What Are Prebiotics?
Prebiotics have been gaining a lot of attention lately due to their impact on the health and diversity of the gut microbiome. Researchers and nutritionists in the mid-1990’s discovered prebiotics as they observed that certain soluble fibers such as inulin, oligofructose and fructo-oligosaccharides caused remarkable changes in the bacterial composition of the colon. Today, the International Scientific Association of Probiotics and Prebiotics (ISAPP) defines “dietary prebiotics” as “a selectively fermented ingredient that results in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health." (1) In other (less scientific) words, prebiotics are fermentable dietary fibers that serve as nutrition for resident gut bacteria resulting in improved digestive, cardiovascular, cognitive, neurological and immune system health.
Health Benefits of Prebiotics
Prebiotics play an important role in human health. They naturally exist in breastmilk (to seed the gut of a newborn baby with healthy microbes) as well as in various plant foods (fructo and galacto-oligosaccharides). The best food sources of prebiotics are asparagus, leeks, garlic, onion, okra, artichokes, barley, rye, peas, beans, and seaweed.
As intestinal bacteria munch on prebiotic fibers, which human digestion is unable to fully break down, they release short-chain fatty acids (SCFAs). SCFAs include lactate, acetate, butyrate, and propionate which increase the acidity of the colon (lower the colonic Ph), improve intestinal absorption, and modulate the innate immune system to better defend the host against pathogenic organisms.
Short-chain fatty acids are also beneficial for improving the integrity of the gut lining. Butyrate in particular serves as a substrate (food) for colonocytes (cells lining the large intestine) and is involved in the development of the intestinal epithelium: a one-cell thick protection layer separating the intestinal lumen from the rest of your body preventing foreign substances like microbes, undigested food particles, and toxic molecules from entering the circulation. (2),(7)
The short-chain fatty acids produced from the digestion of prebiotic fibers by intestinal bacteria are molecules small enough to diffuse through the gut lining and enter the bloodstream exerting their protective, anti-inflammatory effects not only on the gastrointestinal system but on other organ systems in the body as well including the central nervous system, immune system, and cardiovascular system. (4),(5),(6)
The health benefits associated with eating a diet high in prebiotic fibers are diverse and can include improved digestive and cognitive function as well immune modulation through increased production of immunoglobulins and sIgA (secretory IgA is a gut-specific immune function marker), increased production of immuno‐regulatory cytokines, and a reduction in pro‐inflammatory cytokines.(2),(7)
Types of Prebiotics
Prebiotics are a type of fermentable soluble fiber. Although not all prebiotics are considered carbohydrates, the majority of them are a subset of carbohydrate groups called oligosaccharide carbohydrates (OSCs). The most known and researched prebiotics are fructo-oligosaccharides (FOS), including inulin or oligofructose, galacto-oligosaccharides (GOS), and trans-galacto-oligosaccharides (TOS). (1),(2)
Non-carbohydrate types of prebiotics are flavonols, a type of plant pigments with anti-oxidant properties found in fruits and vegetables, tea, and raw cacao beans.
Resistant Starch {RS}
Resistant starch is another type of prebiotic, which has been shown to stimulate the growth of butyrate producing bacteria in the colon. As mentioned earlier, butyrate is a type of short-chain fatty acid that preserves the integrity of the intestinal mucosa and has anti-inflammatory properties. RS includes the portion of starch that can resist digestion by human pancreatic amylase (enzyme responsible for breaking down carbohydrates) in the small intestine and thus, reach the colon intact.(3) RS is found in many plant foods, including grains, root vegetables (especially potatoes), legumes, seeds, and some nuts. Fruits like bananas and mangoes are also a great source of resistant starch in their unripe or green state when the simple sugars (fructose, sucrose and glucose) are very low while RS constitutes the largest portion of the fruit (50-80%).
Consumption of resistant starch has been associated with improved insulin resistance and post-prandial glucose response (minimizing blood glucose spikes), which may have beneficial implications in the management of diabetes, and is associated with a decrease in the levels of cholesterol and triglycerides. Other benefits of RS consumption are "increased fecal bulk and bowel movement frequency, prevention of constipation and hemorrhoids, decreased production of toxic and mutagenic compounds, lower colonic pH, and ammonia levels."(3)
A Word of Caution
Since human enzymes cannot break down prebiotic fibers, they are transported to the colon and fermented by gut bacteria. The observed side effects of prebiotic consumption or supplementation are mostly due to increased levels of fermentation and resulting osmotic pressure. There are occasionally negative symptoms of consuming prebiotics, the most commonly reported being diarrhea, bloating, cramping, and stomach pain. (7)
The chain length of prebiotic fibers is important to consider since the shorter chains like inulin may produce more side effects due to their rapid fermentation in the proximal colon. On the other hand, longer chains (FOS and GOS) are fermented more slowly and later in the distal colon.
