Are you ready for some mind-boggling numbers? Intestinal bacteria account for approximately 95 per cent of the total number of cells in your entire body, which means there are around 100—700 trillion of this beneficial bacteria located in your intestines, all working together to keep you healthy. Although probiotics, which is the scientific understanding of foods that boost these bacteria, is still in its infancy, our understanding of it is moving ahead rapidly.
Probiotics are foods or products containing a defined single or mixed culture of live microbes that exert beneficial effects on health by altering the intestinal “microflora”, the type of bacteria you have in your digestive system. Probiotics have also been called “friendly bacteria”, or “good bacteria”, and have been consumed for hundreds of years in the belief they exert health benefits, even if at the time people were not sure why the benefits arose. Modern research has demonstrated the beneficial effects that probiotic bacteria, as normal residents in the intestinal tract, offer not only in promoting health but also in treating and preventing disease.
As probiotics is a popular topic of research, scientific knowledge of these potential health benefits is increasing. Some probiotic cultures appear to modulate the immune system, improve lactose intolerance, resolve some bacterial and viral diarrhoeal diseases, reduce symptoms associated with inflammatory bowel disease, lower blood cholesterol and even protect against some cancers.
The bacterial community that naturally resides within the human gastrointestinal tract is complex. It contributes to human health and its disruption can affect the balance of your entire system. Probiotic supplementation can contribute to disease prevention by maintaining a balanced gastrointestinal system that, in turn, leads to beneficial health effects throughout your body.
The ecosystem within
Within your digestive system is a complex ecosystem comprising approximately 400–500 different species of bacteria and, of these, 30–50 species predominate. This ecosystem is referred to as the intestinal microflora and these bacteria make a significant contribution to not only the healthy functioning of the digestive system but also various other metabolic activities including cholesterol metabolism, hormone metabolism and immune function.
Various factors such as poor diet, alcohol intake, excessive stress and the use of certain medications may contribute to changes in the makeup of this ecosystem. Such shifts in the balance of intestinal flora have long been considered to have significant health effects.
At birth, the human gastrointestinal tract is sterile and is then colonised by bacteria, mainly through feeding. The bacteria that colonise the human intestinal tract soon become an essential and functional part of the body. The microflora of the adult human is found primarily in the colon (large intestine) and parts of the small intestine.
The main groups of bacteria that colonise your digestive tract include bacteroides, eubacteria, bifidobacteria and lactobacilli. There is a mutually beneficial relationship that exists between these bacteria and the human body. The human provides both an environment for the bacteria to inhabit and also food, which the bacteria may utilise for their subsequent metabolism and growth.
Non-digestible carbohydrates (eg dietary fibres) that escape digestion in the upper digestive tract are a food source for the microflora. Through fermentation of these carbohydrates, the bacteria produce certain materials that the human body can subsequently use in the course of its own metabolism.
The bacterial production line
Fermentation of carbohydrates by the microflora results in the production of short-chain fatty acids, such as acetic, proprionic and butyric acids. Short-chain fatty acids are important sources of energy for the cells of the large intestine and may also promote the growth and development of intestinal cells. These same short-chain fatty acids may also provide small amounts of energy to muscle, kidney, heart and brain, and provide anti-inflammatory activity. Research indicates that short-chain fatty acids and butyric acid specifically may potentially play a role in the prevention of cancer.
Bacteria in the intestines also produce some vitamins including vitamins B12, K and biotin, which can be absorbed by the intestines and supply part of the dietary requirement.
Immune effects
With about 80 per cent of the immune system found within the gastrointestinal system, it’s not surprising that the microflora may also provide a large contribution to immune function. The microflora may contribute to protection and repair of the intestinal lining by signalling immune cells that repair is required. Some bacteria have actually been found to stimulate the production of intestinal mucus, which forms a protective barrier as part of the gut lining. Other species may be involved in the maturation and development of the immune system.
The bacteria may also play a role in the regulation of inflammation through blocking certain inflammatory chemicals and stimulating the production of anti-inflammatory substances. It has been stated that the immune cells resident in the gut do not simply tolerate the bacteria, but may, in fact, rely on them.
The microflora may also support immune function by providing a defence against potentially detrimental and disease-causing (pathogenic) bacteria. They stop the growth and colonisation of pathogenic bacteria by producing antimicrobial substances and also by competing with them for nutrients and binding sites on the intestinal wall. If pathogenic bacteria are unable to adhere to the intestinal wall, they have much less chance of proliferating within the intestines or causing infection.
