Friday, October 28, 2011

Probiotics affect body without populating intestines

Lots of claims have been made about probiotics; dairy products that contain a set of bacteria that are supposed to improve our gut flora. It is claimed, mostly by the companies that produce them, that they improve our digestion and metabolism, but none of these effects have ever been properly shown in a scientific study. However, a recent study shows that there might be beneficial effect of probiotic products. While the ingested bacteria do not seem to stick in the gut, where a lot of other human populating bacteria are, the metabolism of people who consume yoghurt with micro-organisms may be altered. While the implications of this study are yet to be unraveled, it could be that probiotics have a beneficial effect after all, even though it might be small.

For their study, the researchers fed fermented milk products with five strains of bacteria to mice and humans. After that, genetic analysis revealed the ingested bacteria were unable to stay in the gut, passing right through into the faeces. In the process, they also seemed unable to affect the local population: bacteria native to the gut remained unchanged after a regime of probiotics ingestion. For their measurements, the scientists compared identical twins, to exclude any genetic differences that have an additional effect, and to make sure that the people who are compared with each other have the same gut flora.

When the scientists looked at the expression of known genes involved with metabolism, they found that mice upregulated genes that are involved with breaking down sugars that are found in fruits and vegetables. This hints at an increased metabolic rate for these sugars, which possibly has a beneficial effect. They found a comparable metabolic pattern when looking at the genes of human participants. The changes in gene activity consequently dissapeared after the periodical ingestion of probiotics ended. This could mean we are better able to digest plant material if we consume probiotics, but a gene analysis only does not tell you anything about the functional level yet.

The study was funded by Danone, a company that produces probiotic dairy products. Naturally, they want scientific results that a beneficial effect of their products. While the researchers that were paid by the company did find some metabolic changes, the implications of this study still need to be investigated. Even with an increased activity of genes involved with the breakdown of certain sugars, it does not lead up to a conclusion that probiotics have health benefits.

Effects of probiotics were also studied in mice, because it is hard to find people that have the same type of gut flora, and corresponding metabolism. A specific mouse model has been made that contains a set of 15 bacterial strains which are found in humans. This way, the mice mimic the human gut flora, while still maintaining similarity between individuals. It is important to have a model that are comparable in gut flora, because else it is hard to make comparisons, as the differences between individuals obscure the test results.

Future research in this so-called gnotobiotic mouse model will need to tell us how we need to mix different bacterial strains and their quantities to achieve a beneficial health effect. Even with this study, there is no real prove that probiotics improve your health.

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