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Can't fit into your jeans? The problem may not just be your genes. It may also be the bacteria in your digestive tract.

Beginning in the United States, obesity has become a world-wide problem. There are many causes of obesity including, let's be honest, overeating, but Washington University (St. Louis) researchers in the USA have found the strongest evidence yet that bacteria in the small intestine and colon causes chronic weight problems.

Identical Twins with Different Gut Bacteria Gain Weight Differently

Dr. Jeffrey Gordon, director of the Center for Genome Sciences and Systems Biology at Washington University in St. Louis, led a research team that recruited four sets of identical twin women at locations around the world. One twin of each pair was thin, the other obese. The doctors then collected stool samples and transferred the bacteria, protozoans, and viruses the samples contain to mice that had been raised in a sterile environment.

Mice that received microbes from women who were obese became fat even though they were fed low-fat mouse chow. Mice that received microbes from women who were thin stayed thin on the same diet.

The difference between the two kinds of gut bacteria turned out to be their ability to digest sugars from fiber. The bacteria from women who were obese broke down various kinds of fiber into sugars. Some of the sugars find their way into the bloodstream of the mouse, or human, that hosts them. The bacteria from the women who were thin fed on the many of the same nutrients as their human or mouse hosts, and allowed fiber in food to pass undigested out the digestive tract.

Antibiotics Not the Solution for Weight Gain Caused By Bacteria

"It appears that certain bugs drive obesity," microbiologist Sarkin Mazmanian told the LA Times. If scientists could identify the single strain of bacteria most responsible for obesity, they could develop an antibiotic to kill it. 

Or, as Mazmanian and many other scientists point out, it may be that antibiotics fed to farm animals and prescribed too often in disease treatment are the basic problem. As antibiotics have been used over more and more of the world to help cows gain weight in feedlots or to keep chickens from catching infections while they live out their short lives in crowded cages, people over more and more of the world have been getting fatter and fatter.

There are many causes of obesity, but it may be that antibiotics have been killing the "good bugs" that have been keeping the "obesity bugs" in check. So what is an ordinary person to do with this information?

Bacterial Problem, Bacterial Rescue

Although most news accounts don't mention it, the researchers in Dr. Gordon's study didn't just find that "bad bacteria" caused weight gain. They also found that mice given bacteria from the thin women started to reverse weight gain.

The scientists reported that these "rescue bacteria" could rapidly turn around the ill effects of the obesogenic bacteria.

And earlier research has found that the bacteria that drive weight gain don't just break down fiber into sugars that provide extra calories. They cause inflammation that causes swelling. Up to 30% of the mass of fat around your waist or on your hips, and even more of the extra weight on your thighs, can be fluid and white blood cells generated by inflammation.

The good bacteria that can help you fight the obesity-causing bacteria are in the genus Bacteroides. These bacteria aren't added to most brands of yogurt, or at least they aren't yet. Your best bet for getting the healthy strains of Bacteroides is to eat brands of yogurt that are also available in Europe, such as Muller, distributed in the US by Quaker, Oikos, and FAGE.

  • Healy, M. Certain Bacteria May Ward Off Obesity. LA Times. 9 September 2013
  • Ridaura VK, Faith JJ, Rey FE, Cheng J, Duncan AE, Kau AL, Griffin NW, Lombard V, Henrissat B, Bain JR, Muehlbauer MJ, Ilkayeva O, Semenkovich CF, Funai K, Hayashi DK, Lyle BJ, Martini MC, Ursell LK, Clemente JC, Van Treuren W, Walters WA, Knight R, Newgard CB, Heath AC, Gordon JI. Gut microbiota from twins discordant for obesity modulate metabolism in mice. Science. 2013 Sep 6. 341(6150):1241214. doi: 10.1126/science.1241214. PMID: 24009397 [PubMed - in process]
  • Photo courtesy of Tobyotter on Flickr: