Probiotics and chronic disease: a case for consuming (certain) bacteria

Emerging research links a healthy gut with improved prevention and treatment of bowel and metabolic disorders

Emerging research links a healthy gut with improved prevention and treatment of bowel and metabolic disorders

Merritt Drewery          

Probiotics and gut health are at the forefront of current health and nutrition recommendations. In this entry, I define each and provide a background outlining the role of probiotics in promoting gut health and, in turn, preventing and treating bowel and metabolic disorders. Attention is given to the Western diet as this common American dietary pattern disrupts the balance in good to bad gut bacteria. Furthermore, the importance of consuming fermented foods containing beneficial bacteria (yogurt, kombucha) is emphasized and tips for selecting a daily probiotic supplement are provided.


What are probiotics?

            Probiotics are living bacteria that contribute to the balance in gut (intestinal) bacteria and can improve the health of their host (humans) [1]. The term “probiotics” was coined in 1965 and translates to “for life” in Greek. Health benefits of probiotics have been realized for more than a century. In 1908, a Russian Nobel Prize winner discovered that Bulgarian peasants who consumed yogurt (a probiotic-rich food) had reduced amounts of toxin-producing gut bacteria and hypothesized that this was directly related to increased lifespan [2]. 


What is gut health?

            Historically, it was thought that the womb environment was sterile and, as such, the fetal gut was void of bacteria. However, in recent years, low concentrations of bacteria have been detected in the amniotic fluid, placenta, and fetal gut, supporting the idea that the gut bacterial population (also called “gut microbiota”) may be established before birth [3]. At birth, the newborn’s gut is further colonized with bacteria from their mother and the environment [4-6]. Newborns born vaginally have different gut bacteria than those born by caesarean section (c-section) [7]. These differences persist at least until the infant is 2 years old [8] and have recently sparked research in determining which birth type (vaginal or c-section) is associated with greater health benefits for the infant.

            Adult humans have complex “ecosystems” of gut bacteria, encompassing approximately 100 trillion bacteria from an estimated 1000 different bacterial species [9]. Disrupting the ratio of good to bad gut bacteria contributes to development of chronic diseases. These diseases include, but are not limited to, bowel disorders, metabolic disorders, autoimmune disorders, rheumatoid arthritis, and asthmatic/allergic reactions. In this discussion, we will focus on the role of a healthy gut in treating and preventing bowel- and metabolic-related chronic diseases.

Factors contributing to an imbalance between good and bad gut bacteria include obesity [10,11], ageing [12], and the Western diet [13-15]. Yes –  unfortunately, as you age, your gut bacteria gradually shift from a disease-preventing to a disease-promoting population. Weight gain and the onset of obesity are also accompanied by a shift away from beneficial gut bacteria.

Of particular interest is the role of the Western diet in disrupting a healthy gut bacterial balance. Americans are avid consumers of the aptly named Western diet, which is characterized by high intakes of red and processed meat, butter, salt, sugar-sweetened beverages, and refined grain products (i.e., white bread, white rice). These foods are consumed at the expense of fruits, vegetables, poultry, seafood, and whole grain products (i.e., whole wheat bread, brown rice). The Western diet contributes to obesity and type 2 diabetes mellitus from a sheer caloric and energy intake standpoint [16]. However, as discussed above, weight gain and obesity are accompanied by a disruption in the ratio of good to bad gut bacteria, further perpetuating symptoms of this disease state.


Probiotics and bowel-related disorders: recent research

 Inflammatory Bowel Disease

             Ulcerative colitis and Crohn’s disease are characterized by constant gut (intestinal) inflammation. The gut bacterial population is believed to play a significant role in these diseases; it has been shown that ulcerative colitis and Crohn’s disease patients each have reduced levels of Lactobacillus and/or Bifidobacterium in their tissues or feces [17,18]. These are specific bacterial species that are commonly categorized as “good bacteria”. When a probiotic-rich treatment was consumed by ulcerative colitis patients, the symptoms of the disease remained dormant, or inactive [19]. However, this effect was not persistent as, when probiotic treatment ceased, disease symptoms returned [19]. This suggests continual probiotic intake may be necessary to be an effective treatment for ulcerative colitis. The observation of symptom dormancy with probiotic treatment has been replicated by different researchers; however, each provided different bacterial species and at different amounts [20,21]. The most effective bacterial species and amount to prevent and treat inflammatory bowel disease has not yet been defined.    

Irritable Bowel Syndrome

            Patients with irritable bowel syndrome are afflicted by chronic abdominal pain, bloating, gas, and diarrhea. Several clinical studies show probiotic treatment alleviates those above listed symptoms in irritable bowel syndrome patients [22-24]. Furthermore, long-term intervention (1 year) with probiotics improved overall gastrointestinal function [25]. Unfortunately, irritable bowel disease is a heterogenous disorder, meaning those affected by it have different symptoms at varying levels of severity. This complicates the prescription of probiotics to prevent and treat irritable bowel syndrome as, again, the optimal bacterial species and amount has not been defined and likely varies depending on the patient’s symptoms.       

Chronic Diarrhea

            Despite the range of health benefits probiotics confer, probiotic intake is often primarily (and singularly) associated with improved regularity and consistency of bowel movements. Indeed, the use of probiotics in preventing and treating diarrhea is well studied, including in chronic, acute infectious, and antibiotic-associated diarrheal diseases. Here, we focus on chronic diarrhea. Research data reveal that specific bacterial species, together with antibiotics, are effective in treating chronic diarrhea [26,27]. Specifically, Lactobacillus and Bifidobacteria have each been found to support gut function to improve diarrhea as well as constipation [28]. The improvement in diarrheal episodes with probiotic intake has been documented in adults [26,27] and infants [29-31].


