found in many places in trace amounts; colorful plants, dark chocolate, seaweed, and mushrooms.
- Glycoprotein and glycolipids - Found in raw meat, raw blood, cartilage, gelatin, collagen, chondroitin, and animal cells.
- Chitin and chitosan - found in fungi, yeasts, insects, worms.
When we eat food that is 100% digested in our stomach and small intestines, such as sugar and flour, there is nothing left for the trillions of hungry passengers in our large intestine. Don’t get us wrong! They will eat—they are survivors after all—or go extinct. The problem is, the populations of beneficial microbes, the ones who do the most for us, will be quickly taken over and crowded out by the mongrels that are only out for themselves. The pH of the gut will change, the muscles that support the gut will weaken, the gut lining itself will become permeable and allow toxins, enteric organisms and undigested food to pass into the bloodstream. Since 70% of the immune system is in the gut, it will crumble over time. Eventually you will have the gut that modern man devised with his massive brain—the dyspeptic, inflamed gut of a technologically advanced society that feeds its people cheaply and efficiently. In our age of plenty, food barons profit at the expense of the consumer’s health.
In our modern era, the definition of prebiotics has been subject of much debate and a cause of confusion for consumers. Since the dawn of Man, this is the first time we’ve had to rely on others to tell us what we need to eat to ensure healthy populations of gut bugs. Up until fairly recently, the food that was available to us contained everything we needed to thrive as a species, now, with modern processing, artificial colors and flavors, and advertisements convincing us to eat tasty treats, it’s impossible to let our second-brain guide us to the best choices.
Gut microbes as a whole can eat a wide variety of foods, both from plant and animal origin, and will readily feed on us when there is nothing suitable provided. In fact, bacteria that feed on us, or more specifically the mucus that we secrete, are a normal part of a healthy gut flora. However, when these mucus degraders become dominant or the mucous layer too thin, the colon degrades into a state of fragility. We have all sorts of gut bugs that eat all sorts of foods, but the concept behind prebiotics is that a specific type of food feeds a specific type of microbe—microbes that convey exceptional health benefits to us. These bacteria are normally thought to be of the Lactobacillus and Bifidobacteria types as they are the producers of short-chain fatty acids that provide fuel to the specialized cells which line our colons (colonocytes) and in turn ensure that the parts of our immune system which reside in our gut are kept healthy. A well-fed gut with robust populations of Lactobacillus and Bifidobacteria is considered a very healthy gut. There are still hundreds of other species present in the gut, healthy or otherwise. Some of these can be harmful or helpful depending on the status of the gut. Prebiotics and the gut bugs they stimulate help keep the other bacteria in their ‘friendly states’ and the entire gut ecosystem benefits.
Prebiotics are complete nutrition for our gut bugs. We need prebiotics so that our guts will be filled with beneficial microbes, namely Bifidobacteria, Lactobacillus, Bacteroides, and Clostridium clusters IV and XIVa. These types of microbes are the main gut bugs associated with above average gut health. They produce chemicals we cannot get from food we eat that our body relies on for survival.
Bifidobacteria and Lactobacillus are odd in their eating habits. In one study, 55 different species of bifidobacteria or human and animal origin (basically ALL known species) were fed inulin. Only 5 of the bifidobacteria species could eat the inulin, and then, not very efficiently. Lactobacillus is similar, it feeds mainly on plant matter and in fact would rather take up residence in the small intestine where it has access to more food and oxygen. The presence of these two bacteria types are more an indication that the prebiotics are feeding a thriving colony of other beneficial bacteria, known as keystone species, that do the primary degrading of prebiotics. When the entire ecosystem is thriving, Bifidobacteria and Lactobacillus will also thrive.
It was found in several studies that more than 25% of healthy human subjects could not break down prebiotic fibers.
In a study was done using inulin. They narrowed it down even further finding that people fell into three main groups:
- Not Sensitive Group - 71% of healthy adults (able to eat 30g+)
- Sensitive Group - 25% of adults (able to eat 10-30g)
- Very Sensitive Group - 4% (not able to eat even 10g)
Sensitivity, by the way, generally refers to people who experience excessive flatulence, discomfort, bloating, or pain after ingestion of inulin or RS. What these researchers were missing is the piece of the puzzle filled in by gut bugs. The folks who cannot tolerate RS or inulin are missing key microbes that degrade the prebiotic fiber so that the Bifidobacteria, Lactobacillus, Bacteroides and Clostridia can thrive.
