BiotiQuest® Gut Health & Probiotics Blog with Martha Carlin

Gut Health 101: Do Bacteria Feed on Sugar?

Martha Carlin | Jan 04, 2024 |

Gut bacteria play a vital role in sustaining human health. With over a thousand different bacterial species making their home in the human gut, the composition of your diet - complex carbohydrates (fiber) versus simple sugars (fructose and glucose) - plays a vital role in maintaining health.

Different microbial species need different foods to thrive and increase their population. Typically, diets rich in complex carbohydrates such as plant-based fibers promote a diverse microbiome, which has an overall protective effect on your health. Whereas the Western diet rich in simple sugars and trans fatty acids promotes gut dysbiosis - an imbalance in the gut microbiome where an overabundance of pathogenic or bad bacteria overcomes that of the beneficial or good bacteria - resulting in ill health by triggering a cascade of metabolic events like inflammation, insulin resistance, and diabetes. 

The composition of the gut microbiota impacts health by altering how well you sleep, process blood sugar and cholesterol, absorb, and synthesize nutrients, or maintain the strength of the gut barrier and in turn your immune system.

To understand how sugar impacts your health, let's dive into how different types of sweeteners interact with the gut microbiome and impact the gut barrier, and how a cascade of metabolic events might result in metabolic disorders such as diabetes and NAFLD.

Is all sugar equal?

Not all sweeteners are created equal or have the same impact on the human body. Different types of added sugar make their way into the food you eat and interact with the gut microbiota. The most commonly used sweeteners found in food are:

  • Nutritive (glucose, sucrose, and fructose)
  • Polyols or sugar alcohols (xylitol, sorbitol, lactitol, etc)
  • Non-nutritive (advantame, saccharin, sucralose, etc)

Different sweeteners interact differently with your digestive system and gut bacteria. For instance, the sugar you get from eating whole fruit is not the same as table sugar. Eating whole fruits adds not only naturally occurring fructose and polyols into your diet but also fiber and micronutrients, which are essential for a healthy gut microbiome and body.

Consuming highly processed foods leads to an overconsumption of a range of dietary sweeteners without the balancing effect of dietary fiber, which over time might trigger gut dysbiosis and metabolic disease.

As awareness about the ill effects of sugar consumption is rising, so is the demand and use of sugar alternatives. But sugar alternatives come with their own set of pros and cons, understanding the health effects of alternatives such as artificial sweeteners and sugar alcohols on the gut microbiome is paramount before adding them to your daily diet.

For instance, a study observed that consumption of acesulfame k (an artificial sweetener) depleted the abundance of Akkermansia muciniphila, a strain that plays an important role in maintaining the structural integrity of the gut barrier thus preventing the leakage of toxins such as LPS into the bloodstream.

Does an increase in dietary sugar lead to an increase in bad bacteria?

Several studies associate a high-sugar diet (HSD) with the development of gastrointestinal, cardiovascular, and neurological diseases such as hypertension, insulin resistance, and cognitive decline, etc. To understand how HSD might trigger disease in the body, let's understand what a balanced gut or gut homeostasis might look like.


What is human gut homeostasis?

The human gut and its microbial residents have a complex give-and-take relationship. Gut homeostasis is a state where a diverse microbial composition favors and maintains host health, and has a protective effect on the gut by producing metabolites that counteract stress, inflammation, and pathogenic invaders. 

Generally, bacterial families known as Firmicutes make up for more than 50% of your gut microbes, followed by Bacteroidetes at about 25%, and the rest is followed by Proteobacteria and Actinobacteria, respectively.

Gut microbiomes may vary across geographical regions based on traditional diets and are considered healthy as long as they favor host health. Even within bacterial families, some species such as bifidobacterium and lactobacilli are considered good bacteria, while the increased abundance of species such as Escherichia coli and streptococcus mutans is considered bad.  

What happens when gut homeostasis gets disrupted?

