Probiotics have become an important topic of health conversations in recent years as scientists and the public became more aware of the importance of a healthy digestive system. 

However, probiotics are by no means a one-size-fits-all solution and the field is a relatively complex, fluid one.

What, exactly, are probiotics?

Probiotics are microorganisms (almost always bacteria) that have beneficial effects on the body and its functioning. These microorganisms are the same or similar to those already naturally occurring in the human body. Probiotic supplements are therefore commonly taken to correct a deficiency of specific bacteria.

Probiotics, both those that occur naturally in the body and those obtained from food and/or supplements, are largely concentrated in the gastrointestinal tract where they form part of your intestinal flora. Healthy intestinal flora is an essential part of digestion, and deficiencies here can have a number of negative health consequences.

The intestinal flora is made up of a vast range of different microorganisms, with most studies estimating that there are at least 500 different species of bacteria in the average gut. However, approximately 99% of the total mass is made up from just 30 or 40 main strains. It seems to be particularly important to maintain sufficient levels of these strains.

Interestingly, the actual make-up of the intestinal flora can vary widely from one individual to the next, but it’s unusual for a person’s intestinal flora to substantially change during the course of their adult life.

Some of the most commonly occurring strains are those in the Bacteroides family, which make up approximately 30% of all the bacteria in the gut.

Other important strains include:

    • Clostridium

    • Fusobacterium

    • Ruminococcus

    • Bifidobacterium, especially Bifidobacterium lactis

    • Peptostreptococcus

    • Lactobacillus

Why are probiotics beneficial?

Probiotics perform a wide range of functions important for maintaining good health, particularly related to digestion. Probiotic supplements can be taken preventatively, but are more often used to treat gastrointestinal problems that arise sporadically.

Constipation is one of the conditions most commonly treated with probiotics, either alone or in conjunction with other medication, such as a laxative or a prokinetic. Probiotics are specifically helpful in situations where constipation is caused by the improper or incomplete digestion of food. Such constipation is usually the result of imbalances in intestinal flora, and a probiotic supplement can help restore the imbalance. In this way, it allows you to regain the ability to properly digest food.

At the other end of the scale, probiotics are also often indicated in the treatment of diarrhoea. Here they perform a dual role: firstly, a probiotic supplement can ensure that the gut flora remains healthy and well-balanced. This could speed up the return to normal defecation. Secondly, serious diarrhoea can cause the gut flora to become depleted, which can slow recovery. In some cases, symptoms may even worsen. Supplementation of Lactobacillus acidophilus and Lactobacillus plantarum seems to be particularly useful. Traditionally, the plantarum strain was administered alone, but modern best practice includes both Lactobacillus plantarum and Lactobacillus acidophilus for increased efficacy.

Both constipation and diarrhoea can also be caused by other medications taken for unrelated conditions, particularly strong anti-inflammatories and antibiotics (more on this later). In such cases, a probiotic supplement is often prescribed along with the medication to minimise the gastrointestinal side effects. These probiotics are usually taken for some time after the course of the primary medication has been completed to properly restore the balance of the gut flora.

Probiotics have also been shown to be effective in helping people with lactose intolerance minimise their symptoms. Bloating, cramping, flatulence and diarrhoea can cause substantial discomfort to those with lactose intolerance, forcing them to adopt restricted diets. There is currently no cure for lactose intolerance, but certain treatments are available to improve individuals’ tolerance of lactose. Probiotics are increasingly recommended as a method to help people with lactose intolerance better digest lactose. Lactobacillus acidophilus in particular has been shown to be greatly effective in boosting levels of the lactose-digesting enzyme, lactase, in the gastrointestinal tract.

Preliminary research shows that probiotics may also be beneficial in the management of inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis.

Why antibiotics disrupt the balance of intestinal bacteria
Antibiotics are very commonly prescribed – either as a primary intervention to treat bacterial infection or to prevent infection (following surgery, for instance). While antibiotics are highly effective, they can also have a number of unpleasant side effects.

The most common side effects are diarrhoea and nausea. This is simply because, along with killing harmful bacteria, antibiotics also destroy many of the important, beneficial microorganisms that make up the intestinal flora. In its place Candida albicans, a fungus that naturally occurs in humans, quickly flourishes. An overgrowth of Candida albicans can cause a number of yeast infections, most notably thrush. Taking a probiotic can help to regenerate the beneficial bacteria in the gut, preventing the proliferation of Candida albicans and either minimising the severity of, or totally negating, these unpleasant side effects.

