It is hard to shop these days without noticing the phrase “probiotic bacteria” jumping out from food labels. Turn on the TV and many an advert break features bright-looking yoghurts and yoghurt-style drinks full of unpronounceable microbes with equally bright young things cavorting around giving us the impression that whatever probiotics do, it must be something good.

Probiotics are, in fact, naturally present in our guts and have long been recognised to be of benefit to our wellbeing. This is because they help to maintain a balance between themselves and the billions of harmful bacteria that also live there.

The theory goes that because of our exposure to stress, pollution and drugs such as antibiotics, this delicate balance is disrupted, and has been linked to triggering everything from bloating, lowered immunity and asthma, to allergies, raised cholesterol, increased susceptibility to stomach ulcers, food poisoning and even cancer of the colon.

Research is starting to reveal some fascinating effects of a regular and continued daily dose of certain specific types of “good” bacteria. Because probiotics are naturally present in only very few foods, the number of probiotically fortified products in recent years has mushroomed. But do you go for the Müller Vitality drink which, its makers say, helps you to maintain a healthy digestive system? Or Danone Actimel, which claims to support the body's defences by topping up levels of good bacteria in our guts? Or what about those quirky little milk-shots, Yakult, which, if the blurb on the side of the bottle is to be believed, is “a healthy start to every day”?

Probiotics such as Lactobacillus gasseri, Bifidobacterium bifidum and Bifdobacterium longum in the supplement Multibionta are proving to be especially capable of improving the immune system. They appear to have a role in preventing colds while others are showing themselves to be especially effective at reducing symptoms of bloating associated with irritable bowel syndrome (IBS).

Yakult, which hails from Japan, is made from skimmed milk with added Lactobacillus casei Shirota. It has undergone extensive clinical trials, and the results suggest that a daily shot may play a role in everything from improving IBS and modulating immunity to reducing the presence of Helicobacter pylori, the bacteria that causes stomach ulcers. It also seems to help with constipation and to lower the pH of the bowel, which in turn defends against the growth of putrefying bacteria and toxins that could otherwise trigger cancer.

Activia, a creamy yoghurt made by Danone, contains a culture of probiotics called Bifidus ActiRegularis. Research reveals that this particular good bacteria helps to improve slower digestive transit. According to Danone, a slower transit may make you occasionally feel bloated and Activia is the only yoghurt in the UK scientifically proven to help to improve slower digestive transit. In other words, it is being hailed as the “anti-bloating” probiotic product.

Always go for a well-known brand that specifically names its probiotic content. This is because all yoghurts contain “live” bacteria (these are added to milk to produce the fermentation that causes the milk to set into a yoghurt), but not all live bacteria have probiotic properties.

A dose of between 5 billion and 10 billion live probiotic bacteria a day is a sufficient amount to maintain healthy intestinal flora. Although it is not possible to “overdose” on probiotics, more than 20 billion a day is not thought to have added benefit.For maximum effectiveness you must consume probiotics every day - especially if you have been prescribed antibiotics. Taking them before a holiday is also a good idea as it may reduce the risk of picking up bugs from fellow travellers or from dodgy food or water.

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