Probiotics and metabolic-related disorders: recent research


            Research in animals and humans show that probiotic supplementation effectively reduces body weight and body mass index, a measurement commonly used to assess body composition (normal, overweight, obese) based on an individual’s height and weight [32-34]. As mentioned in the “What is gut health?” section, obesity itself contributes to an imbalance in the ratio of good to bad gut bacteria. Indeed, obese mice and humans have altered gut bacterial populations as compared to their normal weight (lean) counterparts [10,11]. Those bacterial species that are present at greater concentrations in obesity have a greater ability to derive energy from foods consumed, thereby contributing to obesity [35].

The interaction between probiotics and obesity is not just treatment-based; probiotics are implicated in preventing the development of obesity. Probiotic supplements consumed by pregnant women from mid-pregnancy until their baby turned 6 months old reduced their (maternal) weight gain. Furthermore, their offspring had lesser weight gain than offspring from mothers who did not consume a probiotic supplement from birth to 10 years of age [36]. This is an example of “developmental programming”, or how a pregnant woman’s actions during pregnancy affects her offspring’s development and predisposition to chronic diseases, and underlines the importance of probiotics in preventing the development of obesity across the lifespan.  

            Non- alcoholic fatty liver disease is characterized by an inflamed liver associated with a high-fat diet and obesity; alcohol consumption does not factor into this disease. Again, studies in animals and humans support a role for probiotics in reducing the symptoms and severity of this metabolic-related disease [37,38]

Type 2 diabetes mellitus

            Research in animals and humans support a role for specific bacterial species, Lactobacillus and Bifidobacteria, in improving insulin resistance and reducing blood sugar concentrations [39,40]. Patients with type 2 diabetes mellitus who consumed yogurt, a probiotic rich food, had significant improvements in blood concentrations of substances which reflect severity of insulin resistance, including fasting glucose and hemoglobin A1c (a measure of long-term blood sugar control) [41]. In fact, at-risk adults who consume 1 serving (4.5 oz) of yogurt per day have a 40% reduction in the risk of developing type 2 diabetes mellitus than those who consume low amounts of yogurt (less than 0.5 oz per day) [42]. “At-risk” adults are defined as those who are more likely to develop type 2 diabetes mellitus based on current lifestyle and/or metabolic factors (i.e., they are smokers, obese, or have high blood pressure).


Probiotics in the diet

         Fermented foods are rich in beneficial bacteria. These foods include yogurt, kombucha (fermented tea), sauerkraut, kefir, and miso. Kombucha is gaining traction as a hot “foodie” item. Kombucha breweries are opening at a rate which mimics that of the early 2010s craft beer scene and most major grocery stores now carry a few kombucha options. Home-brewing kombucha is an economical, fun, and addicting option. For those curious (and brave!) souls, I suggest researching brewing methods online, obtaining a SCOBY, and getting started… it’s easier than you think. Links for further reading and “how-to” are at the end of this entry.

You can also up your intake of beneficial bacteria by taking a daily probiotic supplement. In choosing the supplement, you should take care in ensuring it contains multiple species of bacteria (at least 10) and at high concentrations. It is worth restating that the “optimal” blend and amount of bacterial species to prevent and treat chronic diseases has not been defined. However, the benefits of the bacterial species Lactobacillus and Bifidobacteria were mentioned several times throughout this entry and, as such, should be included in your daily probiotic supplement.

Probiotics are measured in colony forming units, denoted on the bottle as “CFU”. In researching a supplement to treat my mother’s rheumatoid arthritis (watch out for a blog on this in the future!), I commonly saw 3 – 50 billion CFUs as recommended potencies. Ultimately, I chose a probiotic with 20 billion CFUs. Ensure the CFUs claimed on the front label are for one serving size (or you are okay with taking 2 capsules per day). Commonly, labels will claim “20 billion CFUs per serving” but, upon inspecting the Supplemental Facts label, you realize one serving equates to 2 capsules and the product is not as potent (or economical) as originally perceived.



            Emerging research suggests probiotic consumption may have efficacy in preventing and treating bowel and metabolic disorders. Unfortunately, optimal species and amounts have not yet been established. The role of the Western diet and obesity in shifting the gut bacterial population to a disease-promoting state should be given consideration and prompt dietary alterations. Specifically, increased fruit, vegetable, and fermented food consumption would promote beneficial gut bacterial growth. As stated, probiotics and a healthy gut are implicated in various chronic diseases, not just those covered in this entry. As such, probiotics are a part of a healthy, preventative lifestyle and recommendations given here are not exclusive to those afflicted by adverse bowel or metabolic conditions.

Author Bio
Merritt Drewery is a native of Baytown, Texas. She holds a Bachelors of Science and Masters of Science in Animal Science, with a focus in Ruminant Nutrition, from Texas A&M University. Merritt recently received her PhD in Molecular and Clinical Nutrition from Louisiana State University. Her research interests include the role of perinatal nutrition in optimizing fetal and infant development, especially in infants born to women with adverse metabolic conditions. In her free time, she is probably playing with her very scruffy, disobedient dog or showing pictures of her nephews to anybody who will feign interest.


Further kombucha reading:;;



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