Low fiber diets (ie. very low carbohydrate diets, low FODMAP diets, Standard American Diet, etc) may help create ‘empty’ guts that have severe reductions in the populations of intestinal inhabitants that are the heavy butyrate factories which keep the colonocytes vibrant and maintain the gut free of pathogens. The long-term effects of these diets may have subtle and adverse effects on downstream health due to the profound effects on the microbiota.
There are many different fiber types, not all prebiotic, not all plant-based, but important nonetheless. Foods such as whole grains, vegetables, fruit, seeds, nuts, legumes, and tubers are considered high fiber foods, but they contain much more than fiber. Until recently, more attention was given to the fiber content of a food, but this proved largely ineffective at reversing modern disease. While the fiber aspect of a food is important, the prebiotic effect is more important. Fiber is a spectrum. The US Department of Agriculture (USDA) would love to have us all believe that the fiber spectrum is a dynamic duo consisting of soluble and insoluble fibers. These designations have done nothing for the health of the nation and gave food manufacturers carte blanche to fool consumers into buying ‘healthy’ muffins filled with cotton batting and sawdust.
Eating one type of fiber without a matrix of synergistically-acting viscous, gel-forming, soluble and insoluble fibers is not equally effective as what is found in whole, untainted food. It’s the combination of prebiotic and non-prebiotic fiber (mainly cellulose) that make a gut truly happy. Unfortunately most western sources of fiber come from high gluten hybridized wheat, breakfast cereals with wood pulp cellulose, rancid vegetable oil soaked French fries or potato chips, and fungicide-laced salad bars. The great majority of inulin (78%) is gained from wheat, not vegetables or richer sources.
As we showed you in the last chapter, our ancestors exuberantly ate loads of prebiotic fiber. It’s estimated they may have consumed upwards of 135 grams of fiber per day...contrast that with modern man’s intake of less than 5 grams per day. Our thoughtful government has recommended we eat 25 grams of “fiber” daily and in doing so ensured we get virtually none of the natural and food-based prebiotic fibers we so desperately need. The average intake of prebiotic fibers is less than 5 grams per day in most of the affluent societies of the modern world. Most of our fiber intake is boxed and packaged refined grains, potato and corn snack foods with minuscule portions coming from fruits, legumes, and nuts. Missing from our diet is the food with natural prebiotics that stimulate the gut to good health, these prebiotic foods are good for our guts and good for us. These are the foods our forefathers relied heavily upon—uncooked and cooked, retrograded starches and plant fibers with their micronutrients and tagalong microbes which support a healthy gut and immune system.
“The remarkable properties of dietary NSPs are water dispersibility, viscosity effect, bulk, and fermentability into short chain fatty acids (SCFAs). These features may lead to diminished risk of serious diet related diseases which are major problems in Western countries and are emerging in developing countries with greater affluence. These conditions include coronary heart disease, colorectal cancer, inflammatory bowel disease, breast cancer, tumor formation, mineral related abnormalities, and disordered laxation. Insoluble NSPs (cellulose and hemicellulose) are effective laxatives whereas soluble NSPs (especially mixed-link β-glucans) lower plasma cholesterol levels and help to normalize blood glucose and insulin levels, making these kinds of polysaccharides a part of dietary plans to treat cardiovascular diseases and Type 2 diabetes.”
Sorely missing from our diet are the prebiotics—the stuff that feeds the elite gut bugs that convey the greatest health benefits. The two main sources of prebiotic fiber (inulin and resistant starch) come from plants that stockpile food inside their roots, tubers, and leaves. The first prebiotic we are exposed to, the sugars in breast milk, are generally the last prebiotics any modern human eats in any meaningful quantity.
Inulin is found in fairly high amounts in foods such as leeks, asparagus, chicory, Jerusalem artichokes, garlic, onions, and soybeans. Although the amount of inulin-type fructooligosaccharides may be small, the fiber acts in synergism with other fibers in plant matter, such as resistant starch or cellulose in the meal to produce higher amounts of butyrate and proliferation of a spectrum of beneficial gut flora, than either would alone. Resistant starches are found in raw tubers, unripe green bananas, as well as cooked and cooled potatoes, tiger nuts (chufa), seeds, rice, maize, grains, legumes, tapioca, cassava and other starchy roots. As you can quickly see, this list of foods is not well represented in most people’s diet. A little effort is required to ensure an adequate intake of fiber and prebiotics.
