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  • Writer's pictureDoug Toal

The Influence of Gut Bacteria

Do you realize that each of us have approximately 30 trillion human cells in our bodies and that our cells are slightly outnumbered by the microorganisms that live in and on our bodies? In fact, the average person carries approximately 40 trillion microorganisms weighing three pounds, roughly the weight of your brain and little lighter than your liver. What’s more, every single member of your personal microbial community of 40 trillion microorganisms has an agenda. That’s right, you heard correctly. The 40 trillion cells that reside inside your body (primarily within your large intestine) have the instinct to thrive and flourish and I can tell you that they do not particularly care about your personal well-being and fitness.

Right about now, you might be thinking back to your high school biology class and remembering that bacteria and other microorganisms are single-celled and you may be doubtful that these simple creatures have the wherewithal to even have an agenda. Well, all I have to say is that scientists have come a long way in recent years in understanding how microorganisms communicate and work together. Many microbiologists have been busy decoding the secret language that bacteria use to communicate to each other and other species. In my own original work, I studied how a soil bacterium communicates with other members of its species in order to cooperate in food gathering and other social activities. This work and other scientific research has shown that bacteria are masters at presenting and secreting signal molecules to communicate to other bacteria and even to our own cells. Thus far, science has only scratched the surface in understanding and translating the ancient language of molecular signals but it is turning out that the microorganisms in our gut have a lot to say to our body and what they say matters more than we may know.

For instance, some experts believe that our cravings for certain types of sugary and fatty food may be partially instigated by molecular signals generated from microorganisms in our gut (more on that later). I don’t know about you, but the idea of bacteria in my gut manipulating the biochemical and hormonal pathways in my body to cause me to desire certain foods for their benefit and at my expense is very disconcerting. I realize that the idea of invisible creatures in our bodies telling us what to eat and how to feel is a little creepy. Keep in mind however that bacteria have been working inside the human gut for eons; digesting foods and providing nutrients that we ourselves cannot manufacture and we cannot survive without them. During these eons of cohabitation with the human host, our gut microorganisms have also developed tools to directly interact with elements of our neurophysiological system in a manner that may cause manipulation of host behavior.

An extreme example of microorganism manipulation of host behavior is seen when rodents become infected by a parasitic protozoan named Toxoplasma gondii. When this particularly nasty microorganism infects rodents it releases molecular signals to the rodent brain that cause decreased aversion to the scent of cat urine. Of course, this behavior is suicidal for the rodent. However, since cats are the only host within which T. gondii are able to sexually reproduce to begin its lifecycle, it makes perfect sense that the parasite should manipulate the unsuspecting rodent in a manner that ensures its survival within the feline host, even at the expense of the rodent.

Admittedly, the above example is extreme to say the least and is only included here as a way to demonstrate that microorganisms have the wherewithal to influence host behavior for their own benefit. But let’s bring it closer to home and take a look at why and how the microorganisms in our gut manipulate us into eating what they want rather than what we need.

In order to survive, the microorganisms in our intestines have developed sophisticated mechanisms to outcompete their neighbors for available food resources. Mounting evidence in scientific literature suggests that one particularly abhorrent strategy that microbes use involves the manipulation of our eating behaviors in order to increase their fitness at our expense. It appears that they may do this by manufacturing molecular signals that interact with our neurophysiological systems to cause us to crave food that they specialize on or foods that suppress their microbe competitors.

Recent studies also point to the possibility that microbes are able to induce dysphoria, which is a fancy word for general unease or dissatisfaction with life, until we eat foods that enhance their fitness. Perhaps this explains why many of us struggle with emotional eating leading to junk food binges and brings new meaning to the concept of “comfort food”. How many times have we all committed to a heathy diet only to be confounded by a lack of “self-control” resulting in binges on ice cream and fudge brownies? But what if science ultimately proves that our lack of “self-control” in these cases is really caused by the selfish whims of a few bad actors living within our intestines? If true, wouldn’t you want to do everything in your power to take back control of your eating habits?

Until science works out these details, one of the best ways to ensure that your gut microbiota send healthy signals to your body is to cultivate a diverse population of microorganisms. There are anywhere from 100 to 1,000 different species of bacteria that live in the human gut and scientific studies have shown that people with obesity and metabolic disease have a lower diversity of species in their digestive system. Some scientists have theorized that an increase in microorganism diversity in the gut promotes an environment where microbes must compete with each other for available food sources and that’s a good thing. On the other hand, a less diverse microbial population is likely to possess single species that have large population sizes and can expend resources to manipulate our body’s cravings in order to get more of the food that they desire.

So, what is the best way to promote a diverse gut microbiota? Put simply, you need to eat a diverse diet containing plenty of washed fruits and vegetables that contain prebiotic fiber and environmental microbes. I also believe that it is important to consume high quality probiotic supplements on a daily basis with a diverse set of beneficial bacteria to keep the bad actors in check. In addition, eat probiotic containing foods such as yoghurt, kefir, and fermented vegetables (at least three servings per day). And stay away from sugary foods and drinks since the bad microorganisms in your gut thrive on these unhealthy foods.

Other Resources:

· Noris, V., Molina, F., Gewirtz, A. T. 2013. Hypothesis: bacteria control host appetites. J. Bacteriol. 195: 411-416.

· Le Chatelier, E., Nielsen, T., Qin, J., Prifti, E., et. al. 2013. Richness of human gut microbiome correlates with metabolic markers. Nature 500: 541-546.

About the author:

Douglas Toal, PhD is a Clinical Scientist with extensive knowledge and expertise in medical laboratory sciences and metabolism and anti-aging medicine.

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