Do Your Gut Bacteria Influence Your Metabolism?
IRA FLATOW, HOST:
This is SCIENCE FRIDAY. I am Ira Flatow. Did you know that trillions of bacteria live in your gut, happily dining on the food you eat? And your bacteria community, well, it's different than mine; everyone has a different community and that is important because as a new study published in Science points out, the specific bacteria you shelter can alter your metabolism. It can help determine your health. How do you get the bacteria in your gut? What connection do they have to our well-being?
Jeffrey Gordon is a microbiologist and director of the Center of Genome Science and Systems Biology at the Washington University School of Medicine in St. Louis. He's also an author on that paper and he joins us from the studio at Washington University. Welcome to SCIENCE FRIDAY.
JEFFREY GORDON: Pleasure to be able to talk with you.
FLATOW: Thank you. Let's talk about the gut bacteria. You looked at gut bacteria and how it could transmit lean or obese traits. Tell us how you tested that.
GORDON: Well, we started out with twins, where one twin was obese and the other twin was lean. There's been a lot of work trying to understand how these trillions of organisms relate to our health status. So we did a test. We ask how much of the obese twin's weight and metabolism could be ascribed to their bacteria and we transplanted these bacterial communities into sterile mice.
We did the same thing for the lean twin and waited. Then we saw that the mice that had received the obese donor's gut community increased the amount of fat in their body, gained more weight and had some of the metabolic features associated with human obesity.
FLATOW: Wow. Could you reverse that?
GORDON: Well, that's a good question. So we tried to actually prevent this. We took the same approach, but soon after we transplanted the communities, we co-housed, put in the same cage, a mouse that had received the obese twin's community and a mouse that had received the lean twin's community. That's what we call the battle of the micro biota. And the presence - the presence of - it sounds very dramatic and the results were actually quite dramatic.
The obese community was transformed so that the mouse that harbored it began to acquire the features of the lean community. There was an invasion of microbes from the lean community in one of the mice into the community that harbored the obese community. That transformation prevented the development of increased body weight and fat content and eliminated the metabolic features associated with obesity.
FLATOW: So somehow then the micro biota, the bacteria were controlling metabolism?
GORDON: That's right. First of all, the remarkable things was that the invasion was one way. The lean bugs went into the obese community, transforming it, but not vice versa. And you're absolutely right. There were job vacancies in the obese community, openings that were filled by these organisms from a lean gut community.
FLATOW: And do we know the mechanism by how the metabolism was changed?
GORDON: Well, we know what functions certain groups of bacteria are responsible for because we actually took notice of who were the invaders. And it was that process of invasion by these groups of organisms that collectively are called the bacteroidedes(ph) that were associated with this prevention of the increased weight and metabolism.
We knew who the actors were, but we also asked the question, why isn't there an epidemic of leanness if these things can occur, at least in this setting.
FLATOW: And the answer is?
GORDON: Well, it's diet, diet, diet. The first battle of the micro biota was done with mice eating a standard mouse chow. Low in fat and high in plant fiber. So we tried to make the battle more realistic. Not only did we transplant human gut microbes into the recipient mice, but we also gave them human diets. Two different types of diets based on the types of diets we consume in America.
One diet representing a diet that was consumed by people who favored low fats and high fruits and vegetables in their daily menus, and just the opposite type of diet - high saturated fats, low in fruits and vegetables. So with the healthier diet, the invasion occurred, there was a prevention of the weight gain and the metabolic features I described, but that invasion and that prevention was not evident when the mice were consuming the high saturated fat diet.
So it's evident to us that these job vacancies can't be fulfilled unless the right diet is being consumed.
FLATOW: Is that because the bacteria prefer a high fiber diet like that to survive and so they'll populate more?
GORDON: That's the general idea. There are ingredients in the diet that the bacteria can utilize, can process in ways that help themselves as well as help us, and the diet and microbes collude, collaborate, the shape, the properties of these communities, and affect us.
FLATOW: What about other things? Since it's controlling metabolism, what about other things that are going on in the body? Are they influenced also?
GORDON: Yes. And I think you're alluding to the fact that obesity is a very complex puzzle with lots of parts - how much food we consume, how much exercise we do each day. The question was, could our microbial communities, which are tasked with the responsibility of transforming the foods that we eat into metabolic products that shape our biology and our biological differences, what role do they play?
