One of the biggest sellers on the supplement shelves are probiotics. You have probably heard about some of their benefits. Many people are aware that they can be useful after taking antibiotics. But their value for our health goes far beyond that.

By definition, probiotics are 'live microorganisms which when administered in adequate amounts confer a health benefit on the host' (WHO). Certain probiotics have been shown to prevent, relieve and speed up recovery from various types of diarrhoea, be it antibiotic-induced or traveller's diarrhoea. Probiotics produce vitamins K, biotin, B1, B2, B6 and B12. They also aid digestion and relieve malabsorption and constipation. They help to treat colitis, irritable bowel syndrome, Crohn's disease, food allergies and lactose intolerance. Not limited to effects on the digestive tract, they can improve immune function and prevent infections, help people with dermatitis or eczema, reduce the risk of kidney stones and certain cancers, lower cholesterol and blood pressure and have been found to be of great benefit to premature or acutely ill babies. There also seems to be a relationship between gut flora composition and body weight. Seem like a wonder drug to you?

Well, there are also some common misconceptions. Before we look at them, let's start with the basics. Each person has about 1.5 kilograms (!) of bacteria, yeasts and other microbes in their gut. To put it another way: you have around ten trillion cells in your body (that is a one with 13 zeros) – and about ten times as many microorganisms in your gut. Some of them are good, and these are the ones that you can take in a capsule or powder as a 'probiotic'. Some are bad, stealing your nutrients, potentially affecting your health or directly causing disease. And some are mostly neither here nor there but can go cranky on you under certain conditions. It is all a matter of the right balance, of who is getting to critical numbers. The most common thing to disrupt this balance is ...?

No, NOT antibiotic use, as a common myth suggests, but stress. Long term stress changes the environment in our guts in a way that doesn't much bother the bad and rather useless characters in our gut flora, but is not well tolerated by the good guys. Stressed, anyone? Ever seen your health go down during or after a stressful period? Got an infection as soon as you got a rest? Or a bout of thrush maybe? While there is a range of reasons why long-term stress isn't great for our health, your symptoms may have been a greeting from a couple of trillion 'friends' in your tummy.

Common myth number two: Antibiotics 'wipe out' your gut flora. Think about it: 1.5kg of microbes living there happily under normal circumstances. Have you ever lost that much weight from taking antibiotics? I'm sure some quack would have started to sell them as weight-loss drugs by now. Yes, antibiotics do affect gut flora. But it is again more a shift in the balance than a 'wipe out'. Humans could actually survive without any gut flora and all of us have sterile guts until birth. But once we pick up our first gut friends from our mother and the environment outside her belly, there is no way back. So for most people, a (hopefully well indicated) course of antibiotics will only make a short term dent in your bowel flora without noticeable health problems.

Yet to prevent any potential issues or if you already have digestive or immune problems – or stress –, it might still be a good idea to take probiotics during antibiotic treatment (as far apart as possible, i.e. if you take your anitibiotic in the morning, take your probiotic at night) and for about six to eight weeks after. Certainly, if you are getting diarrhoea from your antibiotics, probiotics are the way to go. In that case, you might want to see a naturopath to make sure you take the right stuff and that there isn't something else going on. A naturopath may also be able to help you pick a probiotic strain that is resistant to the specific antibiotic you take. It is important that you discuss any problems with your doctor but don't expect them to know as much about probiotics as a well trained naturopath.