Lifestyle Medicine & Wellness Blog

Our Gut Microbiome Affects Weight Gain!

In my practice I work with patients to optimize gut health as a means of optimizing their health.  Patients come to me with a plethora of symptoms such as brain fog, digestive issues, skin rashes such as eczema, low energy, muscle pain and fatigue, weight gain, cardiovascular issues like increased cholesterol and atherosclerosis, food allergies and sensitivities, immune system issues and autoimmune disease and more.  Most everything begins in the gut whether they realize it or not.

It is becoming increasingly clear that this is true – “If you’re gut isn’t healthy, you are not healthy!”


Did you know there is a dynamic relationship between the bacteria in the gut and obesity?

There are many plant carbohydrates that we cannot digest fully, but the bacteria in our gut can break them down and convert them into something called SCFA, short chain fatty acids.  (For those who want more specific detail, three of the important SCFA are butyrate, acetate and proprionate.)  SCFA are critical for the health of our intestinal tract!

Our cells in the colon then use butyrate as their chief energy source, while the acetate and proprionate are needed for the liver to make fatty acids and glucose.  The amount and types of SCFA in our gut microbiome are important markers when we compare obese vs. normal weight individuals’ gut composition, because there are differences in the types and amount of SCFA in lean individuals vs. in the obese.

An interesting study compared mice raised in a normal environment (exposed to bacteria and who had normal gut microbiota) to "germ-free" mice who had no bacteria in their gut.  The “normal” mice that had bacteria in their guts “had 40% higher body fat content and 47% higher gonadal fat content than germ-free mice” - without consuming any more food than the germ-free mice.

So we can ask, does the amount and type of gut bacteria affect our tendency to accumulate body fat and increase total weight?   And we can wonder given this study, if modifying our gut microbiota may be a means to more efficient weight loss.

But there’s more.  Researchers then implanted some of the gut bacteria from the normal mice into the germ-free mice and within 2 weeks, body fat increased by 60% - even without an increase in food consumption!

In genetics, we talk about the GENOTYPE (your genetic make-up) and your PHENOTYPE (or phenotypic expression, which is how your genes are expressed, whether in health or disease).   Gut microbiota composition, then, affects our genes and how our genes are expressed.  In this example, the affect is an increase in the amount of energy utilized from the food consumed, and then, additionally,  an increase in the amount of fat stored ultimately leading to obesity.

Part of what makes weight loss so challenging is that it is a multi-factorial problem.   One area recently being studied is the affect of antibiotics on our microbiome and our health over time.  The rise in antibiotic use over the last several decades has drastically modified our gut bacteria balance.  There seems to be a linear increase in obesity that matches the increase in the use of antibiotics.  Remember antibiotics kill off the bad bugs, but at the same time, kill off the good bugs as well.  How does that affect weight gain (fat deposition and obesity)? 

Well, studies in mice show that mice who were exposed to penicillin in utero and whose mothers continued on penicillin prior to weaning the babies showed a number of physiologic imbalances, including marked  changes in body composition as an adult.  Total weight and total fat percentage were higher; the genes in the liver responsible for producing fat were up-regulated to produce more fat; and bone mineral content (bone density) was altered as well as bone surface area.  Sadly, it seems that exposure to antibiotics early in life can have detrimental affects on body composition that lasts a lifetime.


Ok, so this is all well and good and interesting in mice, but what about in us humans??

Well, if we look at bacteria diversity (the numbers and different varieties of bacteria in the gut), we see that having a low diversity negatively affects our physiology.  Low diversity translates to much higher levels of obesity (overall body fat) and imbalance in lipids (higher cholesterol); poor blood sugar control; a greater level of low-grade inflammation (which is the precursor to all chronic disease) and an increase in  the tendency towards obesity and chronic disease. 

The obese subjects not only had less diversity of bacteria, but they also had higher levels of a bad bacteria species (Firmicutes), and almost 90% lower levels of the important good bacteria (Bacteroidetes) than the lean counterparts.  Additionally, the obese that lost weight on a low carbohydrate or low-fat diet were able to  increase the Bacteriodetes and decreased the Firmicutes some, but never to the same levels of the lean participants.

So what comes first, the chicken or the egg?  That is, do we get an imbalance in gut bacteria and then gain weight, or does the excess weight trigger inflammation and damage the microbiota.  I would say both are probably true - at least we know dysbiosis results in inflammation and a cascade of health issues.  But if we know that keeping the gut balance healthy can help prevent excess fat accumulation, then we may have some new tools in our fight against obesity in our country. 

How early in life might this be important?   Well, infants at ages 6 and 12 months with more of the bad bacteria in their gut microbiota had a greater risk of being obese at age 7 than those with more balanced bacteria in their gut.  Does this prove that the bacteria balance comes before the weight gain and is a trigger to obesity?  It seems likely it may, at least, play a significant role.

What does all this mean for us?  Wow! We can see that increasing our gut bacteria diversity is very important to our overall health! In the last several decades we have seen an explosion in overweight and obesity in nearly all 50 states.  The cause is no doubt multi-factorial (more on that in another blog), but the rise in antibiotics use seems to be linear with the rise in obesity.  The effect on the health of our nation is catastrophic.  Obesity is associated with many chronic diseases including diabetes, cardiovascular health and cancer.  As a matter of fact, nearly every chronic disease is associated with inflammation, and nearly all inflammation comes from the gut. 

We can work to optimize our health now by working to balance our body systems and strengthen our gut health with the right diet, exercise, nutritional therapies and lifestyle strategies.  I can help you with a personalized medicine approach to getting you back into balance and a customized wellness plan tailored to your needs and situation.

Email me at for your free initial phone consult to see what I can do to help you get well today!

Watch for our new blog series TBT – Throw Back Tuesday – where I’ll review patient case studies so you can follow their journeys to wellness!!


 Nutr Today. 2016 ; 51(4): 167–174.

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