Since the past few years, the popularity of probiotics has grown so much that the types of foods claiming to contain probiotics have expanded to now include cereals, cookies, fruit juices, granola bars, and even candy. In fact, the global probiotic market was valued at around 40 billion dollars in 2017 and is projected to be worth over 65 billion dollars by 2024 (1). With the demand for probiotics increasing, it is important to understand how effective probiotics are in improving gastrointestinal health.
It is estimated that the number of bacterial cells in the human intestine is more than ten times the number of cells comprising the human body (2). Since some of these bacteria are beneficial to health while others are harmful, it is thought that an imbalance of bacterial microflora in the gastrointestinal tract may contribute to the pathophysiology of several GI disorders. Thus, the belief in the beneficial effects of probiotics is built on the fact that a healthy microflora can protect against infections and a disturbance of the microflora can increase susceptibility to infections.
One way in which the microflora in the gut may be disturbed is through the use of antibiotics. While antibiotics are important for treating bacterial infections, they can alter the composition of the gut microbiome. These changes are not necessarily harmful; however, one common side effect of taking antibiotics is diarrhea, which occurs in around 10 to 20 percent of cases (3). In one study evaluating 388 patients who were receiving certain antibiotics while simultaneously taking either a placebo or probiotic, the results revealed that the incidence of diarrhea in patients receiving the placebo was 17.5 percent, whereas the incidence of diarrhea for patients receiving the probiotic was only 4.5 percent (4). Many other studies support this conclusion that probiotics reduce the risk of developing antibiotic-associated diarrhea.
Antibiotic-associated diarrhea poses problems to vulnerable populations. The proliferation of an intestinal pathogen, Clostridium difficile, causes a more severe form of antibiotic associated diarrhea. C. difficile infections can have serious consequences for the elderly or debilitated and standard treatment is generally difficult and expensive (5). Probiotics are seen as an attractive alternative that has the potential to restore intestinal homeostasis. A meta-analysis of 20 randomized controlled trials with 3,818 adults and children reported a significantly decreased risk of C. difficile infections among patients randomly assigned to probiotics compared to a placebo (6). While C. difficile infections have not consistently been shown to be prevented by probiotic use, in practice, many clinicians still tend to recommend probiotics during or after antibiotic treatment.
One common gastrointestinal disorder known as irritable bowel syndrome (IBS) is estimated to affect around 11 percent of the world population (7). People with this disorder generally experience a variety of symptoms including abdominal pain, cramping, bloating, gas, diarrhea and constipation which can be hard to control. While the precise cause of IBS is unknown, it is thought that probiotics may help relieve the overall symptoms associated with this disorder. Irritable bowel syndrome is not life threatening and will not lead to other serious diseases, but it does reduce the quality of life for patients who suffer from it and affect their ability to participate in daily activities. In a clinical trial designed to confirm the efficacy of a specific probiotic, it was found that the probiotic was associated with a significant improvement in symptoms such as abdominal pain, discomfort, bloating, straining, passage of gas and bowel habit satisfaction (8). The trial involved 362 women with IBS and used the probiotic Bifidobacterium infantis 35624 which has shown to be effective in relieving many of the symptoms of IBS (8). The results of this study are promising and encourage future clinical trials focusing on other strains of bacteria to use as probiotics.
Similarly to IBS, lactose intolerance is also extremely prevalent in society. Lactose intolerance is caused by a deficiency of the enzyme lactase which breaks down the sugar lactose, commonly found in dairy products. As a result, people with lactose intolerance generally experience gas, diarrhea, and bloating after consuming dairy products. Recent research has suggested that specific probiotic strains may improve lactose digestion and alleviate symptoms in lactose intolerant individuals. One study that used a probiotic containing two different strains of bacteria found that probiotic intake significantly lowered breath hydrogen concentration, a measure used to indicate the degree of lactose intolerance, and reduced the total score of symptoms (9). There was a significant decrease in bowel movement score and abdominal pain score. Of the 27 patients, the 19 who returned after three months of the probiotic discontinuation for a follow-up test revealed symptom scores and breath hydrogen concentrations similar to the values observed during probiotic supplementation (9). These results indicate that the improvement in lactose digestion and symptoms persisted even after probiotic discontinuation, possibly due to the probiotic bacteria remaining in the gut. Despite these results, research in this specific area is still relatively new and limited, and more evidence is needed to sufficiently determine which probiotics can be considered as a therapeutic alternative for treating lactose intolerance.
While there is considerable potential for the benefits of probiotics over several clinical conditions, there are still major challenges that need to be addressed. For one, questions regarding the most optimal dose for each bacterial strain remain and the mechanisms by which probiotics provide their health benefits are still not understood. In addition to this, studies done on probiotics usually involve a specific bacterial strain and dose; however, when purchasing probiotics from a store, we often do not know what we are getting. The efficacy of probiotics is dependent on a multitude of factors and probiotics should not be considered as the latest “magic pill” for improving one’s health. At best, probiotics provide the greatest benefit for those with certain gastrointestinal disorders, and since each individual’s gut microbiome is different, what works for one person might not work for another person. When choosing a probiotic, it is important to consider the desired health effect, the type of bacteria and overall what works best for you while continuing to maintain healthy dietary and lifestyle habits.
Edited by: Frank Lin
Illustrated by: Angela Chen