A diverse gut microbiome is a healthy gut microbiome. Your gut microbiota varies on a daily basis, depending on what you ate in the last few days, but largely stays the same as we tend to eat similar foods on a regular basis.

Diets rich in sugar promote the growth of bacterial populations that might produce by-products that have a negative impact on the gut as well as displace beneficial bacteria and their protective effect leading to a disrupted gut homeostasis.

A large part of the immune system resides in the gut and works to protect you from bacterial pathogens. Compromised intestinal permeability allows pathogenic bacteria and their toxic metabolites to enter the bloodstream which triggers the immune system to release pro-inflammatory molecules in order to protect you from these foreign invaders.

In the short term, inflammation is a protective measure and is essential in maintaining optimal health, but long term low-grade inflammation might lead to a host of metabolic events which can translate to diabetes and other metabolic disorders.

High sugar diet reduces gut diversity


Glucose and fructose are absorbed in the small intestine but too much sugar leads to an overflow into the large intestine along with polyols and artificial sweeteners.

The availability of excess sugar in the large intestine is associated with the accelerated growth of pathogenic bacterial species such as Clostridia and a decrease in beneficial bacteria such as Lactobacillus spp.

HSD has been linked with a decrease in gut bacteria diversity, a decrease in the abundance of Bacteroides as well as an increase in Proteobacteria. These changes in the gut microbial composition are similar to changes that have been observed in individuals with metabolic disorders such as inflammatory bowel disease, etc. 

Too much sugar has also been linked with an altered Firmicutes to Bacteroidetes ratio. A healthy Firmicutes to Bacteroidetes ratio is considered essential to gut homeostasis and an imbalance in favor of Firmicutes is often associated with obesity and an imbalance in favor of Bacteroidetes is associated with IBD.

Does eating sugar displace beneficial bacteria?

Gut bacteria compete for resources and have a preference for foods that help them thrive. When you eat a diet rich in complex carbohydrates, it supports the growth of beneficial bacteria that are essential to the maintenance of your gut such as short-chain fatty acids (SCFAs) producing bacteria - SCFAs are the primary energy source for intestinal cells and help maintain the integrity of the gut wall - whereas consuming simple sugars does not support the growth of beneficial bacteria.

For example - In a mice study, researchers found that a high sugar intake and high-fat diet could be associated with a decrease in the abundance of segmented filamentous bacteria (SFB). The increased sugar diet led to the growth of Faecalibaculum rodentium which outcompeted SFB out of the gut.


Researchers found a relationship between the presence of SFB and the development of Th 17 cells in the gut since the decrease and loss of segmented filamentous bacteria were found to be correlated with the depletion of intestinal Th17 cells. 

Th17 cells are associated with both protective effects such as regulating fat absorption as well as a proinflammatory response, which can be associated with several autoimmune diseases such as MS and SLE.

The development and the type of impact Th 17 cells exert on the gut are dependent on certain bacterial populations, which trigger its development, and the overall composition of the gut microbiome. 

In the case of mice that were fed a high-sugar diet and lacked SFB and thus Th 17 cells were found to be vulnerable to weight gain, glucose intolerance, and insulin resistance. Similarly, mice that were fed a high-fat diet but were not colonized by SFB gained weight and developed diabetes.

On the other hand, mice that had been colonized with SFB and thus had Th 17 cells were fed only a high-fat diet and continued to be protected against weight gain, glucose intolerance, and insulin resistance.

In a separate human personalized diet-microbiome dataset, it was found that increased sugar intake was associated with a decrease in the abundance of Th17 cell-inducing filamentous bacteria in humans.

Researchers concluded that probiotic supplementation of Th17 cell-inducing bacterial strains could help improve diet-induced obesity (DIO) and metabolic syndrome by regulating intestinal T Cell homeostasis.

What is metabolic syndrome (MetS)? Can dietary sugar trigger MetS?

