It is generally assumed that it is the breakdown products of digestion (fats, sugars, and proteins) that are absorbed provide the energy for our cells and the raw materials for repair of injured tissues. But we are now finding that some of what we eat makes it to the colon where it is modified by bacteria before being absorbed. And those products of bacterial metabolism are also a key part of keeping us healthy.
Microbiome--a word most of us could not have defined 10 years ago--is now encountered daily on television, in newspaper articles and in advertisements for probiotic containing yogurts.
So, what is this mysterious microbiome? It is the collection of organisms (really an interactive community) that live on and in our bodies and includes all the bacteria, viruses and fungi that live on our skin, in our nose, our mouths and in our digestive tract. It is a diverse community calculated to consist of more than 10,000 unique microbial species.
Investigation of the microbiome has made huge strides using the same genetic techniques that have sequenced the human genome. PCR (polymerase chain reaction) is a tool that can rapidly identify and catalogue the entire collection of organisms that is unique to each of us.
How big is the microbiome? It has been estimated that 9 out of 10 of the cells in our body are microbiome organisms while just 1 of 10 are truly “us,” the cells whose DNA we inherited directly from our parents. But because bacteria are small compared to human cells, these organisms comprise only 3 percent of a body's total weight (2 to 6 pounds in a 200-pound adult).
The types and numbers means that microbiome organisms vary from person to person, and can change quite quickly depending on our diet and any medications we might be prescribed.
One study on the effect of diet on the microbiome compared the bacterial balance in the large intestine (colon) in three discrete groups - one on a full vegetarian diet, another on an unlimited animal product diet, and a third group that ate meat just once a week. The colon bacteria ratio in all three groups remained stable over time with the ratio of bacteria in the “meat once a week” group intermediate between the two extremes.
A recent study demonstrated how quickly a change can happen. Researchers looked at two groups: 1) Those on a plant-based diet rich in grains, beans, fruits and vegetables and 2) A second group on an animal-based diet of meats, eggs and cheeses.
Researchers again found a stable (and similar) bacterial population in each group, but in addition demonstrated that when a traditional vegetarian was changed to an animal-based diet, the ratio of bacteria could in just four days.
The bacteria, fungi and viruses that make up our microbiome can impact our health in two ways.
First, this stable community of thousands of organisms can help prevent infection with disease causing bacteria. It is thought that the microbiome controls the real estate, so to speak, and thus “crowds out” undesirable bacteria. When you take antibiotics, this balance can be upset, a niche for new bacteria opens up the chances of developing a colon infection with a new bacteria (C. Difficile Colitis is one example) increases.
The treatment? A targeted antibiotic specific for C Difficile which allows the normal microbiome to reestablish itself. With sensitive genetic testing, the C Difficile can still be detected in small numbers in some patients, but they are now held in check by the “good” bacteria.
The moral to this story is that you want to minimize antibiotic (and other unneeded medication) use as much as possible.
A second--and until recently less appreciated--health benefit results from our body absorbing and then utilizing the products of microbiome metabolism.
The food we eat is never completely absorbed in the upper digestive tract, and fiber (which is not easily digested) as well as a small amount of the proteins, fats and carbohydrates make their way to the colon where they are used as nutrition by the colon bacteria. It is these final products of their energy metabolism that are absorbed by the colon.
These “leftover” molecules that are absorbed through our skin or lining of the digestive tract provide their health benefits via their influence our daily metabolism or by modifying the effectiveness of medications we might be taking.
I suspect you have heard the phrase “we are what we eat.” That would assume that our health and our diet are interrelated. But now we have learned that it is more complex than just the direct effects of proteins, sugars and fats that are used by our bodies for energy and healing. Our health is also impacted by molecules produced by our microbiome.
We will review a few specific examples of how the microbiome can impact our health in my next column.