A well-fed gut, furnished adequate amounts of fiber, is associated with the following health benefits:
- Protection from Cardiovascular Disease
- Type 2 Diabetes and Glycemic Control
- Laxation and Regularity
- Satiety and Appetite Control
- Body Weight
- Reduced Risk of Cancer
- Gut Barrier Function
- Reduction of Pathogens and Infection Prevention
- Enhanced Short Chain Fatty Acid Production
- Increased Beneficial Gut Flora (Bifidobacteria, Lactobacilli, others)
Commercially prepared prebiotic supplements can be obtained in four ways: Direct extraction, controlled hydrolysis, transglycosylation, and chemical processes. Though prebiotics, in theory, are extractable directly from plants, this method is rarely used in favor of chemically modifying the leftovers from other food manufacturing processes. Most prebiotic supplements are a conglomeration of plant fibers and monosaccharides, polysaccharides, and disaccharides. Further processing removes the mono, poly, and disaccharides, leaving only the oligosaccharides which are dried to a powder and sold as prebiotics.
- Directly extracted - Resistant starch, inulin, soybean oligosaccharides (OS)
- Controlled hydrolysis - Fructooligosaccharides (FOS) from inulin, Xylo OS
- Transglycosylation - FOS from sucrose, GOS from lactose+sucrose
- Chemical Process - Lactitol from hydrogenated lactose
Obviously the question at this point should be: Exactly how much fiber- and prebiotic-rich food do I need to eat? The answer is not entirely clear.
Many studies show that our gut bugs will produce all their magic with about 20-40 grams of prebiotic fiber per day. This amount will provide maximum SCFA production and thriving colonies of gut bugs, but these items are not found in a box of breakfast cereal. You’ll need to eat a combination of prebiotic fiber-rich foods to get it. Since RS is much easier to source in real food, it makes a great substance for bridging the gap in shortfalls of prebiotics. RS also has been shown to be a main player in the production of butyrate, possibly the most important factor in colon health. More on RS later in its own special chapter.
RS and inulin have been extensively studied since the early 1990’s. Inulin was the first proposed prebiotic fiber and RS was studied later. Both have proven to have the exceptional prebiotic properties of providing a fermentable food source for our gut bugs, however, both also proved to be marketing disasters. With > 25% of the general (healthy) population unable to eat prebiotic inulin or RS, the people with the worst guts are the most likely to reach for these foods in an attempt to better themselves only to discover they become extremely gassy, bloated, and uncomfortable. The ones who can digest prebiotics well don’t notice its beneficial actions and discontinue. The manufacturers of inulin supplements have whittled down the recommended dose to a level that 96% of the population can tolerate, and in doing so, created a dose with minimal value to our gut flora.
An easy way to incorporate these ideas is to eat several servings of oligosaccharide-rich vegetables, roots, unripe green bananas, and fruits per day along with several servings of starchy vegetables, such as rice, potatoes, beans or whole (gluten-free) grains prepared in a way to maximize their resistant starch content. Eating in this fashion will provide the nutrients needed for a healthy gut. This is easily obtained by eating a well-balanced diet with ample plant matter and focusing on RS- and inulin-rich foods.
The Prebiotic Curve:
A good rule of thumb is to eat several servings per day of inulin-rich fruit and vegetables, both cooked and raw vegetables, and RS rich foods prepared to maximize their RS content. There are many ways to reach the goal of 20-40g/day, the charts below show some of the higher-dividend food choices.
Green Banana, 1 large
Cowpea, White Lupin
Lentils, Chickpeas, Hummus
Pinto beans (cooked/cooled)
Mungbean glass noodles
Tiger Nut, raw
Pistachio, Cashew, Chestnut
When a human being assembles the necessary ingredients and places them in a vessel suitable for fermentation, then oversees the progress, making corrections along the way until the process is complete, and finally eats the fermented food, it is a display of two brains acting for the common good of the superorganism. Our ability to create a new food from existing, somewhat edible food, simply through the act of farming wild microbes, is testament to the influence of our gut microbes.