FLATOW: Yeah. Well, if you know what bacteria makes you lean and you know how to feed them the right food, why can't we all start that diet and find a probiotic that would work that way and lose weight and get healthier?
GORDON: Well, let me answer that question in a couple of ways. By probiotic you're referring to a different type of probiotic, not the type of probiotics that are present in fermented milk products that everybody is most familiar with. But we're talking about organisms that are naturally occurring, that have adapted to life in our gut, that haven't been genetically modified. We're looking for those creatures that we want to give.
And yes, we have to figure out which one of these groups of bacteria are most helpful in different populations of people. That's one test. And then to match the diet with their capacity. So we can't think of food in a way that's divorced from the microbes that live in our guts.
FLATOW: So it's not as easy as hanging out with leaner people and you might get some of their bacteria that you might like to make you lean? Could it be that easy?
GORDON: Well, it would be useful to look at the lifestyles of lean individuals, but at the same time, yes, it's not easy, but there is hope. And I think that these types of experiments point to another facet of our biology that we might be able to manipulate intentionally in ways that could enforce health and perhaps at very early stages of our lives.
FLATOW: So there is an environmental influence outside the body and something that's in your family perhaps that could be affecting the bacteria.
GORDON: Well, we also know that obesity is associated with a less diverse microbial community. That goes back to this concept of job vacancies. Are there vital functions that aren't represented in the microbiota of an obese individual.
FLATOW: So that's...
GORDON: So the answer is yes.
FLATOW: Yeah, so I remember reading research about that, that the more diverse your bacteria are, the better it is.
GORDON: That's exactly right. And of course, what kind of foods should we create to help cultivate this microbial garden?
FLATOW: You know, this is what foodies like Michael Pollan and people have been saying now for a long time, that if you get, you know, these complex foods that you eat, they're going to be feeding those gut bacteria.
GORDON: Exactly. And we can't think of the value of foods independently of the microbes that we harbor. And we have to think of the consumer's microbial communities. I think that offers a great deal of opportunity to design foods from the inside out, not just from the outside in.
FLATOW: So what's your next step here?
GORDON: A couple of things. Number one, to see which microbes function as invaders but where the donors of these communities represent different ages, different cultural traditions, different lifestyles. To really hone in on whether there's a set group of microbes that can fulfill functions of the type we elude to or whether we're going to have to customize these groups of microbes. That's step one.
The other step is to see what we can do with our existing diets to remove or add ingredients that may support the important health-promoting activities that these microbes we talk about.
FLATOW: You know, it almost seems like this whole field of the microbiota, the bacteria in your gut is just now just — use a bad phrase - exploding. You know, the research in the news that's coming out as if we discovered something new.
GORDON: And of course it's as old as microbiology and as old as us. I think that the ability to describe differences between microbial communities and healthy and diseased populations is one important step. And that's been very stimulating and very enticing. The challenge, as illustrated by this study, is to actually set up systems to test whether these differences are cause or effect. And here we have evidence for cause, and that's helpful.
FLATOW: So should - how transferable is this stuff from mice to people yet?
GORDON: Well, that's an excellent question. Of course the mice are designed to incorporate the features of the very human population that we want to help. So it's that population's microbes that are installed into the guts of these sterile mice. And it's their diets. So we try to anticipate how to translate this information to the very humans that supply the microbes and the foods that help us construct these models.
FLATOW: So we're just beginning down that road to figure this out. Yeah, all right. Well, thank you very much, Dr. Gordon. This is quite fascinating and it's something we can all relate to.
GORDON: Bon appetit.
FLATOW: Go for those — so the take-home message is go for that high fiber, high fiber diet to feed the biome there.
GORDON: And you never dine alone.
FLATOW: You're not eating, you're not eating for one. Your turn. All right. Dr. Jeffrey Gordon is a microbiologist and director of the Center of Genome Sciences and Systems Biology at Washington University School of Medicine in St. Louis. We're going to take a break and when we come back we're going to talk lots more about, well, a search for life on earth by looking at Mars. Could we all be Martians in origin? Interesting stuff coming up after the break, so stay with us.