Of all the functional foods that claim to enhance health and performance, probiotics are perhaps the most popular. Around the globe over £20 billion is spent on them annually. But how effective are they for otherwise healthy people and are they useful for sporting performance?

What are Probiotics?

Probiotics can be defined as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.” As Outdoor Fitness has previously reported, in recent years, there’s been an explosion of research into the immunestimulatory properties of probiotics and some of these results have been encouraging. I’ve summarised some of this research below:

  •  A study that looked at the effects of probiotic supplementation on the duration, incidence and severity of infections in 30 elite rugby union players, and which found that probiotic use reduced the incidence, severity and duration of upper respiratory tract infections (URTIs) and tummy upsets(1).
  • A study on lactobacillus fermentum supplementation and gastrointestinal and respiratory-tract illness symptoms in 99 competitive cyclists(2). It found that probiotic use produced a marked reduction in tummy upsets during high-intensity training phases and a reduction in the duration and severity of URTI symptoms.
  • A study on runners who took lactobacillus fermentum, which found it significantly reduced the incidence and severity of URTI episodes(3).
  • A study of 84 athletes who took the probiotic supplement lactobacillus casei shirota. It found that the probiotic reduced the incidence of URTIs lasting over a week by around a third(4).

At this point, you’re probably thinking “Great – time to stock up the fridge with probiotic drinks!”

However, before you do, some caution is required. While these studies make for encouraging reading, there’s still considerable doubt about probiotic use. This is partly because in these studies, numerous strains of probiotic bacteria have been used, some of which may be far less effective than others.


There’s also the issue of how fresh or “viable” a probiotic supplement is and how resistant it is to degradation by naturally produced acid in the stomach. A recent review study (a study that pools together all the data from previous studies) into the benefits of probiotics was carried out last year by Chinese researchers(5). It concluded that probiotics did seem to reduce the number of participants experiencing episodes of an acute URTI, the mean duration of an episode of acute URTI, antibiotic use and cold-related school absence, and that probiotic use could be more beneficial than nothing.

However it also concluded that because of all the confounding variables, the quality of the evidence from these studies was low or very low, which therefore makes it very difficult to determine just how effective probiotic supplementation really is.

Viable alternative?

As if to underline this point, around the same time, a group of scientists at University College London was carrying out research into the viability of solid and liquid probiotic formulations(6).


The researchers looked at a probiotic called lactobacillis bacteria, which is found in a number of popular products on supermarket shelves. To be effective and therapeutic, probiotics have to be able to deliver a sufficient amount of the friendly bacteria they contain to the small intestine. Simply swallowing enough active bacteria is no guarantee, especially when faced with the very acidic conditions of the stomach, which the bacteria need to pass through before they can enter the small intestine.

So this study was designed to mimic the challenges faced during oral delivery.

These were:

  • Did the product provide the stated number of viable bacteria as per the labels claimed?
  • Could the bacteria survive exposure to stomach acid?
  • Could the bacteria thrive upon arrival in the gut?

The researchers compared eight commercially available products. The good news was that the liquid products (such as yoghurts and probiotic drinks) all contained viable bacteria equal to or more than the claimed amounts on the labels.

This was in contrast to solid probiotics (capsules and so on), which all contained fewer viable bacteria than the labels claimed. However, regardless of whether they supplied in liquid or solid form, all the products lost viable bacteria when exposed to the acidic gastric fluid.

Despite this, three of the products (Actimel, VSL3 and Symprove) maintained viable bacterial numbers for up 90 minutes after exposure to stomach acid, suggesting these products might be able to deliver useful amounts of bacteria to the small intestine of the gut, which is where they are able to deliver any potential benefits. An important implication of these findings is that any probiotic should be taken on an empty stomach and at least 15 minutes before food. This is because in these conditions, gastric emptying time will be faster, meaning less exposure of the bacteria to destructive stomach acid.

Conclusion and practical advice

Given the evidence, what can we conclude about the use of probiotics? Well, on balance, it seems that they might be able to deliver some health benefits to sportsmen and women in hard training – mainly in terms of supporting immunity.

However, due to the wide range of bacteria used in these different studies, and the problems in getting enough of the right bacteria through the stomach and into the gut, it’s by no means guaranteed that you’ll see tangible benefits if you take probiotics.

If you do decide to give them a try, the evidence suggests that liquid forms are likely to be more effective than tablet/capsule forms. It’s also vital that you take them on an empty tummy and at least 15 minutes before foods. A good time is soon after rising in the morning and before breakfast.

References 1. J Sci Med Sport. 2013 Aug 30. pii: S1440-2440(13)00190-4 2. Nutr J. 2011 Apr 11;10:30 3. Br J Sports Med. 2010 Mar;44(4):222-6 4. Int J Sport Nutr Exerc Metab. 2011 Feb;21(1):55-64 5. Cochrane Database Syst Rev. 2015 Feb 3;2:CD006895 6. Beneficial Microbes 2015, Vol. 6, No. 1, pp. 141-151