Prebiotics and Probiotics – The Keys to Balancing your Gut Flora

Charlene Grosse, IBS Dietitian Perth

Our gut is the largest immune organ in the body, with more than 70% of the immune cells residing there. The healthy human GI tract contains around 10 times as many bacteria as there are cells in the human body. Most of these bacteria (named the microbiota) either provide a functional benefit or are doing no harm. The microbiota is extremely varied with up to 1000 different bacterial species, together containing 100 times as many genes as the human genome. This genetic pool is referred to as the microbiome. Relatively little is known about the human microbiota or the microbiome, although research is looking at defining and establishing how the bacteria and their genes interact with the human host.

The normal gut microflora activity is complex and since little is known about it the mechanisms of action are poorly understood. Current proposed influences are listed in Table 1.

Table 1. Gut Microbiota

Major Phyla (groups) in the human gut Major functions of gut microbiota Major contributing factors shaping gut microbiota
Firmicutes Digestion Diet
Bacterioidetes Regulation of immunity Genetics
Actinobacteria Maintenance of bacterial balance in the gut Sanitation/environmental cleanliness
Preoteobacteria Nutrient and energy regulation Environmental exposures (e.g pollution)

When assessing contributing factors, diet is critical in managing gut microbiota. Studies have shown a change in gut bacteria can occur within 24 hours following a dietary change.

The gut microbiota can be influenced by the following:

  • Children inherit their microbiome from their mother at the time of delivery and during breast-feeding.
  • When the mother’s diet results in an imbalanced microbiome, this is passed onto the child who will have less than ideal bacteria for proper immune functioning.
  • High fat intakes are thought to increase inflammation and affect the immune systems interaction with the guts bacterial environment.
  • High sugar diets can cause harmful bacteria to dominate over beneficial bacteria.

An altered microbiome is thought to predispose individuals to many chronic diseases, such as obesity, diabetes and cardiovascular disease.

Its all about balance

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When the balance of beneficial and harmful bacteria is altered it can lead to problems such as diarrhoea, bloating, wind, constipation, discomfort and generally feeling below par. This balance can be altered if you take antibiotics and after a bout of food poisoning or ‘travellers’ diarrhoea. It can also be affected by diets that contain little fruit and vegetables or that are high in fat and/or alcohol.

Beneficial bacteria, comprised mainly of Lactobacillus and Bifidobacteria, can improve your digestion, fight off harmful bacteria and increase nutrient availability which helps to keep your bowels functioning. A healthy digestive system has a good balance of both good and bad bacteria. Ensuring a balance between good and bad bacteria is important for overall health as harmful bacteria can produce toxins and cause infection and disease.

In most people the correct balance of good bacteria is maintained in the digestive system by eating a variety of healthy foods. This includes a diet rich in fruit, vegetables, wholegrain breads & cereals, yoghurts containing live active bacteria and dried beans and lentils.

What are probiotics?

Probiotics are defined as ‘live organisms which when administered in adequate amounts confer a health benefit on the host’ (FAO/WHO 2001). This means that to be a probiotic the microorganism:

  • Must be proven to reach the intestines alive
  • Be safe for human consumption
  • Present in sufficient quantities
  • Has demonstrated shelf stability
  • Has been shown to have a positive health effect in controlled human studies

Recognition of probiotic effects dates back to the 19th century when the French scientist Louis Pasteur (1822 –1895) postulated the importance of microorganisms in human life; this was further reinforced by work done by 1908 Nobel Prize-winner Elie Metchnikoff. It is not completely understood how probiotics work however some basic principles include limiting bad bacteria, improving the barrier function of the gut and modulating the immune system.

Benefits of probiotics

There is a lot of interest in the use of probiotics in foods and as a supplement worldwide with the growing evidence of their health benefits to:

  • Boost the immune system
  • Increase resistance to infection
  • Help in the prevention and treatment of diarrhoea resulting from bacterial infection
  • Help to prevent diarrhoea resulting from antibiotic therapy
  • Improve bowel movements
  • May help improve mild inflammation of the bowel

What are Prebiotics?

A prebiotic is a food substance that specifically promotes the growth of good bacteria in the bowel. These foods need to resist digestion in the small intestine so that they arrive relatively unchanged in the large bowel to interact with the good bacteria. Good sources include onions, garlic, banana, leeks, asparagus, Jerusalem artichokes and wheat bran. Including prebiotics in your diet can help maintain digestive balance by providing fuel for the beneficial bacteria in the body.

Prebiotics vs Probiotics

While prebiotics and probiotics sound very similar there is actually a difference between them. In a nutshell, probiotics are live strains of bacteria – including bifidobacteria and lactobacilli – that live in our digestive systems and prebiotics are nourishment that this bacteria needs to stimulate growth. Probiotics and prebiotics work together to maintain a healthy digestive system. Because probiotic bacteria are often eliminated in the gut, prebiotic foods are needed to ensure their survival. So prebiotics are important for stimulating the growth of the probiotics (good bacteria).

Can you take prebiotics and probiotics together?

Taking a probiotic with a prebiotic has been shown to promote its survival and colonisation in the bowel. The combination of a probiotic with a prebiotic is referred to as a symbiotic. Both work together in a synergistic way more efficiently promoting the probiotics’ benefits.

Prebiotic and Probiotics in Foods

With the new scientific paradigms for probiotics and prebiotics it is important to look at food and beverage sources of probiotic microorganisms and how they fit into gut health.

Live cultures versus probiotics

The term live cultures and probiotics are not the same. Live cultures are specific microorganisms added to foods to create the fermentation process.

