July 4, 2013 at 2:44 PM ET
The germs living inside you, which scientists now believe can affect your weight, your risk of disease and other factors, may be shaping your health your whole life long, researchers reported on Thursday.
While the study doesn’t answer the question of whether you can change this so-called gut microbiome and lose weight, it does suggest a once-a-year stool test might become part of your regular checkup, the researchers say.
They did some in-depth, long-term studies on the bacteria living inside several dozen volunteers and found very little change over the years, with one notable exception: in women who lost a lot of weight suddenly.
“These results reveal that the majority of the bacterial strains in an individual’s microbiota persist for years, and suggest that our gut colonizers have the potential to shape many aspects of our biological features for most and in some cases all of our lives,” Jeffrey Gordon of Washington University in St. Louis and colleagues write in their report, published in the journal Science.
Every human carries pounds of microorganisms that we couldn’t live without. They break down food, prevent infections and extract nutrients like vitamin K for us. Microbes outnumber human cells by a factor of at least 10 to one and scientists believe at least 10,000 different species live in and on us.
Some studies also show they may affect our weight, by either pulling every last calorie out of food, or passing it along quickly before the body absorbs too many calories. They also probably affect diseases such as Crohn’s disease and irritable bowel syndrome.
Gordon’s team wanted to see if the makeup of various bacterial species changes over time, so they sampled the stool of 37 healthy Americans, including 33 who gave samples multiple times over more than five years, and four tested while on a liquid diet over eight months.
They developed a new type of genetic testing to monitor the different species of bacteria. As other tests have found, each person has a unique population of bacteria, although closely related people often share some of the same species.
There were a few changes, they found. “Nonetheless, the set of microbial strains was remarkably stable overall, with more than 70 percent of the same strains remaining after one year and few additional changes occurring over the following four years,” they wrote.
You might not think this, they noted.
“The objects we touch and consume during the course of our lives are covered with diverse microbial life,” they wrote. “Despite this (the genetic sequencing) revealed that on average 60 percent of the approximately 200 microbial strains harbored in each adult’s intestine were retained in their host over the course of a five-year sampling period.”
This finding “suggests that the majority of strains in the microbiota represent a stable core that persists in an individual’s intestine for his or her entire adult life, and could represent strains acquired during childhood from parents or siblings.”
So can diet, or perhaps a bad bout of diarrhea, change this balance? Four of the volunteers, who were obese, volunteered to go on a series of diets while having their bacteria sampled. In these four, the types of species changed a lot as they lost weight on a liquid diet and then went on a different diet to stabilize their weight.
There were certain groups, or genuses, of bacteria that thrived or whose populations plummeted on the weight loss diet, the researchers said. And the changes seemed more linked with the actual weight loss itself than the ingredients in the diet milkshake.
This needs more study – researchers aren’t sure yet which bacteria might help keep people at a healthy weight, or even if it’s possible to change people’s gut bacteria and help them lose weight.
Right now the findings point to a kind of founder effect for gut bacteria, Gordon’s team said. “Earlier colonizers, such as those acquired from our parents and siblings, have the potential to provide their metabolic products and exert their immunologic effects for our entire lives,” they wrote.