Prebiotic foods carry the essential dietary fibers that can be fermented by the commensal bacteria in the large colon. These complex carbohydrates based fiber chains are the desired and required foodstuffs for our gut microbiota. Prebiotics nourish and help the growth of diverse friendly bacteria and support our digestive health. Prebiotic foods act as a carbon source for primary and secondary fermentation pathways in the colon.
Definition of Prebiotics
As per International Scientific Association for Prebiotics and Probiotics (ISAPP) Prebiotics are, “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.”
Recent definitions have included their immense benefits to our mental health, hence defining Prebiotics as, “a non-digestible compound that, through its metabolization by microorganisms in the gut, modulates composition and/or activity of the gut microbiota, thus conferring a beneficial physiologic effect on the host”.
Characteristics of Prebiotic Foods
Prebiotics have five important characteristics as:
- Not digested by upper gastrointestinal (GI) tract.
- Reach large colon and fermented by certain microbiota.
- Produce helpful metabolites, reduce colonic pH and reduce the production of harmful nitrous compounds.
- Have a good effect of GI disorders and other body diseases.
- Not affected by food processing.
Best Prebiotic Food Sources
Fruit, vegetables, cereals, and other edible plants are natural sources of carbohydrates constituting prebiotics. Some of them are:
- Green Banana, Banana Flower, and Banana Stem
- Bamboo shoots
- Artichokes, Turnips, Beetroot, Radish
- All yams including Elephant Yam – Jimikand
- Garlic, Onions, Leeks, Ginger, Chicory, Spring Onions, Asparagus
- Ladies Finger
- Oats, linseed, barley, and wheat.
- Psyllium Husk
- Potato with skin, Sweet Potato
- Lentils, Chick-peas, kidney-beans, lima beans, mung beans, green peas, black gram
- Guar Beans
Some artificially produced Prebiotics are:
- Lactulose. Lactulose constitutes a significant part of produced oligosaccharides (40%).
Types of Prebiotic Foods
They can be divided into eight categories of Prebiotics:
Beta-glucans are water-soluble substance founds in cereals with varieties in chemical structure. They are found in mushrooms, algae, seaweed, and other marine plants. Oats, Barley, Wheat, Quinoa, and Millets are the best sources of beta-glucans.
Fructans (FOS) and Inulin
These are various substances including inulin, fructooligosaccharides (FOSs) and oligofructose. They have good Bifigenic effects (positive effects on the growth of friendly bacteria Bifidobacteriareside). Some examples
They are composed of 2-10 galactose molecules and 1 glucose molecule. They influence the GI bacteria in different manners. Some examples are Lentils, Chick-peas, kidney-beans, lima beans, mung beans, black gram, green peas.
They are composed of glucose monomers linked together in different ways to give: isomaltose, isomaltotriose, and panose. IMO is naturally found only in few food sources and most are commercially produced. They are also partially digested in the colon. Artificially produced IMO should be taken within the limit (5-10g per day). High doses as 30 gram per day can cause GI side-effects and also lead to obesity.
It is gel-like forming galactomannan found in
It is diasaccharide composed of galactose and fructose. It is neither digested nor absorbed but it is so beneficial for GI especially for constipation and prevention of hyperammonemia encephalopathy in patients with severe liver diseases.
Resistant Starches (RSs) and Maltodextrin
RS are broad spectrum of starches which escape digestion in upper GI tract. Resistant maltodextrin is low-viscosity water-soluble dextrin produced through processing of cornstarch.
Xylooligosaccharides contains 2-10 xylose monomers. They are naturally found in dairy products, honey, bamboo shoots, and some fruits, and vegetables. Doses up to 12 gram per day are tolerable for artificially manufactured.
Health Benefits of Prebiotic Foods
Help the growth of microbiota
Lactobacilli have been shown to reduce mucosal inflammation in the GI tract. Also, Lactobacilli play a role in helping digest lactose for lactose-intolerant individuals, relief constipation, improve irritable bowel syndrome (IBS) symptoms, and potentially help to prevent traveler’s diarrhea.
Bifidobacteriareside occurs naturally in the GI tract of healthy human adults and have a strong affinity to ferment oligosaccharides. Also, Bifidobacteriareside is negatively associated with obesity and weight gain. A decrease in Bifidobacteriareside occurs with higher IBS inflammations.