Man was eating fermented foods before man was even man. The first animal that ever ate fruit found lying on the ground was eating fermented fruit. The first animal that ate a bite of rotten meat was eating fermented meat. It probably doesn’t take long for an animal to realize that it can get very sick eating foods that smell a certain way, and it probably didn’t take our ancestors very long to realize that eating certain smelly fruits didn’t make them sick, but made them giddy, giggly, lightheaded, and walk funny. It also probably didn’t take them long to learn that eating certain smelly foods didn’t make them sick, and in fact, made them feel better. Imagine the first Inuit who ate “stink head”...he must have been some kind of HONGRY. Also, then, imagine the first poor soul who drank a bowl full of honey and water that had been left in the sun too long...
Soon, though, our big brains harnessed this smelly, rotten food and turned it into something that improved the flavor of dishes, increased the nutritional value of the food, made food last longer, made us sleepy, horny, and even cured us of disease. Scientists have been deconstructing these uses of fermented foods to unlock their secrets and found fermentation significantly alters the original food in a way that produces new chemicals such as lactoferrin, unique flavonoids, and bioactive peptides. They’ve also discovered the main player in fermentation known as Lactobacillus.
It’s hard to say when fermentation was put to meaningful use, but ancient artifacts from over 10,000 years ago display evidence that fermentation of fruit, rice, and honey was common practice at that time. With the rise in agriculture, fermentation was not just limited to fruits and alcohol production, but dairy, grains, and meat were being fermented as a means of preservation and taste enhancement.
Though rarely used except as minor side-dishes in affluent Westernized societies, many parts of the world still rely on fermented foods for a large portion of their food intake. These populations have been studied and the health benefits they derive from fermented foods contribute immensely to the health of those who partake of fermented foods.
Research shows that fermentation magnifies the benefits of many foods and herbs, making chemicals in these foods bioavailable and active and also creating new vitamins, especially of the “B” variety. We’ve also learned much about how fermented foods and their microbial passengers interact with our own gut bugs and influence our microbiota in positive ways. Notice, if you will, that the main players in fermentation are also the ones we called “probiotic,” this is not a coincidence! The main products of fermentation are alcohol, lactic acid, and acetic acid. These acids lower the pH of the food being fermented to a level that is hostile to most pathogens. It makes sense that a microbe that can keep pathogens out of a jar of cabbage could also keep pathogens out of our intestines. But more than that, these same microbes, both living and dead, play an important role in our immune system—just the mere sniff of a dead probiotic is enough to train our second-brain to recognize this as an ally and not an enemy. Additionally, many new live bacteria are introduced into a healthy microbiome and take up residence when there is space.
During the first several million years our human ancestors fermented most of the food they ate in their guts. As we became more organized, herding animals for their milk and meat, we became more sophisticated. We learned to ferment foods before we ate them. We discovered that soured milk lasted longer. Cheese, with its added salt, lasted even longer and tasted very interesting. We figured out that clay pots were wonderful vessels in which to ferment vegetables, fish, shrimp, honey and grape juice. Then somehow along the way, some of us decided that gut bacteria were superfluous. We decided that Hippocrates was an ancient ignorant when he claimed that all illness begins in the gut. Bacteria became the enemy, not the friend. We thought we beat them but instead we met our Waterloo: without our good bacteria, the bad ones defeat us. We need to relearn what our ancestors practised. By learning to prepare and eat human-appropriate foods, whether fermented in a crock or in the gut, we pay homage to the millions of years of evolution by the synergism between the human animal and its gut bacteria. In this way we take big steps in regaining the healthful vigor we deserve.
Over the past 10,000 years our diet has changed drastically. Most of us went from being hunter-gatherers to agriculturalists and pastoralists and then to consumers of high-fat, high-calorie, highly-processed foods. The changes we’ve seen in the past 100 years have been the most damaging to our health as a species. A few simple tweaks and we can once again enjoy the benefits of health as conveyed by our intestinal microbes. We can live as humans are meant to live—a focus on prebiotics and probiotics is paramount to this transformation. Fewer of us are eating correctly to support thriving colonies of beneficial microbes. The increasing prevalence of chronic diseases over the past 10,000 years can be attributed in part to a lack of probiotics and prebiotic rich foods.
Special thanks to Dr. Grace Liu, PHARMD, for inspiration, studies, editing, and contributions to this article.
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