The ingestion of live microorganisms in the food supply is not a new concept. Fermented milks have been produced and consumed all over the world for many thousands of years. Fermented milks are prepared from pasteurised milk and milk products through the action of ‘live cultures’. This results in a reduction in pH and coagulation of the product. Yoghurt and kefir are two examples of fermented milk products.

Fermented foods

Fermentation is a metabolic process that converts carbohydrates to acids, gases or alcohol using live microorganisms. Lactic acid fermentation is the utilisation of various sugars by bacteria to produce lactic acid. Lactic acid provides a sour taste and flavour to foods, promotes preservation and has health giving properties. Fermented foods include products such as sour pickles, kimchi, kombucha, sauerkraut, yoghurt, miso soup and fermented milk drinks. Not all bacteria present in fermented milk products or yogurt have a probiotic effect.

Further research is required to understand how these foods affect the gut microbiome.

Table 2. Prebiotic and Probiotic in Foods

Prebiotic rich foods Probiotic rich foods
Asparagus (raw) Yoghurt
Chicory root (raw) Kefir
Jerusalem artichoke (raw) Sauerkraut
Dandelion greens (raw) Miso soup
Garlic (raw) Sour pickles
Onions (raw and cooked) Tempeh
Leeks (raw) Kimchi
Banana (raw) Kombucha tea
Wheat bran (raw)
Whole wheat flour

Probiotic Supplements

It is important to understand that the effects of probiotic bacteria and yeasts are strain specific and therefore specific to a disease or diagnosis. Different strains will offer varying benefits, hence, there is not one universal probiotic. Different strains of the same species will have different probiotic properties and can have a different mechanism of action in the body. When looking at probiotics finding one for example with lactobacillus is not enough. You need to discuss with your health professional correct genus, species and strain for your health condition and how this translates to a supermarket supplement or food product. Often this can be difficult, as the strain studied does not usually exist as a purchased probiotic supplement.

Dosage of Probiotics

Dosage is still an important area that needs to be addressed in future research. The dosage of a probiotic strain provides an indication of the number of live microorganisms present in a food or supplement. On average, dosages required to achieve beneficial effects are commonly reported to be above 100 million (Colony Forming Units) per day. It is not possible however, to provide one dose for all probiotic foods and supplements. For the best results it is recommended to have the dose and strain that has shown a positive result in research. A larger dose does not mean an enhanced effect and multiple strains does not necessarily equate to a more effective product. More research is required to determine optimal dosage and strains.

Taking a probiotic does not lead to long-term colonisation and survival in the digestive tract. Probiotics must be taken regularly otherwise they will be diluted out of the colon within one to two weeks of ingestion, unless there is continuous intake.

Choosing the Right Probiotic

The strain of the probiotic determines how the probiotic will function in the human body – therefore you need to know:

  • Which microorganism does the product contain
  • How many live micro organisms are there per serve

  • Does the product list health benefits? If so are there published studies on this specific strain in the product?

  • Is it the original product you are consuming or a replica of one that has been well researched

  • Is the mode of delivery the same as the food you are investigating (food, capsule, powder), what were the dosages provided to the study group, is it the same as the food product is recommending>, is the study group population the same?

A good probiotic will need to;

  • Contain bacteria that can reach the small or large intestine without being damaged

  • Contain large numbers of bacteria

  • Be taken on a daily basis

Safety of Probiotics

The majority of scientific studies completed to date have described a good tolerance to probiotic preparations and the absence of significant side effects. Most commercially available probiotics are considered safe; however, the safety of one strain cannot be extrapolated to another.

There are concerns with the use of probiotics in some patient groups specifically those who are critically ill or severely immunocompromised. Caution should also be taken for anyone with an allergy to cow’s milk. If you are a healthy individual probiotics are generally considered safe for the Lactobacillus and Bifidobacterium species used in the food industry and clinical trials in the general adult and paediatric populations.

Who needs probiotics and prebiotics?

Research shows that probiotics are a promising therapy for a wide range of health problems including IBS. Probiotics can additionally help in reducing health risks of some cancers. These health benefits are strain and dose specific – you need to know the exact strain not just the species and the dose must be the same as that used in the clinical trials. Translating the strain into a supermarket brand is difficult as it is often not available as a supplement.

A trial of probiotics may be worth undertaking if you have recently had an upset stomach or have started a course of antibiotics that has triggered your IBS. In general they are safe to take for most people of all ages. However, if your immune system is not working properly or if you are taking drugs that affect your immune system, including some cancer treatments, you should avoid probiotics.

Clinical guidelines recommend that individuals choosing to try probiotics should select one product at a time and monitor the effects. They should try it for a minimum of 4 weeks at the dose recommended by the manufacturer.

The Bottom Line

Both prebiotics and probiotics play an important role in our gut health by affecting the balance of the gut microflora. Eating plenty of fibre rich food supports the growth of beneficial bacteria in the digestive system. These foods include:

  • Fruit and vegetables

  • Dried beans and lentils

  • Wholegrain breads and cereals

  • Yoghurts containing live / active bacteria

Although benefits vary, depending on the type and amount of a pre- or probiotic consumed, experts agree that daily consumption of foods containing these functional components is beneficial. In addition, the effects of probiotics are strain-specific and must be demonstrated through appropriate clinical trials.

An Accredited Practising Dietitian specialising in gut health can help you plan a healthy diet that is rich in both prebiotics and probiotics. Furthermore they can help you translate the science of probiotics and prebiotics in dietetics practice to help you achieve a happy healthy gut.

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