Dose also plays a role considering that studies show a daily dose of 2.5–10 g of prebiotics is required to observe beneficial effects on human health. Even in such therapeutic doses, prebiotic supplementation may lead to some adverse effects in more sensitive individuals suffering from some level of microbial imbalance or dysbiosis. (7)
Certain dietary approaches like the low FODMAP diet (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) or the SCD (Specific Carbohydrate Diet) restricting some naturally occurring prebiotics from the diet, have proven to be effective in improving symptoms in irritable bowel syndrome (IBS) and small intestinal bacterial overgrowth (SIBO). However, such diets lower the numbers of key gut microbiota (specifically Bifidobateria) with unknown impact on long-term health. (7)
With this in mind, it is important to use caution when recommending an increased dietary intake or supplementation with prebiotic fibers, especially in individuals with gut dysbiosis, SIBO and increased GI inflammation. However, the long-term restriction of fermentable fibers may have negative consequences for the health and diversity of the gut microbiome, potentially exacerbating the condition down the road. Careful evaluation and systematic reintroduction of fiber and prebiotic rich foods is strongly recommended with the application of carbohydrate restricted diets.
The Synergistic Effect of Pre and Probiotics
Probiotics are beneficial bacterial strains known to increase the diversity of the gut microbiome and improve various markers of health including digestive, cognitive and immune system function. The most commonly researched and used probiotic strains include Lactobacillus rhamnosus, Lactobacillus reuteri, bifidobacteria and certain strains of Lactobacillus casei, Lactobacillus acidophilus-group, Bacillus coagulans. The combination of pre and probiotics is referred to as "synbiotic", representing the synergistic relationship between these two substances.(8)
Many probiotic products sold today contain added prebiotics to enhance the activity and viability of the bacterial strains in the gut. "The stimulation of probiotics with prebiotics results in the modulation of the metabolic activity in the intestine with the maintenance of the intestinal biostructure, development of beneficial microflora, and inhibition of potential pathogens present in the gastrointestinal tract." (9)
More research is needed to better understand the synergistic effect of pre and probiotics on human health and their long-term benefits. Until then, it is probably safe to say that a diet abundant in prebiotic fibers and fermented, probiotic-rich foods is your best bet when looking to optimize your intestinal and overall health. After all, we know that our hunter-gatherer predecessors consumed over 100 g of prebiotic fiber daily. In contrast, our modern diet consists of an unimpressive 15g of fiber on average. Needless to say, we can and should make some improvements on that front before we reach for the supplements.
Here is a delicious recipe to get you started. Please leave me a comment below to let me know how you liked it.
Be Well ♥
Homemade Kimchi Recipe {Rich in Fiber, Pre and Probiotics}
INGREDIENTS:
1 medium size head napa cabbage (organic if possible)
1 bunch of green onions, chopped
4-5 cloves of garlic, peeled
Korean red pepper flakes (1-5 tablespoons depending on how much spice you can handle)
2-3 Tbsp Celtic or sea salt
1-2 Tbsp of sugar (I personally use about a spoon to get the fermentation process going)
3 carrots or 1 cup Daikon radish, peeled and thinly shredded
1 teaspoon grated peeled fresh ginger
Filtered water
DIRECTIONS:
Cut the cabbage lengthwise through the stem into quarters.
Place chopped cabbage in a large bowl and add the salt. Using your hands, massage the salt into the cabbage and between the leaves until it starts to soften a bit. Add water to cover the cabbage. Cover the bowl with a plate or towel and let stand for about 2 hours or until cabbage is wilted.
Rinse the cabbage under cold water a few times so it is not overly salty. You can taste a piece to make sure. Set aside to drain.
Meanwhile, make the Kimchi paste. Add red pepper flakes, garlic, ginger, sugar, and water to a food processor and mix into a smooth paste.
Squeeze any remaining water from the cabbage and add to the spice paste. Add the scallions and shredded carrots and massage everything well with your hands. You can wear gloves here to avoid stains and smells from seeping into your skin.
Pack the kimchi into a 1-quart jar. Press down on the kimchi until the juice or brine rises to cover the vegetables, leaving at least 1 inch of space at the top. Seal the jar.
Let the jar sit at cool room temperature, out of direct sunlight, for 1 to 5 days. You may see bubbles inside the jar and brine may seep out of the lid.
Check the kimchi daily, opening the jar and pressing down on the cabbage with a clean finger or spoon to keep the leaves submerged under the juices. This will help to releases gases produced during fermentation. Taste a little at this point, too! When the kimchi tastes ripe enough for your liking, transfer the jar to the refrigerator.
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