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Could Your Gut Bacteria Be Causing Your Weight Problem?

gut health microbiome nutrition prebiotics probiotics weight gain weight loss Dec 09, 2021

Could your poop be related to your weight?  It sure can.  Our knowledge about the microbiome is increasing day by day, and we are finding that it has a lot to do with our waistlines.   The microbiome refers to the bacteria that make up your gut and help you to digest your food.  We used to think that these microorganisms were separate from us, but now we are finding they are deeply connected with our biology.   We are actually composed of 10 trillion bacteria but only 1 trillion human cells!  You are more bacteria than human!  We have 23,000 genes but our gut carries over 3 million genes.  We have existed in a symbiotic relationship with these organisms since the beginning of humanity, but we have just now started to explore how they might affect our health.  We may be controlled by and rely upon them more than we realize, and they secrete many substances that modify everything from our mental health to our weight.  However, mainstream medical culture hasn’t quite caught onto the idea that we can manipulate the bacteria in our intestines to affect our a weight in a different way.  


What do we know about weight’s relationship to the bacteria in our gut? First of all, people who are heavier have a different composition of bacteria in their colons.  For starters, they have a decreased diversity of bacteria.  This means thinner people have a wider array of different types of bacteria.  Some of these bacteria that are more prevalent in obese individuals do bad things.  For starters, they can secrete inflammatory chemicals, and we are now learning that obesity is a disease of inflammation.  Also, studies in mice have found that if you take the bacteria (aka poop) from a fat rodent and put in into the gut of a skinny rodent that has been raised away from any sources of bacteria (I know….gross)…the mouse gets fat!  This shows that bacteria can actually control our weight without us even realizing it.  This is scary, but you should also feel relieved that it was not a lack of willpower on your part if you cannot lose weight.  It might just be those little friends that make you fat and make you fart! 

The two most common types of bacteria in our gut are called Bacteroides and Firmicutes.  It is important which bacteria you have more of.  For example, Bacteroides can be considered the good guys and Firmicutes the bad guys.  In both animals and humans, a higher ratio of Firmicutes can be found in the more obese of the species.  It has even been discovered that these evil doers will extract more calories from your food and pass it on to you.  Some studies say that they can generate up to 400 more calories per day for our body than other types of bacteria.  That’s the equivalent of one really strenuous workout or two candy bars.  I am also oversimplifying things because many OTHER types of bacteria are different in thin vs. obese people and animals, but this just gives you an idea.  


Another interesting fact is that larger people and thinner people tend to live in clusters.  Have you ever noticed that?  Some families tend to be larger while others are thinner.  This is not just about their lifestyles and what they are eating.  Is is also because they are sharing…..POOP.  I know that we are all try to wash our hands after using the bathroom, but inevitably we are probably not as sanitary at home as we are in a public restroom.  Also, homes involve a lot of sexual activity which is another way that we share our bacteria.  It has been postulated that skinny people could share their bacteria with their larger family members and vice versa, resulting in a sharing of bacteria as well as similar body size.  This also explains why babies who are born by C-section may have a higher rate of obesity when they grow up….they did not get mama’s good bacteria as much as they would have in a vaginal birth.  It also may explain why people in different countries are smaller, despite eating what would appear to us to be “unhealthy”  (think about France). We have also found that transplanting poop from a thin human to a larger human results in improved glucose control, an increase in energy expenditure, and a reduction in fat.  

If that isn’t enough, these little bacteria have an effect on our brains and behavior too!  Some studies show that ingesting certain types of bacteria can effect how your brain responds to certain emotional situations.  Think about how you devour more sugary foods when you are stressed.  Maybe it isn’t you….its your bacteria!  The types of bugs you possess have also been shown to alter our food preferences.  If we have certain kinds of bacteria we prefer high-fat or sugary food.  

The composition of bacteria is not just inherited or acquired from your environment.  We have found other ways of altering the composition of the microbiome.  One of the most effective treatments that we have for obesity is bariatric surgery.  However, we initially thought that rearranging the stomach and making it smaller was what accounted for the weight loss.  However, we are now finding that these surgeries may actually change the composition of the microbiome, which may be one reason why it is so effective.  

So should you undergo your own home fecal transplant with a skinny person?  No….that’s disgusting!   Should you take probiotics?  Well, it is not that simple.  Studies have not been that promising because the microbiome is a complicated place.  It does not appear that popping a pill every morning can cause the changes in our microbiome that we would like.  This is partly because the bacteria have a hard time surviving all the way to the colon, and partly because they cannot survive when they do arrive because they are not suited for that particular host’s environment.  However, what DOES appear to work is to create an environment that encourages the growth of the good bacteria and discourages the growth of the bad bacteria.  Part of the reason why our bodies have been growing larger over the past several decades is because the composition of our food has changed so much and it is changing the composition of our bacteria.  I don’t have proof but I am willing to guess that Firmicutes REALLY grow well if you feed them Big Macs and don’t eat vegetables.  If all of this is making you feel discouraged, I have hope for you.  Some substances are shown to increase the diversity of the bacteria which produces a pattern similar to that which is seen in thinner people. These are called prebiotics (or bacteria food).  I go over the different types of “bacteria food” that you should be ingesting and the types of food that you should be eating to optimize your ratio of good to bad bacteria in my online course.  For more information, head on over to From Diet Drama to Magnetic Mama Online Class.  If you are concerned that your metabolism might be slow after years of yo-yo dieting, download my free guide to resetting your metabolism:  Reset Your Sluggish Metabolism.  If you are one of my physician readers, and you want THE EVIDENCE, you can read it here: Gut Microbiome and Obesity: A Plausible Explanation for Obesity (Sanmiguel, 2015)



This information is for educational and informational purposes only and solely as a self-help tool for your own use. I am not providing medical, psychological, or nutrition therapy advice. You should not use this information to diagnose or treat any health problems or illnesses without consulting your own medical practitioner. Always seek the advice of your own medical practitioner and/or mental health provider about your specific health situation. For my full Disclaimer, please go to

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