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Simple test to determine if your gut contains fattening bacteria

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The following sample of research illustrates the connection between gut bacteria and obesity.

  • Research has found that the microbiota of the digestive system in lean individuals is different than that of overweight individuals. A review of one body of work that looked at a study of humans and one of mice both of whom underwent gastric by-pass surgery, postulated that 20% of the weight loss was from a change in the microbiota. When the microbiota from the mice was introduced into mice that had no gut microbiota, both groups of mice loss weight and had less fat than control mice.
  • Another study posted on found that when given microbes from an obese human, mice became obese. Findings showed that there are fattening microbes and thinning microbes and that the thinning microbes can overtake the fattening microbes when mice ate a diet that was high in fruits and vegetables and low in saturated fat.
  • The findings of a study from the Netherlands reported on two bacteria associated with obesity and thinness. Bacteroidetes bacteria were found to be more common in lean people while Firmicutes bacteria were more common in the obese people. When the obese people consumed a low calorie diet, "as they lost weight, they acquired Bacteroidetes and lost Firmicutes." When overfeeding both lean and obese individuals the "bacteria in the obese people didn’t change, but for the lean people their Firmicutes increased and their Bacteroidetes decreased. Firmicutes increased the absorption of calories eaten.
  • An animal study published in the Journal of Proteome Research, suggests that gut bacteria may play a role in obesity and delay weight loss by slowing down the activity of energy-burning brown fat.
  • In a study published in the journal Science and on the website, mice became obese when given human microbiome from obese humans but not when given human microbiome from lean humans. The bacteria in "lean mice digested more fiber, and gave off more short-chain fatty acids than the bacteria in the obese mice." Short-chain fatty acids are thought to cause "less fat to accumulate in fat cells, boost calorie burning, and increase satiety hormones." Click here to get details on this study.

This last study supports additional research that showed fattening bacteria are associated with slowing intestinal transit time, increase BMI, increase body fat and slowing weight loss. It also supports findings that the other fattening bacteria, like Methanobrevibacter smithii (M. smithii ) increase caloric harvesting (they get more calories out of the macro nutrients we eat) and by doing so, the additional excess calori needs are stored as fat. Other bacteria like Bacteroidetes are denied receiving and metabolizing those macro nutrients into usable energy. Macro nutrients include carbohydrates, proteins and fats, and it is the carbohydrates from which, M. smithii mainly harvest calories.


A simple breath test could reveal the presence of a disproportionate number of bacteria. Researchers from the Cedars-Sinai Medical Center in Los Angeles reported in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism that "people with high levels of both hydrogen and methane in their breath are more likely to have a higher body mass index (BMI) and a higher proportion of body fat."

A gut bacterium called Methanobrevibacter smithii (M. smithii ) help extract energy and nutrients from food (mainly sugar and other carbohydrates) and "are responsible for most of the methane produced in the human gut." The more M. smithii there is the more that alter the bodies energy balance and the more likely a person is to gain weight. Participants' tested were "more likely to have a higher BMI and higher proportions of body fat. when their breath had "higher levels of both methane and hydrogen."

The researchers noted that "This is the first large-scale human study to show an association between gas production and body weight," adding that "this could prove to be another important factor in understanding one of the many causes of obesity."

A Hydrogen breath test is also used in the clinical diagnosis of dietary disabilities such as fructose intolerance, fructose malabsorption, lactose intolerance and lactulose intolerance, and Helicobacter pylori or other Small Intestine Bacteria Overgrowth (SIBO) abnormalities.

Breath tests are also used to detect methane which could also indicate the presence of SIBO and malabsorption of sugars in the small intestine. There are patients who can suffer from the same malabsorption issues who produce relatively large amounts of methane but little or no hydrogen.

In some cases a more invasive procedure such as an endoscopy that reaches only the reaches into the top portion of the GI track or colonoscopy, that only reaches the end part, may be performed. However the remaining 17 feet is not accessible. Another test, esophagogastroduodenoscopy (EGD) may be performed by a gastroenterologist, if there are "symptoms that are new, cannot be explained, or are not responding to treatment,' including but not limited to bringing food back up (regurgitation), feeling full sooner than normal or after eating less than usual, Heartburn, pain or discomfort in the upper abdomen or swallowing problems or pain with swallowing. This test is also conducted for symptoms of weight loss that cannot be explained. During this procedure a Gastric tissue biopsy and culture samples of the stomach and part of the small intestine bacteria can be taken for analysis. It is also used in the diagnosis of Helicobacter pylori.

This information is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical/nutritional/fitness advice. Information presented is subject to change as additional discoveries are made or additional research is published.

Sources:, Science 341: 1079, 2013; American Association for the Advancement of Science,,,,,,,,,,



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