Unbalanced equals unwell
The intestinal microflora also plays a role in the metabolism of substances such as cholesterol, bile, hormones (eg oestrogen) and certain drugs. With so many beneficial contributions to digestive and immune function, it’s easy to see how an imbalance of the sensitive and complex system of friendly bacteria in the gut may affect health. Shifts in microflora balance may affect the health and integrity of the gastrointestinal system, which in turn may affect digestion and absorption of nutrients and hence overall nutritional status. Immune function, resistance to infection and hormonal imbalance may also be affected.
This imbalance can show up in a number of ways. Symptoms of microflora imbalance include diarrhoea, constipation, bloating, flatulence and abdominal pain. A reduction in beneficial bacteria generally allows an overgrowth of bacteria that may be disease-causing, giving rise to intestinal infections as well as other widespread effects. Many factors may contribute to a shift in the balance of the gastrointestinal tract’s microflora.
Bad news for good bacteria
Poor eating habits
As always, a healthy diet is important in the maintenance of a healthy body and there is no exception when considering microflora balance. Excessive consumption of refined sugars, fatty foods and alcohol may promote the proliferation of detrimental and pathogenic organisms. A diet low in foods containing probiotic bacteria and dietary fibre will also contribute to an unhealthy microflora balance.
Probiotic-containing foods include yoghurt, fermented milk, miso, tempeh and some soy products. Some fibres provide food for the beneficial bacteria and promote the proliferation and potentiation of the actions of beneficial bacteria. These fibres are known as prebiotics and occur in artichoke, the onion family, asparagus, chicory, banana, wheat and non-processed honey.
Physical and emotional stress
Excessive stress is considered a contributing or exacerbating factor in many health complaints. Considering the microflora specifically, it has been noted that the bacteria in the bowel may be particularly sensitive to the effects of stress. Studies show reduced numbers of both bifidobacteria and lactobacilli in adults placed in significantly stressful situations. It has also been proposed that bacterial colonisation of infants may be impacted by stress in the pregnant mother.
Medications
It’s well known that a lot of antibiotics prescribed for infections have the unwanted effect of targeting not only the detrimental infection-causing bacteria, but also beneficial bacteria. A common side-effect of antibiotic use is therefore the overgrowth of opportunistic organisms such as Candida albicans. This organism is naturally found in the body but generally kept in check by the beneficial bacteria such as lactobacilli. Long-term use of the oral contraceptive pill may also affect beneficial bacteria balance.
Probiotic supplementation
Probiotic supplementation is widely used in clinical practice in a bid to promote a healthy balance in intestinal flora. Supplements are generally recommended for people who have a poor diet, are taking certain medications or exhibit digestive symptoms. Probiotic supplements may also be recommended as a therapy for specific conditions.
Problems such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and gastritis are suspected to be associated with microflora imbalance. Certain immune-based conditions such as allergies, eczema and asthma have also been linked with intestinal microflora imbalances. Probiotic supplements generally contain a more concentrated load of viable bacteria than do probiotic foods and therefore may be more effective in producing a therapeutic effect in such conditions.
Various species of bacteria that are known to colonise the human intestines are used in probiotic supplements. The most common ones used are strains of lactobacilli and bifidobacteria — for example lactobacillus acidophilus, l. casei, l. plantarum, l. rhamnosus, l. fermentum and bifidobacteria bifidum, b. lactis, b. infantis. Other bacteria may also be used, including Streptococcus thermophilus.
Streptococcus thermophilus and lactobacillus bulgaricus in fermented milk have been consumed for thousands of years in the belief that they have health benefits. Streptococcus thermophilus has been used to enhance digestion of lactose in those who are lactose intolerant. It does this by producing the enzyme lactase, which breaks down the sugar lactose. A non–disease-causing yeast, Saccharomyces boulardii, has also been used in both animal studies and human clinical trials. This yeast is thought to promote the growth of beneficial bacteria without itself colonising the gastrointestinal tract.
Probiotics as medicine
Conditions improved by probiotics
- Diarrhoea
- Allergies
- Asthma
- Eczema
- Inflammatory bowel disease
- Irritable bowel syndrome
- Helicobacter pylori infection
- Candida albicans infection (thrush)
Diarrhoea
Probiotic micro-organisms such as Lactobacillus rhamnosus GG, L. reuteri, certain strains of L. casei, L. acidophilus and certain bifidobacteria and enterococci (Enterococcus faecium SF68) as well as the probiotic yeast Saccharomyces boulardii have been investigated with regard to their medicinal use, either as single strains or in mixed-culture probiotics.
Bifidobacterium bifidum and Streptococcus thermphilus supplementation has been reported to reduce the occurrence of diarrhoea and rotavirus among infants and young children. Lactobacillus GG has been seen to reduce the incidence of diarrhoea in hospitalised children by 80 per cent and has been used to reduce the incidence of “traveller’s diarrhoea” in adults.
Supplementation with Lactobacillus GG, Lactobacillus acidophilus or bifidobacterium lactis has demonstrated benefit in reducing the incidence of antibiotic associated diarrhoea.
Allergies
Lactobacillus GG may reduce clinical symptoms, intestinal inflammation and mucosal barrier permeability in infants with allergic dermatitis. Allergic conditions are caused by abnormal or exaggerated immune reactions. In conditions such as asthma and eczema, probiotics exert some benefit due to the immune-modulating effects of the bacteria.
Inflammatory bowel disease (IBD)
Inflammatory bowel disease is a complex autoimmune condition in which significant inflammation and ulceration of the bowel may cause myriad symptoms including diarrhoea and pain as well as malabsorption leading to a poor nutritional status. Crohn’s disease and ulcerative colitis are both forms of IBD. The cause and development of these conditions remains unclear. However, the gastrointestinal microflora has been suggested to be involved as well as genetic susceptibility and immune dysregulation.
Probiotic therapy may contribute to reduced frequency of bowel movements, longer remission periods and a reduced risk of relapse. Microorganisms found to be beneficial include Lactobacillus GG, and combination probiotics including L. plantarum, L.casei, L. acidophilus, B. breve, B. longum and Saccharomyces boulardii.
Irritable bowel syndrome (IBS)
Irritable bowel syndrome is a condition associated with symptoms of abdominal pain and discomfort and recurrent bouts of diarrhoea and/or constipation. It has been suggested that those suffering IBS may have a microflora population that differs from that of healthy individuals, leading to abnormal fermentation of food in the gastrointestinal tract. Probiotic supplementation results in significant improvement in overall IBS symptoms.
Helicobacter pylori infection
Infection with Helicobacter pylori is associated with chronic gastritis (inflammation of the stomach) and peptic ulcers. Therapy with antibiotics is generally required for eradication of Helicobacter pylori, but studies show that probiotics may have an inhibitory effect on these infections. Probiotics may therefore have an adjunctive role and hence have a favourable effect on H. pylori infections in humans and reduce the risk of developing disorders associated with high degrees of gastric inflammation.
Candida infection
Candida albicans is a fungus found in the gastrointestinal tract. Its growth is generally kept under control by the various species of the beneficial bacteria in the intestinal microflora. Overgrowth of candida causes symptoms such as thrush and is one of the most common side-effects of prolonged antibiotic use. Although some studies demonstrate benefit with probiotic supplementation in assisting to control the growth of candida, more research is warranted.
Shopping for your bacteria
Probiotic supplements should always contain bacterial strains that are naturally found in humans. As probiotics do not permanently colonise the intestine, they must be taken in sufficient quantities to maintain adequate amounts in the gastrointestinal tract. Hence the delivery vehicle and the concentration of the probioitc are important factors to consider.
Probiotic bacteria need to be in adequate numbers [usually a billion organisms per dose], relatively acid and bile tolerant to enable them to pass through the upper digestive system and still remain viable. A supplement that incorporates a combination of different species and strains may provide significant benefit, as different species of bacteria can supply nutrients to each other.
The best time to take your probiotic supplement is before food when there is little acid in the stomach, to ensure the bacteria reach the intestines in a viable form. Always store probiotics refrigerated as the bacteria are sensitive to heat; this will then ensure the most benefit.
Prebiotics
Prebiotic supplementation may also be considered and some supplements may incorporate a combination of probiotics and prebiotics. While probiotics provide bacteria to the gut, prebiotics provide a food source for the growth of bacteria already in the gut. Prebiotics may therefore potentiate the beneficial actions of the bacteria in the gut. Prebiotics are generally found in supplements as fructo-oligosaccharides (FOS).