Formation of beneficial metabolites
Production of short chain fatty acids (SCFAs) as acetate, propionate and butyrate is resulted from fermentation of Prebiotics.
Acetate is an important metabolizable energy source for muscles. Propionate and butyrate are negatively associated with ulcerative colitis.
The fermentation of inulin-type fructans produces hippurate. Hippurate is a microbial mammalian co-metabolite which is found to be less in obese and diabetic patients.
Studies show the effect of acid fermentation from Prebiotics by bacteria. This results in enhancing the absorption of calcium from small intestine. Calcium is very important mineral for normal bone growth and prevention of osteoporosis.
Clinical studies conducted to show that: inulin, fructooligosaccharides, galactooligosaccharides, and lactulose can increase calcium uptake from intestine.
Decrease Protein fermentation
Fermentation of protein either from undigestible or endogenous sources, in the absence of carbohydrates is very harmful. This is due to the formation of harmful metabolites as: ammonia and sulfides, indole and phenol compounds.
The fermentation of Prebiotics is beneficial rather than protein fermentation. Studies show that upon taking lactulose (15 gram per day or 2*10 gram per day), it decreases fecal phenol and indole, urinary ammonia , and urinary p-cresol.
Inulin (3*5 gram per day) is found to reduce fecal and urinary ammonia.
Prevents pathogenic bacteria
Prebiotics show to prevent the growth of pathogenic bacteria as E.coli, Salmonella species and Campylobacter species.
A good example for Prebiotics action against pathogenic bacteria is acute diarrhea which is morbid in children. Administration of oral rehydration solution (ORS) alone is not capable to reduce duration and severity of diarrhea.
Studies conducted to evaluate the efficacy of zinc and Prebiotics (FOS and XOS) fortified oral rehydration solution for treatment of diarrhea in children. Results showed that zinc and Prebiotics limit diarrhea duration in patients.
This is due to synergistic activity between zinc and Prebiotics. As, they stimulate water and electrolyte absorption across gut mucosa and inhibiting the pathogens, respectively. Inhibition of pathogens occur due to five mechanisms which are:
- Acidic metabolic end products (acids) that lower the colonic pH below pathogenic bacterial thresholds.
- Competitive effects due to limitations in numbers of colonization sites.
- Antagonism through inhibitory peptides (produced by lactic acid bacteria).
- Competition for limited nutrients.
- Enhancement of the immune system.
Decrease permeability to toxins
Epithelial cells covering the mucus membrane of GI tract act as protective barrier. These epithelial cells are covered with mucous which secreted by goblet cells for further protection from invasion of toxins.
Inflammation in GI tract can cause disturbance in this barrier. This disturbance can lead to passage of Lipopolysaccharides (LPS) which are endotoxins secreted by pathogenic gram negative bacteria.
Studies prove that short chain fatty acids (SCFAs) as acetate, propionate and butyrate, improve the GI barrier. Also, inulin (10gram per day) proved to prevent the passage of LPS in diabetic patients.
Decrease allergy risk
As we mentioned, decrease in both Bifidobacteriareside and lactobacilli are associated with inflammations. Also, they are associated with allergic reactions especially in the first five years of life.
Studies show that addition of FOS and GOS (8 gram per liter in cow milk formula for allergic infants) is beneficial in decreasing eczema in these infants. Also, FOS and GOS in hypo- allergic formulas are beneficial to protect from rhino- conjunctivitis.
Enhance Immune System and Fight Cancer
Metabolites released from the fermentation of Prebiotics have shown to be effective in enhancing our immunity. Acetate shows to have apoptosis effect on tumor cells. Propionate has shown to have anti-inflammatory effect.
Butyrate has shown to be effective in stimulating macrophage, T cells and dendritic cells.
Lower high cholesterol levels and Obesity Prevention
Prebiotic foods have shown to decrease LDL Cholesterol and triglycerides. Studies showed that intake of soy-fortified Prebiotic resulted in greater reductions in low-density lipoprotein cholesterol and
Also, studies have proved that short-chain FOS can induce satiety and thus prevent obesity.
Consumption of Prebiotics is very beneficial. However, high doses can cause flatulence and diarrhea.