Metabolic syndrome is a collection of risk factors that might eventually culminate into cardiovascular events such as heart disease and stroke and metabolic diseases such as diabetes. 

Risk factors that come under the umbrella of metabolic syndrome include obesity, high cholesterol, high blood pressure, high sugar, chronic inflammation, etc.

What leads to metabolic syndrome?

Obesity is largely influenced by diet. Western-style diet, which includes a high intake of sugar and fat, initiates a cascade of events that ultimately result in obesity and obesity-associated metabolic syndrome and type 2 diabetes.

The thousands of microbial species present in the gut produce molecules that can either have a positive or negative effect on our overall health and on whether an individual starts to develop metabolic syndrome-associated risk factors.

On the one hand, microbial molecules can act as nutrients and energy sources for intestinal cells and also have anti-inflammatory and antioxidant functions. On the other hand, they can include toxins such as LPS, etc. 

In mouse models, a diet high in fat and sugar is associated with an increase in the number of Firmicutes and Proteobacteria and a decreased abundance in Bacteroidetes and Verrucomicrobia.

In another study in mice, dysbiosis and a decrease in SCFA-producing bacteria were linked with compromised barrier function and increased intestinal inflammation.

A high glucose and a high fructose diet in mice was found to reduce gut diversity and increase lipid accumulation. Other studies link the lack of gut microbial diversity with hypertension and the lack of SCFA-producing microbes. 

NAFLD or non-alcoholic fatty liver disease is another risk factor included in metabolic syndrome. Some studies associate chronic low-grade inflammation due to leaky gut syndrome with the induction of NAFLD.

Gut microbiome and the immune system


The gut microbiome plays a vital role in shaping the intestinal immune system by triggering the development of innate and adaptive immune systems. For instance - the development of Th 17 cells is dependent on the presence of segmented filamentous bacteria (SFB) in the gut.  

Researchers associate several metabolic diseases with low-grade chronic inflammation which results due to gut dysbiosis and a compromised gut barrier. Gut barrier integrity is an important denominator when it comes to the development of metabolic conditions. 

A healthy gut microbiome of beneficial microbes encourages the production of mucus, which strengthens the intestinal gut lining, while a dysbiotic gut leads to an eroded gut lining, letting gut bacterial cells pass through the gut wall and into the bloodstream. This leads to immune system led inflammation which is correlated with the development of metabolic syndrome.

Prebiotics and Probiotics for optimal health

While consuming sugar disrupts your microbiome, adding whole fruit and vegetables, which are full of complex carbohydrates aka prebiotics, are needed for the growth and sustenance of beneficial bacteria, meet your daily fiber requirement, and improve your health. 

You can also give your gut health that desired boost with our probiotic formula Ideal Immunity, rich in beneficial bacterial strains such as B. bifidum and L. plantarum, or add fermented foods such as yogurt, which you can make at home without any added sugar, using our Sugar Shift® Starter Culture for that additional punch of probiotics to enhance your diet.

With gratitude,

Martha Carlin photo Martha Carlin, is a “Citizen Scientist”, systems thinker, wife of Parkinson’s warrior, John Carlin, and founder of The BioCollective , a microbiome company expanding the reach of science and BiotiQuest, the first of it’s kind probiotic line. Since John’s diagnosis in 2002, Martha began learning the science of agriculture, nutrition, environment, infectious disease, Parkinson’s pathology and much more. In 2014, when the first research was published showing a connection between the gut bacteria and the two phenotypes of Parkinson’s, Martha quit her former career as a business turnaround expert and founded The BioCollective to accelerate the discovery of the impact of gut health on all human disease. Martha was a speaker at the White House 2016 Microbiome Initiative launch, challenging the scientific community to “think in a broader context”. Her systems thinking background and experience has led to collaborations across the scientific spectrum from neuroscience to engineering to infectious disease. She is a respected out of the box problem solver in the microbiome field and brings a unique perspective to helping others understand the connections from the soil to the food to our guts and our brains.

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