A 2003 study in the Journal of Antimicrobial Chemotherapy observed the effects of supplementary probiotics in people taking the antibiotic clindamycin. When compared to placebos, Lactobacillus acidophilus, Bifidobacterium lactis and Lactobacillus F19 were shown to be effective in preventing antibiotic-associated imbalances. In total, the number of helpful microorganisms remained the same in people taking the probiotic, whereas the placebo group saw a notable decrease. This finding is particularly important for elderly and immune-compromised people, for whom these side effects can be severe.

Research furthermore indicates that probiotic supplements may be useful for people who are being treated for Helicobacter pylori infection, the cause of most stomach ulcers.

Why are probiotics beneficial in terms of immunity?
Certain types of gut bacteria may also be involved in functions related to the body’s immune system. Researchers from Harvard Medical School have found evidence that certain bacteria aid in T-cell production, and correcting mineral and nutrient deficiencies.

In addition, the gut presents a substantial opportunity for infection, given its exposure to harmful microorganisms from food. Healthy intestinal flora works to produce a barrier between ingested food and the internal tissues of the body. Were this boundary to lie unwatched, the potential for infection is substantial. A deficiency in certain beneficial bacteria could weaken this defence mechanism and, on occasion, allow for infection. Food poisoning in particular becomes a much greater threat to people with poorly maintained gut flora.

A probiotic supplement can help to maintain the levels of helpful bacteria necessary to ensure that this barrier remains effective, and thus minimise the chance of infection. A study in the American Journal of Clinical Nutrition reported that probiotics were positively associated with a normalisation of the intestine’s permeability. Probiotics also helped to alleviate inflammatory responses within the intestine. A study of elderly patients showed that three weeks of Bifidobacterium probiotic supplementation increased the activity of tumour-killing cells by between 62 and 101%, depending on the strain of bacteria used.

Which probiotic is right for me?

To recap, these strains of bacteria have been shown to be beneficial in these particular instances:

    • To prevent or treat diarrhoea: Lactobacillus acidophilus, Lactobacillus plantarum

    • To help manage lactose intolerance: Lactobacillus acidophilus

    • To counter the effects of antibiotics: Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus F19

    • To boost immunity: Howaru Bifido

Choose a probiotic supplement that best suits your needs and your particular diagnosis or health condition at any given time. Simply look for the appropriate strains on the product label, or ask your doctor or pharmacist for assistance.

Also keep in mind that one of the most important factors to look for in a probiotic supplement is the ability to negotiate the harsh conditions of the stomach. Due to the amount of hydrochloric acid secreted by the stomach, the pH can reach as low as 1. For a probiotic to be effective, it needs to be able to survive in this highly acidic environment.

Give these healthy bacteria the best chance of getting where they need to go by making sure you eat before taking the supplement. Having food in the stomach neutralises the pH to create a more habitable environment. Also check that the probiotic comes with some kind of prebiotic, such as inulin. A prebiotic provides “food” for the bacteria in the probiotic supplement. This helps to maximise the amount of beneficial bacteria that survive the journey to the intestine.

Lastly, keep in mind that probiotics can’t replace conventional treatment methods. If diarrhoea persists, or if you think you may be lactose intolerant or have another serious gastrointestinal problem, it’s important to consult a doctor.

- Sullivan, A., Barkholt., & Nord C.E. (2003) Lactobacillus acidophilus, Bifidobacterium lactis and Lactobacillus F19 prevent antibiotic-associated ecological disturbances of Bacteroides fragilis in the intestine. Journal of Antimicrobial Chemotherapy. 52 (2).
- Isolauri, E., Sutas,Y., Kankaanpaa, P., Arvilommi, H., & Salminen, S. (2009) Probiotics: effects on immunity. The American Journal of Clinical Nutrition.
- Gill, H.S., Rutherfurd, K.J., & Cross, M.L. (2001) Dietary probiotic supplementation enhances natural killer cell activity in the elderly: an investigation of age-related immunological changes. Journal of Clinical Immunology. (21).
- Dupont, H.L. (2014) Review article: evidence for the role of gut microbiota in irritable bowel syndrome and its potential influence on therapeutic targets. Alimentary Pharmacology & Therapeutics.

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