By Dov Michaeli
Yesterday we discussed the deleterious effect that antibiotics have on the normal gut flora. Clostridium difficile can take advantage of the biological vacuum created by antibiotics and populate the gut –which leads to a serious complication called “psudomembranous colitis”. There is only one antibiotic that is still effective against this bug, and even it is losing its effectiveness through the emergence of resistant strains. So here is a question: why not seed the gut with beneficial bacteria, before C. difficile takes hold?
Some nutritionists claimed that bacteria provided by a probiotic diet can do just that. I have been quite skeptical; It looked suspiciously just another New Age fad. Consider the facts. The gut contains 100 trillion bacteria. So how could a few billion of added bacteria make any difference in the gut flora and in its metabolism?
In yesterday’s posting we described an experiment by Jeremy Nicholson of Imperial College in London, in which he showed that replacing the gut flora of mice with that of humans caused profound changes in the metabolism of the mice, especially their bile acids. These acids emulsify dietary fat, thus increasing its absorption. As a result there was increased storage of fat in the liver, causing “fatty liver”, and increase in LDL cholesterol, the “bad” type.
A year later Nicholson and his colleagues published a follow-up study (January 15, 2008 issue of Molecular Systems Biology) in which they supplemented the mice who had “human” flora in their gut with Lactobacillus, a species of bacteria that is present in yogurt. The result? Within 2 weeks (!) they found profound metabolic changes in fatty acids and amino acids metabolism. The most notable effect was on bile acids: the Lactobacillus blunted the bile’s action in fat absorption.
This research, like any other significant scientific study, raises more questions than it answers. But the most pressing one is that which I raised above: How could a few billion bacteria affect so profoundly the metabolic profile on 100 trillion? And within 2 weeks?
To be honest, I don’t think there is an obvious explanation. Bacteria have been shown to exchange genes and thus acquire new traits quite rapidly. It is possible that the Lactobacillus genes spread like a wildfire through the existing flora. But this needs to be experimentally demonstrated.
But one could not escape the practical conclusion of this experiment: Yogurt (and other probiotic foods?) can cause a reduction in fat absorption, and this is of paramount importance in dieting and in the development of type 2 diabetes. It is also just a question of time before a sharp entrepreneur will publish a new diet book (the yogurt solution, or the probiotic zone, or may be the bacterial diet?) that will take the market by storm.