Obesity Problem Answer Might Be in the Bugs in Our Stomachs

Microbes can influence mood, food choice, maybe how we think, and make us fat.

August 24, 2014, 6:26 AM
PHOTO: A young woman chooses between an apple and a burger in this undated file photo.
A young woman chooses between an apple and a burger in this undated file photo.
Getty Images

— -- Scientists conducting a series of experiments in Sweden over the past five years have made a discovery that could make a profound contribution to the fight against global obesity.

The scientists, led by Fredrik Backhed of the University of Gothenburg, were studying mice that had been raised in a germ-free environment, and were thus lean and healthy. But when they were fed a "fecal pellet," which is just what it sounds like, from an obese human the mice quickly became obese, although exercise and their food availability remained unchanged.

All it took was a dose of microbes from the gut of an overweight human to make the mice prefer the fattier and sweeter morsels over the healthier foods.

After analyzing that, and numerous other recent experiments, scientists from three universities have made a bold proposal:

The single-celled organisms that live in our guts and help us digest our food and fight off diseases may have ulterior motives. Maybe they want to be in charge.

Not just of our gastrointestinal track. They want control of our diets, even if that makes us fat and unhealthy, they want to move our lives in directions that are good for them even if bad for us, and they may even want to take over our brains.

In fact, they may have already done that.

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Is it possible that the bacteria we depend on in the symbiotic relationship between us and them are clever enough to make us love the taste of seaweed?

Well, that's already history, at least in Japan.

"That's the science fiction part of this," evolutionary biologist and psychologist Athena Aktipis said in a telephone interview. "But I think it's really compelling."

Aktipis, who is now with Arizona State University, began an intriguing research project while she was at the University of California, San Francisco.

Joined by colleagues Carlo C. Maley of UCSF and Joe Alcock of the University of New Mexico, Albuquerque, the trio set out to see if evidence in the scientific literature supports the idea that our bodies may indeed be at war with our own guts, even over control of our brains, and whether that would partly explain the obesity epidemic that is sweeping much of the world.

This is new stuff. We've known for many years that we have good bacteria and bad bacteria in our guts, some helping and some hurting as we move through life, but recently experts have begun wondering if that's all there is to it.

Does some of that bacteria in your gut fight to serve its own agenda to meet its own needs, not those of their host -- which is you?

How could something that small be a threat? They may be tiny, but your gut is home to trillions. You are one individual, and their genes outnumber yours 100 to one.

They have access to the vagus nerve, which connects 100 million nerve cells in the gut to the base of the brain. They can influence our sense of taste, they can produce toxins to make us feel bad, and they can put is in a good mood, wanting more of whatever they need for themselves.

The researchers have put together a plausible argument, published in the journal BioEssays, suggesting that's exactly what's happening, even if it sounds like science fiction.

But they also argue that we could turn this thing around and put ourselves back in total control, curing illnesses and making us much healthier along the way.

The microbes constitute "a whole ecosystem, and it's evolving on the time scale of minutes," Maley said in releasing the study. Just changing the diet can alter the entire colony of microbes, called the "microbiome," in 24 hours, he said.

The scientists are building on research by others suggesting we have a war going on in our guts.

  • Microbes can affect behavior in vertebrates, as evidenced by research showing one species of microbe "suppresses rats' normal fear of cat smells, often to the detriment of the rats, but to the benefit of the microbes that are ingested into their new feline host," the study says.
  • Many bacteria found in the human gut can manufacture dopamine, the feel-good hormone linked to drug and alcohol addiction, so they can have a dramatic impact on moods. Other microbes can make us crave fats and sugars, contributing to obesity.
  • "Specialist microbes that digest seaweed have been isolated from humans in Japan," the study notes. "African children raised on sorghum have unique microbes that digest cellulose." So some microbes know what they need and may change their host's taste to be sure they get it.

The list goes on and on, sometimes disturbingly.

It's possible that "the obesity epidemic could be contagious as a result of obesity-causing microbes transmitted from person to person," the study says.

That might partly explain why obesity affects entire families, and close friends. The microbes might do that by generating a preference for foods rich in what the microbes are seeking, like fats and sugars.

At this point, the conclusions by the researchers are still in the theoretical stage, but that may change quickly.

"This has been really a blind spot because we tend to think about our bodies as made up just of ourselves," Aktipis said, but a large amount of work in the last five years has been devoted to the possible split-personality of the human microbiome.

We have known for many years that the universe of tiny critters in our guts play an important role in human health, both for good and bad, "but the idea that it would be playing an active role where there would be different interests in different species of microbes competing with us is a new way to think about the nature of our bodies," Aktipis added.

It may not take much to nail this down. The contents of the human gut can be determined through several non-invasive techniques. A mouth swab tells which microbes are at work there.

For researchers who want the "big picture," a stool sample would work, although as Aktipis noted, "some people don't like the idea of giving up their poop."

Physicians treat obese patients all the time, so why not determine the composition of their entire microbiome at the same time? That data from across the country could be fed into a data bank telling which microbes are associated with which public health issues. In time we would have a much better idea of who the enemies are.

After all, this is warfare.

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