Using Bacteria to Control Your Weight

This is the second in a series about the gut microbiome. Recent research has implicated the microbiome in colitis, IBS, obesity, depression, autism, cancer, Alzheimer’s and diabetes. This article explores the role of the microbiome in weight management. We are familiar with traditional reasons for weight gain: unhealthy diet, sedentary lifestyle, unlucky genes. Recent studies suggest that billions of gut microbes may also play a role. Nurses Announcements Archive


Specializes in Oncology, Home Health, Patient Safety.

To read Part One in this series, go to Trust Your Gut? A Fecal Transplant Could Change Your Life

Sally (not her real name), a 32-year-old-woman, was visiting her physician for a routine follow up appointment after a long battle with a Clostridium difficile infection (CDI). Though she was overjoyed with the results of her Fecal Microbiota Transplant (FMT), she was struggling with a new problem.1 (Read more about FMT in my blog)

Sally stepped off the scales, shook her head and said with a frown, “I don’t understand why I can’t lose weight.” Her weight that day was 170 pounds, which at 5 feet tall, put her BMI at 33. “I’ve never struggled with my weight before. I don’t get it.”

The nurse typed the information into her chart and asked, “How are you feeling? Any diarrhea?”

“No, none – that’s finally over with! I can’t believe it’s been over a year since I was at death’s door.”

The nurse smiled and said, “You’ve come a long way since then, that’s for sure. I’ll tell the doctor about your weight gain and we’ll look at some options.”

Sally’s weight before the FMT was stable at 136 pounds (BMI of 26). Her BMI had always been within normal range. Her weight was also stable during the course of illness. She had no significant medical history and an unremarkable physical examination. Sally’s serum cortisol and thyroid panel were also normal.

After talking to Sally, the physician prescribed a medically supervised liquid protein diet and an exercise program. Sally followed both with dedication; however, over the next few months she continued to gain weight. At a subsequent check-up 36 months post-FMT, despite efforts to diet and exercise, Sally’s weight was 177 pounds (BMI of 34.5). She had also developed constipation and unexplained dyspeptic symptoms.

Sally had received the fecal material that had cured her CDI from her 16-year old daughter Amanda (not her real name). At the time of the FMT, Amanda’s weight was 140 lbs (BMI 26.4), but it increased later to 170 pounds.


What are some possible reasons for Sally’s unintentional, rapid weight gain? Sally’s weight gain can’t be explained by obvious reasons for weight gain: unhealthy diet, sedentary lifestyle, unlucky genes. It is possible that the resolution of the CDI caused an increase in appetite, but why didn’t she lose weight with the prescribed liquid diet? It’s also possible the H. pylori treatment caused some weight gain. There’s evidence for weight gain after treatment -related to restoration of ghrelin levels after eradication of bacteria. The researchers who wrote up Sally’s story suggested that her weight gain was caused by the particular make-up of the bacteria in the stool she received from her obese daughter.1&2


Obesity is known to be a major public health problem affecting more than 1.9 billion adults – this means 39% of adults are considered obese and overweight.2 Obesity is associated with multiple comorbidities including cardiovascular disease, metabolic syndrome and cancer. There is a positive linear relationship between mortality and BMI. As nurses, it’s important to be aware of new research that might help the 160 million American adults suffering from obesity.2


So what’s in our gut that might be making us fat? The human gut is home to more than 1000 species of bacteria. Your gut microbiome is like an identity card – highly specific to each individual. The bacteria living in our gut help us digest high fiber foods the stomach and small intestine can’t handle, aid in production of vitamins B and K, and are a huge part of our immune system – defending us against harmful microorganisms. Recently, researchers have discovered that gut bacteria can alter how we store fat, how we balance glucose, and if we feel hungry or full.3

The gut microbiome is an acquired organ. Babies are born sterile with intestinal colonization beginning after birth. Bacteria come from the mother’s lady parts, feces, skin, breast etc…as well as the environment in which the delivery takes place. Our gut microbiome evolves as we grow and develop. This is one of the reasons why we’re being encouraged to embrace a certain amount of dirt in the lives of our children. The composition of the gut microbiota changes over time and is influenced by diet and overall health. In the U.S. obesity rates correlate with antibiotic use – highest in the South.3


There are two main populations of bacteria in the gut: Firmicutes and Bacteroidetes (90% of the total species). The composition of the bacteria in the gut differs between lean and obese people. The Firmicutes/Bacteroidetes ratio higher in obese and overweight subjects (BMI>25) and in those with type 2 diabetes.

Studies of obese/lean twins showed that the lean twin had a much more diverse microbiome than the obese twin. It was found that lean individuals had a wider variety and greater number of bacteriodetes – these specialize in breaking down bulky plant starches and fibers that the body can use for energy.

Research with genetically identical mice in a germ-free environment showed that mice populated with microbes from obese women grew heavier and had more body fat than those populated with microbes from the lean twins. The obese mice also had a less diverse microbiome.

In addition, it was found that a diet of highly processed foods is linked to a less diverse gut. Mouse chow high in fat and low in fruits, veggies and fiber caused obesity. The link to diet is found in newborns as well. Formula-fed babies and infants delivered by cesarean section have a higher risk for obesity and diabetes than those who are breast fed or delivered lady partslly. 4


So the burning question is “Can poop make you skinny?” In a small study of 15 patients, the BMI decreased an average of 1.5 points after FMT from donors with a normal BMI. This reduction was maintained at 3, 6 and 12 months after procedure. However, in another study with 70 patients, there was a decrease in BMI at first but it didn’t last.5

The answer is, we don’t know yet. Preliminary studies have been inconclusive and at this time there is still no magic pill or FMT that can make you lose weight. However, clinical trials are happening! A search of clinical trials recruiting for obesity treatment with FMT yielded six studies, though you’ll have to travel to participate – they’re in Hong Kong, Finland, Canada. 6


In the next installment of this series, I’ll explore the relationship of the gut micriobiome to mental health. There’s research out there linking the gut microbiome to anxiety, depression and it’s exciting stuff. Read more about FMT HERE

Trust Your Gut? A Fecal Transplant Could Change Your Life


  1. Alang, N. & Kelly, C. R. (2015). Weight gain after fecal microbiota transplantation. Open Forum Infectious Diseases, 2(1). Retrieved from:
  2. The Gut Microbiome Profile in Obesity: A Systematic Review (2018)
  3. Everything you always wanted to know about the gut microbiota…
  4. How gut bacteria help make us fat and thin (2014)
  5. Can a Poop Transplant Change Your Weight? (2017)
  6. Clinical Trials

I find this all fascinating. In fact my Amazon.Smile account donates to “OpenBiome” (when I remember to log in).

I got interested in their work when I feared we might lose my father to the triple whammy of pneumonia contracted while undergoing chemo followed by c.diff. acquired at his less-than-stellar (don’t get me started) rehab home.

My interest has increased in learning about cases like the one mentioned above. As a woman who now struggles with weight but was thin growing up (& whose Mother struggled mightily with weight) I am very interested to know what part gut colonies play! Thanks for some interesting reading! I look forward to the next installment!

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