Sugar: Not so Sweet for the Gut Microbiome

Many people enjoy sugary foods daily due to their sweet taste and delicious appearance. Let’s face it, donuts, cookies, and candy bars just sound better than broccoli and apples! While eating sweet treats periodically isn’t likely to cause major health concerns, eating too much sugar too often can be a major problem for health and wellbeing.

Unfortunately, most lovers of sugary foods eat them without understanding the significant amount of problems they can cause. Excessive sugar intake can lead to all sorts of health issues including liver toxicity and other chronic diseases, and it also can cause the brain to form addictions, much like those of tobacco and alcohol. On top of all that, it can also have a huge impact on the gut microbiome.

What is the gut microbiome, and why is it important?

The gut microbiome consists of trillions of organisms that not only influence the body’s susceptibility to infection and disease, but also allow it to function properly. There are certain types of bacteria that live there which prevent inflammation and fend off bad bacteria that could cause different diseases and conditions like Inflammatory Bowel Syndrome (IBS). For the gut microbiome to function properly and keep the body healthy, the varying types of bacteria living there must be balanced so that the bad bacteria does not take over. The good bacteria living in our gut also allow us to properly digest food, absorb nutrients, produce chemicals our brain needs to function, and much more.

This means that any food or other product that has the potential to alter the composition of the gut microbiome also has the potential to make the body more prone to disease, illness, and infection.

How can sugar impact the gut microbiome?

Recent research shows that the gut microbiome is intricately linked to the foods we consume. After all, the bacteria in our digestive tract eat whatever we eat! Unfortunately, sugar is one of the foods that has been shown to reduce the diversity of the gut microbiome. In this study, researchers found that mice fed a high-fat/high-sugar (HF/HSD) diet had significantly less diversity in their gut microbiomes than those fed a low-fat/low-sugar diet (LF/LSD). Their microbiomes also shifted towards more pro-obesity bacteria and less types of bacteria that prevent inflammation and weight gain.

This shift was reflected in their body weight and body fat amounts. HF/HSD mice were significantly heavier than LF/LSD mice, and they also had more body fat.

These results have been found in other studies as well. One study involved mice who were fed high-fructose and high-glucose diets (glucose, fructose, and sucrose are naturally-occurring sugars). Researchers found that both groups of mice experienced huge changes in their gut microbiomes, again in favor of pro-obesity and pro-inflammatory bacteria. This led to an increase in inflammation, and then to increased gut permeability. Increased gut permeability (leaky gut) can lead to many problems including increased inflammation, lipid accumulation, and ultimately obesity. Leaky gut can also cause a variety of brain-based problems such as foggy thinking, memory changes, mood problems, and more.

Yet another study with mice showed that serious problems arose for pregnant mice when they were fed fructose daily. These mice had significantly less diverse gut microbiomes, and multiple species of beneficial bacteria were absent. In addition, birth complications arose including increased insulin response to pregnancy, increased fat mass, and reduced body weight in babies. There was also a reduction in gene expression for gut barrier function, meaning the babies would be more susceptible to pathogenic bacteria or other illnesses. All these changes have the potential to negatively impact growth of the offspring as well as healthy gut development.

Sugar also influences the composition of the gut microbiome in another way. A recent study found that consumption of glucose and fructose prevents the production of a certain protein that is necessary for the colonization of good bacteria in the digestive tract. In essence, the sugar stops the body from producing the protein needed by certain types of bacteria to survive in our gut microbiome, and so those types of bacteria were wiped out and replaced by bad bacteria. This alteration can lead to many health problems including inflammation, disease, and infection.

Studies in humans have shown similar results. Researchers have discovered that obese teenagers with higher fructose intake lack specific types of bacteria in their microbiomes that are very beneficial. These types of bacteria (Eubacterium and Streptococcus) are extremely important for healthy carbohydrate metabolism. Without them people can become overweight and develop insulin and sugar regulation issues, like diabetes.

We are just beginning to understand the many problems that can arise when humans consume sugar on a regular basis. The research done so far shows that there are many reasons to be concerned about high sugar intake and the impact it has on gut

microorganisms. We’ve known for years that sugar causes health problems like obesity, diabetes, liver disease, and more. Now we also know that high sugar intake damages our gut microbiome, and that can have a negative impact on virtually every aspect of our health and functioning. For all these reasons, it’s best to avoid added sugars and reduce overall sugar intake whenever possible. Save the donuts and cupcakes for a once-in-a-while treat, and eat more fruit, veggies, and other whole foods daily. Your whole body, and the good bugs that live within it, will thank you!




Dr. Nicole Beurkens, PhD, CNS

Licensed Psychologist and Board Certified Nutrition Specialist

The world’s leading Holistic Child Psychologist, Dr. Beurkens heads a multidisciplinary evaluation and treatment clinic, is a bestselling author, published researcher, award-winning therapist, and devoted mother of four. In her more than 22-year career, she has supported parents with evidence-based strategies that target the root cause of children’s attention, anxiety, mood, and behavior challenges, empowering them to achieve their highest potential. Dr. Beurkens is a licensed clinical psychologist who holds advanced degrees in psychology, education, and nutrition. 

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