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What Are the Benefits of Probiotics?

The idea that there are more than a trillion bacteria living in the human digestive system may make you shudder. But the vast majority of these little bugs – often described as ‘good’ bacteria or, if you’re a medical professional, gut microbiota – are considered crucial for health and wellbeing.

If you’re healthy, up to 90 percent of the bacteria in your digestive system may be beneficial, with the remaining 10 percent considered less than beneficial (or even potentially harmful). The problem is the ratio of ‘good’ to ‘bad’ bacteria can become upset as a result of a number of things, such as your diet, stress, illness and as a side effect of taking antibiotic treatments.

The good news for those who lead an active lifestyle is that exercise is thought to help increase your level of beneficial gut bacteria. One study, published in the journal Gut (i), suggests exercise, especially when combined with a protein-rich diet, may boost the amount and number of different types of gut bacteria.

Another way of maintaining a healthy balance of intestinal bacteria is to add probiotics to your diet. Commonly referred to as ‘friendly’ bacteria, probiotics are living microorganisms found in certain fermented foods as well as supplement products. They help maintain a healthy balance of intestinal bacteria, as they act as a barrier against potentially harmful bacteria that pass through your digestive system, making sure those harmful bacteria don’t take up residence in your gut.

Probiotics also come in many strains, and have names such as Lactobacillus acidophilus, which helps to prevent the growth of common disease-causing organisms such as E. coli and C. difficile.

Improved digestion and gut health

The health benefit most people associate with probiotics is, unsurprisingly, improved digestion and gut health. Around a third of the population in the UK is thought to be affected by problems such as irritable bowel syndrome (IBS), constipation and diarrhoea, with an estimated three million of us thought to be suffering from sluggish digestion. However clinical studies far too numerous to mention here suggest taking probiotics may be an effective way to protect against these and other digestive problems, including gastroenteritis and even stress-related gastrointestinal problems.

And if you take other nutritional supplements, by boosting your gut health probiotics may help your body absorb your supplements more effectively.

However better gut health isn’t the only thing probiotics may be useful for…

Immune health

Since the gut is thought to control around 60 percent of the immune system, what's good for the gut may also be good for the body's natural resistance to infection – a connection that many researchers have made during recent years if the number of studies investigating the role of probiotics in immune function is anything to go by.

Experts from the Australian Institute of Sport have concluded that probiotic supplements may protect long distance runners from respiratory illness by boosting the activity of important cells in the immune system called T cells (iii).


Stress is thought to play a role in many health problems and many believe it also affects athletic performance, especially when it has an effect on your digestion. Indeed, it is widely acknowledged these days that stress can trigger the symptoms of digestive problems such as IBS and diarrhoea. And if you’re already affected by such a problem, being under too much stress is highly likely to make your symptoms more severe.

Stress is also thought to affect the immune system, which has already been mentioned – is strongly connected with digestive health. But there’s evidence that probiotics may help. One study claims taking a probiotic supplement may reduce the some of the symptoms of stress-induced gastrointestinal symptoms, such as abdominal pain, nausea and vomiting (iv).

Weight control

Since probiotics affect the health of your digestive system, may they also help you to manage your weight? There may well be links between the two, since studies claim people who are of a normal weight have a different mix of gut bacteria than those who are overweight or obese.

One study, published in the journal Nature, points out that there are two groups of beneficial bacteria that are dominant in the human gut, namely bacteriodetes and firmicutes. But people who are obese have a lower level of bacteriodetes compared with those who are of normal weight (v).

Another study carried out by Japanese researchers found that certain probiotics – including those from the Lacbobacillus family – may prevent the digestive system from absorbing dietary fat (vii).

Various other health benefits have been credited to probiotics, including their impact on blood pressure, cholesterol, allergy symptoms, anxiety, depression, bone health and even dandruff. 

If you work out vigorously, there’s also evidence that taking certain strains of probiotics may help reduce post-exercise inflammation (ix). This could mean your muscles recover more quickly following a strenuous exercise bout.

How to take probiotics

Whether you eat foods that contain probiotics – such as ‘live’ yoghurt, kefir, sauerkraut, kimchi, miso, tempeh, kombucha, pickles and apple cider vinegar – or take a daily probiotic supplement, the key to getting the most out of them is to make sure you get a combination of different strains of bacteria, since this is thought to make it more difficult for unwanted bacteria to colonise the gut.

This may be easier to achieve if you take a good-quality probiotic supplement, since many are multi-strain formulations that deliver billions of bacteria per capsule. Indeed, since these quality probiotic supplements have billions of bacteria in each capsule, you may have to drink up to 50 or more probiotic dairy drinks to get the same benefit. However, kefir – a drink made from fermented milk – may be the exception, since some products have been found to contain enormous numbers (150 to 950 billion) of probiotic organisms per cup.

Probiotics are also thought to survive for just a few days to around three weeks in the human body after you stop taking them, which suggests if you want to continue reaping the benefits you should take them on an ongoing basis.


  1. , et al. Exercise and associated dietary extremes impact on gut microbial diversity. Gut. ;63(12):1913-20. (

  2. , et al. Effect of probiotic on innate inflammatory response and viral shedding in experimental rhinovirus infection – a randomised controlled trial. Beneficial Microbes: 8 (2), 207-215. (

  3. , et al. Probiotic supplementation for respiratory and gastrointestinal illness symptoms in healthy physically active individuals. Clinical Nutrition. Volume 33, Issue 4, Pages 581–587.(

  4. , , , . Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes. Br J Sports Med. ;44(4):222-6. (

  5. (

  6. , , ,. Microbial ecology: human gut microbes associated with obesity. Nature. ;444(7122):1022-3. (

  7. , et al. Lactobacillus gasseri SBT2055 suppresses fatty acid release through enlargement of fat emulsion size in vitro and promotes fecal fat excretion in healthy Japanese subjects. Lipids Health Dis. ;14:20. (

  8. , et al. Effect of Lactobacillus gasseri SBT2055 in fermented milk on abdominal adiposity in adults in a randomised controlled trial. Br J Nutr. ;110(9):1696-703.(

  9. , et al. Probiotic Streptococcus thermophilus FP4 and Bifidobacterium breve BR03 Supplementation Attenuates Performance and Range-of-Motion Decrements Following Muscle Damaging Exercise. Nutrients. ,8(10), 642. (

Our Author - Keri Filtness


Keri Filtness has worked in the Nutrition Industry for 19 years. She is regularly called upon for her professional comments on health and nutrition related news. Her opinions have been featured by BBC3, Prima, Vitality, The Mirror, Woman’s Own and Cycling Weekly, amongst others. She has also worked one to one with journalists, analysing their diets and health concerns and recommending changes and additions, where appropriate.

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