Your gut's what you eat, too

January 3, 2014 by Peter Reuell, Harvard Staff Writer

As the saying goes, you are what you eat. But new evidence suggests that the same may also be true for the microbes in your gut.

A Harvard study shows that, in as little as a day, diet can alter the population of in the gut—particularly those that tolerate bile—as well as the types of genes expressed by .

"What we are really excited about is we and others have shown in animal models that diet can rapidly have major effects on the microbes that are in the gut," said Peter Turnbaugh, a Bauer Fellow at the Center for Systems Biology in the Faculty of Arts and Sciences. He is senior author of the paper, which appeared in Dec. 11 edition of the journal Nature.

"But it still wasn't clear how fast the microbes in the human gut respond to changes in diet, and to what degree those changes would be similar in different people. This study is really the first time we've seen that, over the course of days, a new diet can reshape the microbial community, and that those changes are consistent and reversible."

As evidence mounts that the gut microbiome not only plays a role in digestion but may also affect overall health, Lawrence David, the paper's first author and a former junior fellow at Harvard's Society of Fellows who was recently appointed an assistant professor at Duke University, said the ability to manipulate those populations may offer new avenues for treating certain conditions.

"That's part of the excitement of this work: that the gut microbiome in humans responds to changes in diet on a much shorter timescale than people thought," David said. "That suggests it's at least feasible to—through host action—alter the gut microbiome, so we see this as establishing the dynamic range for those changes, and the amount of latitude individuals have in potentially altering it."

Researchers recruited 11 volunteers for the study, which began by collecting baseline data on each participant's gut microbiome. For four days, they ate their normal diets and kept logs detailing everything they consumed.

Following the baseline period, each spent five days eating a that consisted of granola, meals made with rice, onions, tomatoes, squash, garlic, peas, and lentils, with banana, mango, and papaya as snacks.

Just as on their regular diets, the participants kept daily food logs and collected samples to track how the microbes in their gut changed. After five days, they returned to their regular diets for a six-day "washout" period, to determine how quickly their microbiome would recover from any shifts caused by the food they digested.

Each then spent five days eating a diet composed of animal products, including bacon and eggs for breakfast, pork ribs and beef brisket for lunch, and salami, prosciutto, and a selection of cheeses for dinner. Snacks included string cheese, salami, and pork rinds.

Using samples collected by participants, "we saw changes in the abundance of different bacteria in as little as a day after food made it to the gut on the animal-product diet," David said. "On both diets, we saw significant changes in the types of genes that bacteria were expressing, as well as changes to the metabolic byproducts of bacterial activity—like short-chain fatty acids—about three or four days after they switched diets."

While the study results show that diet can affect the makeup of the gut microbiome, they also suggest that those changes may have very real implications for human health.

Though he stressed that the finding was still preliminary, David said Bilophila, a bacteria known to cause colitis in mice, was among the gut species that saw the largest population increases among people on the animal-product diet.

Earlier studies had shown that, in mice, diets high in milk fat increased the production of bile, which in turn led to increases in Bilophila. David and colleagues believe the increases in Bilophila seen in the current study may be tied to the cheese included in the animal-product diet.

"We did not set out to look for this, but when we asked which bacteria had the most significant increases, it was at the top of the list," he said. "We can't conclude from this study whether or not Bilophila might be causing colitis in humans, but our data does show that this colitis-associated bacteria can be enriched through diet."

The findings, David said, could point to a day when dietary changes could be used to treat certain medical conditions, rather than drugs or even surgery.

"That's part of the promise of this field, that we might somehow be able, through an altered or behavior, to shape the microbiome to improve health," he said. "People often refer to the microbiome as the 'second genome'—the first being our own—but what's interesting is that this second genome is potentially plastic and responsive to the way we choose to live our lives."

Explore further: Gut bacteria shift quickly after changes in diet, study shows

Related Stories

Gut bacteria shift quickly after changes in diet, study shows

December 11, 2013
(HealthDay)—If you were to switch from vegetarianism to meat-eating, or vice-versa, chances are the composition of your gut bacteria would also undergo a big change, a new study suggests.

Genetic makeup and diet interact with the microbiome to impact health

September 25, 2013
A Mayo Clinic researcher, along with his collaborators, has shown that an individual's genomic makeup and diet interact to determine which microbes exist and how they act in the host intestine. The study was modeled in germ-free ...

Gut microbes may be a risk factor for colorectal cancer

December 6, 2013
In one of the largest epidemiological studies of human gut bacteria and colorectal cancer ever conducted, a team of researchers at NYU Langone Medical Center has found a clear association between gut bacteria and colorectal ...

Your gut bacteria may predict your obesity risk

August 28, 2013
(HealthDay)—Bacteria in people's digestive systems—gut germs—seem to affect whether they become overweight or obese, and new research sheds more light on why that might be.

Recommended for you

Molecular hitchhiker on human protein signals tumors to self-destruct

July 24, 2017
Powerful molecules can hitch rides on a plentiful human protein and signal tumors to self-destruct, a team of Vanderbilt University engineers found.

Researchers develop new method to generate human antibodies

July 24, 2017
An international team of scientists has developed a method to rapidly produce specific human antibodies in the laboratory. The technique, which will be described in a paper to be published July 24 in The Journal of Experimental ...

New vaccine production could improve flu shot accuracy

July 24, 2017
A new way of producing the seasonal flu vaccine could speed up the process and provide better protection against infection.

A sodium surprise: Engineers find unexpected result during cardiac research

July 20, 2017
Irregular heartbeat—or arrhythmia—can have sudden and often fatal consequences. A biomedical engineering team at Washington University in St. Louis examining molecular behavior in cardiac tissue recently made a surprising ...

Want to win at sports? Take a cue from these mighty mice

July 20, 2017
As student athletes hit training fields this summer to gain the competitive edge, a new study shows how the experiences of a tiny mouse can put them on the path to winning.

'Smart' robot technology could give stroke rehab a boost

July 19, 2017
Scientists say they have developed a "smart" robotic harness that might make it easier for people to learn to walk again after a stroke or spinal cord injury.


Adjust slider to filter visible comments by rank

Display comments: newest first

2 / 5 (1) Jan 03, 2014
This is sort of pop science du jour, but All the more reason to moderate our medical use of antibiotics, despite custom, expectation, and marketing pressures.
5 / 5 (1) Jan 03, 2014
This article is not really about antibiotic use (although it's overuse is rampant and bad).
This article is very important. I wish they had included a test of a sugary diet. Some think that is the biggest culprit.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.