News / Health

After Weight-loss Surgery, New Gut Bacteria Keep Obesity Away

FILE - An overweight woman sits on a chair in Times Square in New York, May 8, 2012.
FILE - An overweight woman sits on a chair in Times Square in New York, May 8, 2012.
The logic behind weight-loss surgery seems simple: rearrange the digestive tract so the stomach can hold less food and the food bypasses part of the small intestine, allowing fewer of a meal's calories to be absorbed.

Bye-bye, obesity.

A study of lab mice, published on Wednesday, begs to differ.

It concludes that one of the most common and effective forms of bariatric surgery, called Roux-en-Y gastric bypass, melts away pounds not - or not only - by re-routing the digestive tract, as long thought, but by changing the bacteria in the gut.

Or, in non-scientific terms, the surgery somehow replaces fattening microbes with slimming ones.

If that occurs in people, too, then the same bacteria-changing legerdemain achieved by gastric bypass might be accomplished without putting obese patients under the knife in an expensive and risky operation.

"These elegant experiments show that you can mimic the action of surgery with something less invasive," said Dr. Francesco Rubino of Catholic University in Rome and a pioneer in gastric-bypass surgery. "For instance, you might transfer bacteria or even manipulate the diet to encourage slimming bacteria and squelch fattening kinds," said Rubino, who was not involved in the study.

Fattening Bugs, Slimming Bugs

For many obese patients, particularly those with type 2 diabetes, gastric bypass has succeeded where nothing else has. Severely obese patients routinely lose 65 to 75 percent of their excess weight and fat after the operation, studies show, and leave their diabetes behind.

Oddly, however, the diabetes remission often occurs before significant weight loss. That has made bypass surgeons and weight-loss experts suspect that Roux-en-Y changes not only anatomy but also metabolism or the endocrine system. In other words, the surgery does something besides re-plumb the gut.

That "something," according to previous studies, includes altering the mix of trillions of microbes in the digestive tract. Not only are the "gut microbiota" different in lean people and obese people, but the mix of microbes changes after an obese patient undergoes gastric bypass and becomes more like the microbiota in lean people.

Researchers did not know, however, whether the microbial change was the cause or the effect of post-bypass weight loss.

That is what the new study, by researchers at Massachusetts General Hospital and Harvard University, set out to answer.

They first performed Roux-en-Y on obese mice. As expected, the animals quickly slimmed down, losing 29 percent of their weight and keeping it off, the researchers report in the journal Science Translational Medicine.

To make sure there was not something about the general experience of surgery, rather than gastric bypass specifically, that affected the animals, the scientists performed "sham" Roux-en-Y on other obese mice. In this procedure, the researchers made incisions as if they were going to do a gastric bypass, but instead connected everything up as nature had it.

The researchers then transferred gut microbiota from the Roux-en-Y mice to microbe-free obese mice. Result: the recipient mice lost weight and fat - no surgery required. Crucially, obese mice that received gut bugs from mice that had received sham Roux-en-Y, not the real thing, did not slim down.

It is the first experimental evidence that changes in the gut microbiota cause the weight loss after gastric bypass, and that the new, post-bypass mix of microbes can cause weight loss in animals that did not have surgery.

In particular, just a week after surgery the Roux-en-Y mice harbored relatively more of the same types of bacteria that become more abundant in people after gastric bypass and that lean people have naturally.

"The effects of gastric bypass are not just anatomical, as we thought," said Dr. Lee Kaplan, senior author of the study and associate professor of medicine at Harvard Medical School. "They're also physiological. Now we need to learn more about how the microbiota exert their effects."

Slimming bacteria work their magic in either of two ways, studies of gut microbiota show. They seem to raise metabolism, allowing people to burn off a 630-calorie chocolate chip muffin more easily.

They also extract fewer calories from the muffin in the first place. In contrast, fattening bacteria wrest every last calorie from food.

Transferring slimming bacteria into obese people might be one way to give them the benefits of weight-loss surgery without an operation. It might also be possible to devise a menu that encourages the proliferation of slimming bacteria and reduces the population of fattening bacteria.

Another new study found that figuring out whether you have slimming microbiota or fattening ones might be as easy as breathing.

In a study published on Tuesday in the online edition of the Journal of Clinical Endocrinology & Metabolism, researchers at Cedars-Sinai Medical Center in Los Angeles report that people whose breath has high concentrations of both hydrogen and methane gases are more likely to have a higher body mass index and higher percentage of body fat.

Methane is associated with bacteria called Methanobrevibacter smithii, which in overabundance may cause weight gain by extracting calories from food super-efficiently, Cedars' Ruchi Mathur, who led the study, said: "It could allow a person to harvest more calories from their food."

The breath test could provide a warning that someone is at risk of obesity because he harbors fattening microbiota.

It could also validate what many overweight people have long suspected: if their slim friends eat two slices of bacon-cheeseburger pizza the 600 calories go through them like celery, but if the overweight person indulges then every calorie seems to turn into more fat. People absorb different quantities of calories from the exact same food, thanks to their gut microbiota.

