Thursday, September 12, 2013

How gut bacteria alter metabolism and how antibiotics help the bad guys.

Every week more and more studies get published on the bugs in your gut and how they can help, and harm, you.  This past week, 2 new studies were published that shed a little light on how these little guys affect health and how antibiotics help the bad guys take over.

In the first study researchers used the gut bacteria of human twins discordant for obesity.  This means that one was obese and the other lean.  They took the gut bacteria from each twin and implanted it in to mice that were bread to have sterile guts.  As one would expect, the mice who received gut bacteria from the obese twin grew larger and fatter than the mice implanted with the lean twin's bacteria.  This was primarily due to an increase in the amount of bacteroidetes species in the lean mice compared to the obese.  The researchers point out that this was not due to an increased consumption of food as both groups of mice ate the same amount of food.  The difference was due to the bacteria in the gut producing a metabolic profile more conducive to obesity.

One of the cool parts of this study was that the researchers didn't stop there.  Once the trial was over, they housed the mice together and followed them to see what happened.   Mice are known to swap bacteria pretty freely(AKA they eat each others' poop) and that is exactly what happened.  The interesting part is that the obese mice were protected from becoming obese by coming in to contact with the gut bacteria of the lean mice.  Specifically, bacteria of the species bacteroidetes were shown to help the obese mice by returning their metabolic profile to that of the lean mice.  However, this was only under specific dietary conditions.  When the obese mice were served a diet high in fruits, vegetables, and fiber and low in saturated fat, coming in to contact with the more health promoting bacteria allowed their gut to take on the more healthy metabolic profile.  However, when fed a diet high in saturated fat and low in fruits, vegetables, and fiber their metabolic profile remained obese suggesting they were not afforded the protection provided to them by having contact with the bacteria from the lean mice.

The other study looked at how a course of antibiotics can help the bad guys overtake the good guys.  In the first 24 hours after beginning a course of antibiotics, researchers noticed a surplus of sugars in the gut of mice.  They attempted to replicate the condition in mice bred to have sterile guts by introducing a pathogenic strain (Salmonella or Clostridum Difficile) with a beneficial strain (Bacteroides Theta).

B. Theta is known to liberate sugars found in the mucus of your intestinal tract but does not consume a specific type known to feed other types of bacteria, good and bad.  Since the pathogenic bacteria are unable to break down mucus themselves, it was theorized that they were feeding on sugars liberated from mucus by B. Theta.  In this simulation, B. Theta liberated the sugar but without the other beneficial bacteria to consume that sugar there was fuel for pathogenic bacteria which, when introduced in to the gut, proliferated and caused trouble.  If the mice did not come in to contact with the pathogenic the sugars in the gut went back to normal within three days, presumably as the good bacteria is restored and consumes the excess sugars.

These studies show how important the beneficial bacteria found in the gut are to health.  The first study confirms something I believe will be a major stumbling block for people hoping that their obesity will be cured by a fecal implant.  Without a diet that will provide an environment that is optimal for beneficial bacteria to live in, a fecal transplant will be a failed, short-lived solution.  In other words, you won't take a pill and be able to eat what you want, which is more than likely what people are waiting for.