Health benefits of dietary prebiotics

Prebiotics have been an integral part of normal human diet for many centuaries. Prebiotics are essential specific colonic nutrients that have the potential to considerably influence whole body’s physiology and consequently health and wellbeing. Prebiotics affect specifically and selectively the indigenous beneficial bacteria. Prebiotics are able to alter the colonic microbiota toward a healthier composition by increasing for example, numbers of saccharolytic species while reducing putrefactive microorganisms. Some prebiotics are added to foods to improve food quality characteristics such as mouth feel and other textural aspects. Prebiotics have been used as low calorie fat replacers. Human milk can be considered as the original prebiotic for gut microflora management in breast –fed infants.

Definition

Prebiotic is a non-digestible food ingredient which beneficially affects the host by selectively stimulating the growth of and/ or activating the metabolism of one (or more) health promoting bacteria in the intestinal tract (Gibson and Roberfroid 1995).

A dietary probiotic is a selectively fermented ingredient that allows specific changes, in the composition and/or activity of the gastrointestinal microbiota, thus confers upon host wellbeing and health (Gibson et al 2004).

Prebiotic concept

A prebiotic is a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health. In order for s food ingredient to be classified as a prebiotic it must

1)  Be neither hydrolysed nor absorbed in the upper part of the gastrointestinal tract;
2) Be a selective substrate for one or a limited number of beneficial bacteria commensal to the colon, which are stimulated to grow and/or are metabolically activated;
3) Consequently, be able to alter the colonic flora in favour of a healthier composition and
4) Induce luminal or systemic effects that are beneficial to the host health.

Synbiotics –probiotics may be used in conjunction with specific substrates (prebiotics) for growth (e.g. a fructooligosaccharide in conjunction with a Bifidobacterial strain or lactitol in conjunction with a lactobacillus organism). This combination could improve the survival of the probiotic organism in the host because its specific substrate is readily available for its fermentation.

Recognized prebiotics

The common prebiotics in use include fructo-oligosaccharides (FOS), galcto-oligosacchardes (GOS),soy-oligosaccharides (SOS), inulins, lactulose and pyredextrins,. The majority of studies carried out to date have focused on inulin, FOS and GOS (Macfarlane et al 2008).

Emergent prebiotics

Emergent prebiotics include genti-oligosaccharides,gluco-oligosaccharides, isomalto-oligosaccharides(IMO),lactosucrose, levans, pectic-oligosaccharides,resistant starch, sugar alcohols and xylo-oligisaccharides (XOS).

Prebiotic mechanism of action

1. Produce short chain fatty acids during fermentation of probiotic carbohydrates.
2. Increase fecal weight and mildly reduce luminal colon pH.
3. Stimulate the growth of carbohydrate fermenting bacteria.
4. Lower the concentration putrefactive, toxic, mutagenic or genotoxic substances.
5. Decrease the concentration of nitrogenous end-products and reductive enzymes.
6. The Bifidobacteria and lactobacilli exhibit low b-glucuronidase and nitroreductase activity.
7. Enhance immunity and modulate mucin production.

Prebiotic food sources

Fructooligosaccharide (FOS) is a naturally occurring prebiotic compound found in many edible sources such as artichokes, bananas, honey, onion, garlic, barley and others. Another prebiotic compound inulin is naturally found in chicory roots, wheat, onion, garlic, bananas, fruits and vegetables.Examples of food sources rich in prebiotics are whole grain, honey, banana, garlic,onion,tomato, leek, artichoke and chicory.

Prebiotic characteristics

1.       Non-digestible or partially digestible

2.       Non-absorbable in the small intestine

3.       Well fermented by beneficial bacteria in the gut and

4.       Selective stimulation of growth and activity of intestinal bacteria.

Metabolic fate of prebiotics

Inulin and oligofructose are not hydrolysed in the mouth, stomach and small intestine. In the large intestine, they undergo complete anaerobic fermentation by bacteria. They do not contribute any calories. They are completely fermented in the colon, so inulin is not excreted in the stool.

Prebiotics and dietary fibres

Prebiotics and dietary fibres are not digested by human digestive enzymes, but prebiotics are fermented selectively in the colon and exert their health effects via colonic microbiota. Dietary fibre on the other hand may not be fermented at all and exert health effects in other ways for example improved bowel function.

Colonic microbial system

The colonic microbial system consists of wide range of bacterial species, a variety of different metabolic niches, bacterial habitats and interrelationships. In general intestinal bacteria may be divided into species that exert either harmful or beneficial effects on the host. Pathogenic or harmful effects include diarrhea, infections, liver damage, carcinogenesis and intestinal putrefaction; health promoting effects may be caused by the inhibition of growth of harmful bacteria, stimulation of immune functions, lowering of gas distension problems, improved digestion and absorption of essential nutrients and synthesis of vitamins.

Health promoting functions of Bifidobacteria

Bifidobacterium is a major group of saccharolytic bacteria in the colon and constitutes up to 25% of the total population in the gut of adult and 95% in the new borns (Kawerze et al 1981). Bifidobacteria produce strong acids as metabolic end products (acetate, lactate), lower the pH and may exert an antibacterial effect. Bifidobacteria produce vitamins largely of the B – group. Bifidobacteria produce certain immunomodulators, which promote immunological attack on malignant cells. Bifidobacteria have been used to restore the normal intestinal flora during antibiotic therapy (Korshunov et al 1985). 

Health benefits of  dietary prebiotics

1)      Increase the absorption of dietary minerals such as calcium, magnesium and iron.

2)      Reduce the risk of colon cancer.

3)      Reduce cholesterol and blood lipids.

4)      Prevent gastrointestinal tract infections.

5)      Increase growth of Bifidobacteria, which has following beneficial effects:

i)        produces nutrients such as B-group vitamins and folic acid.

ii)       Produces digestive enzymes.

iii)     Reduces food intolerance by utilizing residual nutrients from the upper gut.

iv)     Improves nutrient management.

v)      Reduces liver toxins i.e. blood amines and ammonia, by using them as fuels.

vi)     Competitive elimination of pathogenic microorganisms.

Summary

Prebiotics are non-digestible food ingredients. They are selectively fermented by intestinal bacteria ( e.g. lactobacilli, Bifidobacteria). Potential health benefits of prebiotics include increased bioavailability of dietary minerals and reduced risks of various diseases such as cancer, intestinal infections, cardiovascular disorders, obesity and diabetes. Prebiotics are naturally available in several foods such as whole grains, onion, garlic, bananas, fruits and vegetables.
                            Prebiotics are effective for gut health