You May Like

Video In US, Columbus Day Still Generates Controversy

Holiday marks date Columbus discovered Americas, but some are offended by legacy because he enslaved many natives he encountered More

Video Through Sports, Austria Tries to Give Migrants Traction

With 85,000 people expected to claim asylum in Austria this year, its government has made integration through joint physical activities a key objective More

Video Kickboxing Champion Shares Sport With Young Migrants

Pouring into Europe by hundreds of thousands, some migrants, especially youngsters, are finding sports a way to integrate into new host countries More

Featured Videos

Your JavaScript is turned off or you have an old version of Adobe's Flash Player. Get the latest Flash player.
Amnesty Accuses Saudi Coalition of ‘War Crimes’ in Yemeni
Henry Ridgwell
October 12, 2015 4:03 PM
The human rights group Amnesty International has accused the Saudi-led coalition of war crimes in airstrikes against Houthi rebels in Yemen. Henry Ridgwell reports the group says hundreds of civilians have been killed in strikes on residential areas.

Video Amnesty Accuses Saudi Coalition of ‘War Crimes’ in Yemen

The human rights group Amnesty International has accused the Saudi-led coalition of war crimes in airstrikes against Houthi rebels in Yemen. Henry Ridgwell reports the group says hundreds of civilians have been killed in strikes on residential areas.

Video No Resolution in Sight to US House Speaker Drama

Uncertainty grips the U.S. Congress, where no consensus replacement has emerged to succeed Republican House Speaker John Boehner after his surprise resignation announcement. Half of Congress is effectively leaderless weeks before America risks defaulting on its national debt and enduring another partial government shutdown.

Video New Art Exhibit Focuses on Hope

Out of struggle and despair often comes hope. That idea is behind a new art exhibit at the American Visionary Art Museum in Baltimore, Maryland. "The Big Hope Show" features 25 artists, some of whom overcame trauma and loss. VOA’s Deborah Block reports.

Video Columbus Day Still Generates Controversy as US Holiday

The second Monday of October is Columbus Day in the United States, honoring explorer Christopher Columbus and his discovery of the Americas. The achievement is a source of pride for many, but for some the holiday is marked by controversy. Adrianna Zhang has more.

Video Anger Simmers as Turks Begin to Bury Blast Victims

The Turkish army carried out new air strikes on Kurdistan Workers Party (PKK) targets on Sunday, a day after the banned group announced a unilateral cease fire. The air raids apparently are in retaliation for the Saturday bombing in Turkey's capital Ankara that killed at least 95 people and wounded more than 200 others. But as Zlatica Hoke reports, there are suspicions that Islamic State is involved.

Video Bombings a Sign of Turkey’s Deep Troubles

Turkey has begun a three-day period of mourning following Saturday’s bomb attacks in the capital, Ankara, that killed nearly 100 people. With contentious parliamentary elections three weeks away, the attacks highlight the challenges Turkey is facing as it struggles with ethnic friction, an ongoing migrant crisis, and growing tensions with Russia. VOA Europe correspondent Luis Ramirez reports.

Video Afghanistan’s Progress Aided by US Academic Center

Recent combat in Afghanistan has shifted world attention back to the central Asian nation’s continuing civil war and economic challenges. But, while there are many vexing problems facing Afghanistan’s government and people, a group of academics in Omaha, Nebraska has kept a strong faith in the nation’s future through programs to improve education. VOA’s Greg Flakus has more from Omaha, Nebraska.

Video House Republicans in Chaos as Speaker Favorite Withdraws

The Republican widely expected to become the next speaker of the House of Representatives shocked his colleagues Thursday by announcing he was withdrawing his candidacy. The decision by Majority Leader Kevin McCarthy means the race to succeed retiring Speaker John Boehner is now wide open. VOA National Correspondent Jim Malone reports.

Video German, US Officials Investigate Volkswagen

German officials have taken steps to restore some of the reputation their car industry has lost after a recent Volkswagen diesel emissions scandal. Authorities have searched Volkswagen headquarters and other locations in an effort to identify the culprits in the creation of software that helps cheat on emission tests. Meanwhile, a group of lawmakers in Washington held a hearing to get to the bottom of the cheating strategy that was first discovered in the United States. Zlatica Hoke reports.

Video Why Are Gun Laws So Hard for Congress to Tackle?

Since taking office, President Barack Obama has spoken out or issued statements about 15 mass shootings. The most recent shooting, in which 10 people were killed at a community college, sparked outrage over the nation's gun laws. But changing those laws isn't as easy as many think. VOA's Carolyn Presutti reports.

Video In 'He Named Me Malala,' Guggenheim Finds Normal in Extraordinary

Davis Guggenheim’s documentary "He Named Me Malala" offers a probing look into the life of 18-year-old Malala Yousafsai, the Pakistani teenager who, in 2012, was shot in the head by the Taliban for standing up for her right to education in her hometown in Pakistan's Swat Valley. Guggenheim shows how, since then, Malala has become a symbol not as a victim of brutal violence, but as an advocate for girls’ education throughout the world. VOA’s Penelope Poulou has more.

Video Paintable Solar Cells May Someday Replace Silicon-Based Panels

Solar panels today are still factory-manufactured, with the use of some highly toxic substances such as cadmium chloride. But a researcher at St. Mary’s College, Maryland, says we are close to being able to create solar panels by painting them on a suitable surface, using nontoxic solutions. VOA’s George Putic reports.

VOA Blogs