TEXT ON SCREEN: THERE ARE UP TO 100 TRILLION MICROBES LIVING IN THE HUMAN BODY.

ARE THEY MAKING US FAT?

STANFORD PROFESSOR JUSTIN SONNENBURG STUDIES THE MICROBIOME

JUSTIN SONNENBURG (ASSOCIATE PROFESSOR, STANFORD SCHOOL OF MEDICINE): We’ve had a new appreciation of a facet of our biology that we call the gut microbiota, this complex community of microbes that lives in our intestine. They’re connected to our metabolism, our immune function. There’s emerging evidence that these microbes may dictate aspects of moods and behavior, but if we don’t take care of this community or if something goes awry, the whole ecosystem can turn against us and actually contribute to health problems.

TEXT ON SCREEN: RESEARCHERS HAVE FOUND THAT THIN PEOPLE AND OBESE PEOPLE HAVE DIFFERENT MICROBES.

ONE EXPERIMENT FOUND THAT “OBESE” MICROBES SEEM TO LEAD TO WEIGHT GAIN.

JUSTIN SONNENBURG: Investigators decided to use germ-free mice to study the way that the gut microbiota contributes to disease. So the investigators took two groups of mice. They gave one group an obese microbiota, and another group of mice a healthy microbiota, and then they just gave them the same diet and asked whether the mice receiving the obese microbiota gained weight more rapidly, and indeed, they did.

TEXT ON SCREEN: SONNENBURG WORRIES THAT CHANGES IN OUR DIETS HAVE DAMAGED OUR MICROBES.

JUSTIN SONNENBURG: Microbes eat all of the nutrients that we haven’t absorbed in our digestive tract and that primarily is dietary fiber. What’s been really startling, if you look at the trend in dietary fiber consumption, is that it’s plummeting. What’s happening over time is that we’re losing microbial species in our gut, likely because we’re not feeding them properly, and this corresponds with all of these rising health problems.

There’s a bit of a chicken-and-egg problem of causality, so there needs to be very careful investigation to see whether the depleted microbiota is then leading to problems in our health, but I think a lot of arrows are pointing in that direction.

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