Probiotics comprise a large number of different strains of bacteria and other microorganisms, such as yeasts. When taken in adequate amounts, these live microorganisms can have measureable biological effects in the body and may confer health benefits. Probiotics have been consumed for thousands of years, and are now widely available for consumers in various forms, including capsules and dairy products such as live yogurt and yogurt drinks.
Strains from the bacterial genus Lactobacillus and Bifidobacterium are the probiotics most often present in products and experts in the field suggest that many well studied Lactobacillus andBifidobacterium species can be expected to have ‘generic’ or ‘core’ effects on gut physiology and health by creating a more favourable environment in the gut, through mechanisms shared by most probiotics. Furthermore, dietary guidelines in Estonia, Italy, Germany, Poland and Spain specifically recommend the addition of probiotics to the diet. However, the use of the word probiotic to describe products for sale in the EU has been banned, as the term is classed as a ‘generic descriptor’ which could imply an effect on health and no specific health claims have been permitted by the European Food Safety Authority in relation to any probiotics.
The results of scientific studies looking into the health effects of probiotics periodically hit the headlines, with suggested benefits including reducing hay fever symptoms and preventing antibiotic-associated gastrointestinal upset. Much of the research into probiotics focusses on specific health conditions, particularly those relating to the gut, such as irritable bowel syndrome and ulcerative colitis but emerging research suggests bioactivity reaching systems beyond the gut, such as modulating blood pressure, cholesterol, blood glucose and even cognitive function. Some research points specifically towards potential health effects in healthy individuals, including reducing the duration of a cold and improving very mild symptoms (such as abdominal pain and bloating) in individuals without a diagnosed gastrointestinal condition. These health effects are explored in more detail in an article in Nutrition Bulletin.
Probiotics is a complex area and when considering the results of research in this field it is important to take a number of factors into account:
Probiotics encompass a wide range of bacterial strains
Describing the effects of probiotics in general can be misleading because health effects may be specific to a single strain of bacteria, therefore grouping together the results of studies which have used different strains (or different combinations of strains) is likely to be unhelpful in determining health effects and could paint a distorted picture of the evidence. It is important to remember that each single strain has to be tested for each single health outcome before firm conclusions can be drawn. In addition, responses to probiotics can vary between individuals due to physiological differences, such as the baseline composition of the gut microbiota, therefore the number of subjects in each study needs to be sufficiently large to account for this.
Probiotics must be taken regularly and survive their passage through the gastro-intestinal tract.
To be effective and have an impact on health, probiotics must be able to survive the harsh conditions (particularly the acid in the stomach) during their passage through the intestinal tract. Survival rates tend to vary between different strains. Probiotics which do manage to recover and grow in the intestine can then influence the composition and activity of the gut microflora but in order to integrate into the gut microbiota (though transiently), probiotic strains need to be taken frequently, as they generally only persist in the gut for a short time.
The vehicle by which probiotics are delivered, and dose, are also important
It is also important to investigate whether probiotics are able to deliver health benefits in the vehicle through which they are delivered (e.g. capsules, dairy products) and the dose is sufficient to allow the probiotic to exert a health effect. Regulators in Canada and Italy have suggested that ingesting 109 viable colony forming units of a specific strain per day is required.
Derrien, M. and J. E. T. van Hylckama Vlieg (2015). “Fate, activity, and impact of ingested bacteria within the human gut microbiota.” Trends in Microbiology 23(6): 354-366.
Hill, C., F. Guarner, et al. (2014). “Expert consensus document: The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic.” Nat Rev Gastroenterol Hepatol 11(8): 506-514.
Lockyer, S. (2017). “Are probiotics useful for the average consumer?” Nutrition Bulletin 42(1): 42-48.
Smug, L., S. Salminen, et al. (2014). “Yoghurt and probiotic bacteria in dietary guidelines of the member states of the European Union.” Beneficial microbes 5(1): 61-66.
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