DEAR DOCTOR K: Do the germs that live on or in us affect our health?
DEAR READER: Trillions of germs live in and on us, all of our lives. They live on our skin, in our mouth, in our digestive tract and elsewhere. In yesterday’s column, I mentioned that amazing recent discoveries have greatly expanded our understanding of these germs and the effect they may have on our health.
Only a few years ago we thought that most of the germs that live on or in us were not affecting our health in any way. We thought they were just along for the ride.
In the past few years, though, new technologies for identifying the germs that live on or in us, and for determining their genes, have produced astonishing results. (A gene is a stretch of DNA that makes a particular protein. Proteins are the workhorses that cause each cell in the body to function correctly.)
We’ve always assumed that it was our genes — the genes inside each of our cells — that define how we function in health and that produce many of our diseases. Many scientists have assumed that once we understood all of our genes and how they worked, we would understand human health and disease.
We humans have more than 20,000 different genes. Recently, we’ve learned that the bacteria that live on and in us have 5 to 8 million genes. Do the math: The microbes on and in us have nearly 400 times more genes than we do! The genes of all those bacteria and other microbes are collectively called the “microbiome.” Genes of the microbiome make proteins that enter our bodies and affect our body chemistry.
Here’s one example: We have different types of bacteria living in our gut. Many of them help us digest carbohydrates — to break them down into simple sugars. Those simple sugars enter our blood, and eventually travel to our cells to provide energy for them.
Some types of bacteria are very efficient at digesting carbohydrates: They produce more simple sugars. Other bacteria are less efficient. What might that mean? Well, if a person had relatively more of the efficient types of bacteria, they would produce more simple sugars — and therefore more calories. And that would mean a greater tendency to gain weight.
To make a long story short, there is growing evidence that the types of bacteria in our gut may be contributing to the obesity epidemic.
Research is also incriminating our gut bacteria in a remarkable spectrum of different diseases. These include Type 2 diabetes, inflammatory bowel disease, colon cancer, heart disease, psoriasis, non-alcoholic fatty liver disease, asthma and even autism.
This field of research is still in its infancy. We don’t know yet how much effect our microbiome has on our health. But a growing number of scientists think it could be profound.
Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.