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How gut bacteria inhibit weight loss and what you can do about it

Bacteria are microscopic, single-celled organisms that live everywhere. And I really mean everywhere.

You can find bacteria in some of the world’s harshest environments: the upper atmosphere, the bottom of the ocean, in volcanoes, and Antarctica.

You can even find them in and on your body.

Bacteria colonize your stomach and intestines; you can find them on the surface of your skin and eyes; and you can even find them in your nose and mouth. Essentially, they’re everywhere.

The bacteria in your gut (your digestive tract) is a feature of human biology that, until recently, hasn’t been given very much thought.

Increased attention from the medical research community have taught us that the bacteria residing in the gut can have pretty important implications for your health. Some research even suggests gut bacteria are involved in weight loss and maintenance.

This article is going to explore the connection between the gut microbiome (an all encompassing word that refers to all the bacteria in your stomach, small intestine, and large intestine, collectively) and weight.

How gut bacteria influence your health

Part of the bacteria’s role in your gut is helping you digest food and turn it into nutrients that your body can use.

Bacteria influence your health through the substances that they make as a response to the food you eat. These substances can cross the barrier separating your gut from the rest of your body. Once they get into your blood stream they can influence your body chemistry and your health.

TMAO (trimethylamine-N-oxide) is a good example of this biology in action.

When you eat foods like red meat or eggs, bacteria in your gut make a chemical that crosses the barrier between your gut and your blood circulation.

Once that chemical is in your blood, it finds its way to the liver and is turned into a compound called TMAO. TMAO may help cholesterol build up in your blood vessels and contribute to heart conditions like atherosclerosis. Too much TMAO is also linked to chronic kidney disease.

Gut bacteria influence weight

Before we get to how gut bacteria influence weight, let’s quickly talk about how we know gut bacteria can influence weight.

Two studies in particular really highlight the connection.

The first was conducted by a researcher named Dr. Peter Turnbaugh, who now works as an associate professor at University of California San Francisco, but published a paper when he was a trainee in 2006 at Washington University in St. Louis Missouri.

In that study, Turnbaugh and his colleagues had three different types of mice.

The first were mice prone to obesity.

The second were mice prone to be lean.

The third group of mice were “germ free”. This means that they were raised in completely sterile conditions and, therefore, did not have any gut bacteria.

Part of the study was seeing what effect taking the gut bacteria from lean and obese mice had when they transferred them into the third group of mice, which had no gut bacteria.

When the researchers transferred the gut bacteria from lean mice to germ free mice, the mice stayed lean.

No surprising results there.

Interestingly, when the researchers transferred the gut bacteria of the obese mice to the germ free mice, they noticed an increase in total body fat!

There was something about the gut bacteria in the obese mice that transferred the ability to generate body fat to the germ free mice.

The second study linking gut bacteria and weight I’d like to mention was conducted a little more recently in 2013.

This one was published in the journal Science and the lead author was Dr. Vanessa Ridaura – who received her Ph.D. in the same lab at Washington University that Turnbaugh did.

In this study they used gut bacteria from human twins: one of the twins was overweight and the other was classified as lean.

When they put gut bacteria from an overweight twin into a germ free mouse, they found the mouse’s body weight increased and they gained more fat tissue.

These two studies very elegantly suggest a solid link between differences in gut bacteria composition between overweight and lean individuals and an observable effect on weight gain and fat tissue.

How gut bacteria influence weight

Now that we know there is a link between gut bacteria and weight, maybe you’d like to know how that connection works.

The 2006 study by Turnbaugh in mice showed that gut microbiota from obese and lean mice were different with respect to two dominant bacterial divisions: bacteriodetes and firmicutes.

Bacteriodetes is a pretty common phylum. Its species can be found distributed in the environment (the soil, sediments, and sea water) and it is extremely common in the guts and skin of animals.

Firmicutes is a phylum that makes up a large portion of the mouse and human gut microbiome.

What Turnbaugh and his colleagues noticed is that the slight shift in bacterial makeup of gut bacteria in lean and obese mice was associated with an altered capacity for energy harvest: gut bacteria in obese mice got more calories out of digested food than gut bacteria in lean mice.

What this study suggested is that obese mice had a higher caloric intake despite eating a similar amount of food. All because the gut bacteria processed food a little differently.

What this boils down to is:

Gut bacteria influence weight by controlling how many calories you extract from the food you eat.

What can you do to promote good gut bacteria?

Probiotic supplements are a good start. A person’s diet is the most important factor for altering the gut microbiome and you can find probiotic formulas specifically tailored for conventional or vegetarian diets.

Probiotics work by promoting the colonization of the good bacteria in your gut. For a little more help finding the right probiotic supplement, please contact me. I’d love to help you out.


As research advances, more is being learned about links between gut bacteria and the body. We’re learning that the microbiome influences diseases like diabetes, conditions like obesity, and even mental health.

Supplements that promote good gut health are now an important part of healthy living.

Sources and further reading

An obesity-associated gut microbiome with increased capacity for energy harvest

Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism in Mice

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