We all want to feel good – ideally without having to do anything for it. This provides great opportunities for manufacturers of health products. Homeopaths do particularly well in this field. But despite these charlatans can we really condemn all the products that claim to make us feel better? Well, of course we can’t, but we need scientific experiments, especially clinical trials, to find out what’s quackery and what’s not.

Since the turn of the millennium we've been flooded with more than 2000 probiotic products. Claims that fermented milk products benefit health were mostly anecdotal, and more or less date back to the Nobel laureat Ilya Mechnikov. In the proceeding 100 years, more than 700 clinical trial were conducted and in excess of 1000 research articles dealing with probiotics have been published.

Advances in metagenomics continue to raise our awareness of our intimate coexistence with bacteria on and in our body. Most of these bacteria are commensal that means they neither harm nor help. Although by just being there they fill the niche that could otherwise be occupied by pathogens. And for this we should be grateful. Antibiotic treatments disturb this balance as the drug kills bacteria without differentiating between friend and foe, allowing opportunistic bacteria to fill the gap. An opportunist that recently caught our attention is Clostridium difficile. This organism is particularly successful in hospitals as the intestines of people, weakend by illness and antibiotics, are easily colonized. Patients that acquire a C. difficile infection develop antibiotic associated diarrhea. Clever use of probiotics in these instances can reduce the risk associated with these infections and thus save lives.
With some bacteria however we evolved a much tighter, symbiotic relationship. While we provide food and shelter, Lactobacillus gasseri for example primes our immune system and increases the number of T-lymphocytes, which in turn shortens the time we suffer from common cold, Streptococcus salivarius fights off bad breath, Lactobacillus rhamnosus and Lactobacillus fermentum improve vaginal health and Lactobacillus paracasei keeps our skin healthy.
A decrease of intestinal symbionts can trigger allergies or chronic inflamations. Crohn’s disease is probably the most prominent example. Supplementing food with well-defined probiotics has the potential to considerably ease this condition.

We have come a long way since manufacturing of some of the first probiotic products involved heat inactivation. Keeping bacteria alive certainly improves the activity of probiotics, but other factors deserve attention too. Bacterial cultures follow a characteristic growth curve in ideal conditions. This curve consists of a lag phase at the beginning in which bacteria adjust to the new conditions and grow very slowly if at all. The logarithmic phase follows, now the organisms are at their best and double in given intervals until the culture reaches a maximum cell density determined by the amount of nutrients. For some time the number of cells can be maintained before the bacteria die or enter some sort of hibernation state. Each phase comes with a certain set of genes activated and it takes time to switch from one state to another. Time the bacteria don’t necessarily have when they enter a highly competitive environment such as the gut. Usually the log-phase status is best suited for conquering new grounds. This brings us to the problem that arises in mass production of probiotics. Once we bottle a bacterial culture i.e. the yoghurt and store it in a fridge the situation for the bacteria changes dramatically and we end up ingesting a bacterial culture that is less potent than it could be. Some producers aim to circumvent the problem by isolating and drying the bacteria so that they can be served in pill or powder form. This procedure comes with its own set of problems. But if we don’t want to produce yoghurts ourselves, which is by the way not that difficult and still involves chilling and most likely storage of the sample, we have to cope with sub-optimal probiotics. Thus any clinical trial involving probiotics needs to account for this by using final products rather than bacteria straight from a growing culture. Luckily this appears to be the case.

So, should we eat our daily probiotic yoghurt? Reading the label we realize that it contains only a very limited variety of bacterial organism. The one I’m drinking now contains L. bulgaricus, S. thermophilus and L. casei. What shall I expect from this? Probably not so much from S. thermophilus, in healthy individuals they don’t make it past the stomach, but L. bulgaricus and L. casei should be of more use, they convert lactose into lactic acid. Something that should make lactose intolerant people happier and they also stimulate the immune system and thus help us to ward of infections. For me that’s good enough.

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