Mechanisms of action and health benefits of probiotics: a comprehensive review

Abstract

Probiotics, originating at birth, play a crucial role in the development and maintenance of a healthy and disease-free environment within the gut of both humans and animals. These beneficial microorganisms from fermented, processed, and non-dairy foods provide numerous health benefits, such as stress reduction, disease prevention, immune stimulation, gut microbiota control, nutritional supplementation, diarrheal disease relief, vitamin production, weight management, and anticancer activities. With more health problems on the rise and the negative side effects of conventional medication and antibiotics prevailing, natural supplements such as probiotics are a relief. Probiotics, such as Lactobacillus, Bifidobacterium, and Saccharomyces, have been identified as safe and effective candidates for gut health applications. This review addresses the current understanding of the mechanism of action of probiotics, their functions in human health, and their therapeutic potential for various diseases. We emphasize the importance of prioritizing probiotic administration along with conventional medicinal drugs for their wide benefits and fewer side effects. Our findings aim to direct future studies on the modes of action of probiotics against emerging health challenges.

Introduction

In the early days, a relationship between microorganisms and humans was observed. It is a very interesting fact that humans cannot survive without microorganisms. In the human body, the head to toe is covered with microorganisms, which protect the human body. The gut contains complex, stable, and beneficial microorganisms that help in various ways, such as digestion of food, increasing immunity, and providing many necessary enzymes. Microbiota refers to the various groups of microorganisms, such as bacteria, archaea, eukaryotes, and viruses, that are present under specific conditions. Gut microbiota community composition can be changed due to some factors. In this microbial jungle, a variety of microorganisms (fungi, viruses, bacteria, and even parasites) can inhabit it. It was previously mentioned in the literature, 100 trillion microorganisms reside in the intestine, which is 10 times larger than the cells of the human body [1]. Currently, the good bacteria in the gut have been compromised because of the modern lifestyle, introducing many pathogenic bacteria to the gut, which prevents the beneficial role of good bacteria. It is logical to increase the number of beneficial bacteria to maintain good gut health [2]. Many bacteria help cure diseases by having a symbiotic relationship with the host.

These are referred to as probiotics. Probiotics, defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”, Anjana and Tiwari [3] 2022, have been studied for their ability to promote a balanced and diverse gut microbiome, which is essential for maintaining overall health [1]. If a sufficient amount of these bacteria is ingested, they can confer several health benefits, such as those provided by gram-positive bacteria like Lactobacillus and Bifidobacterium [4]. Overconsumption of antibiotics can disturb gut microbiota functionality, thereby killing beneficial microorganisms. Antibiotics usually fail to differentiate between beneficial and harmful microorganisms. The main reasons for antibiotic resistance are improper use of antibiotics, lack of proper knowledge, and misuse of antibiotics [5, 6].

Frequent use of antibiotics also destroys genital tract bacteria and weakens the immune system. This issue has encouraged researchers to find natural alternatives to restore the good bacteria in the body and treat a variety of gastrointestinal infections [7]. The primary source of gut microbiota is the mother, who transfers the gut microbiome vertically during birth. The composition of the gut microbiota depends on the mother’s flora, genetic factors, and medication use. 97% of the gut bacteria are anaerobic, and the majority of strains found are Bacteroidetes (Porphyromonas, Prevotella, and Bacteroides), Firmicutes (Ruminococcus, Clostridium, Lactobacillus, and Eubacteria), and Actinobacteria (Bifidobacterium) [4, 8–10]. Recent studies have shown that probiotics may help improve immune function, protect against pathogenic bacteria, affect the gut-brain axis, and aid in the adsorption of food and nutrients (Figure 1). In addition, probiotics can play a role in the gut, providing beneficial gut bacteria that create a physical barrier to prevent unwanted bacterial ingestion. Therefore, the benefits of probiotics can be addressed as the prevention of diarrhea, irritable bowel syndrome (IBS), ulcerative colitis, and Crohn’s disease. The gut-brain axis is also interconnected, and many studies have suggested that probiotics may help in the management and regulation of mental disorders. A clinical trial with 86 students found that after treatment with probiotics for 28 days, there were improvements in their behavior, such as panic anxiety, neurophysiological anxiety, worries, and mood regulation. In addition, a clinical study reported that probiotic mixed strains of Lactobacillus reuteri NK33 and Bifidobacterium adolescentis NK98 for 8 weeks improved mental health and sleep [11].

To ensure health benefits, a good amount of probiotics in the gut is required with regular food intake. The strains of probiotics should be from human sources and contain a few major features, such as: 1. benefits to the host, 2. survival in the intestine, 3. it is also used as a feed additive to improve the intestinal epithelial cell (IEC) membrane, 4. creation of antibiotic substances against infections, and 5. stabilizes intestinal microflora. The number of probiotics should be large enough to provide a sufficient number of bacteria in the gut [7]. Lactic acid bacteria (LAB) are good sources of probiotics, except for Streptococcus and Enterococcus. In many food products, LAB are widely used without any adverse effects. Probiotics are mostly isolated from the human gut, and it is known that large quantities of probiotic consumption are advised as a functional food; for example, Bifidobacterium can be found 1011 cells/g in the intestine [12, 13]. Probiotics can also increase the metabolism of host tissues, particularly the gastrointestinal mucosa and liver [14]. As research continues to uncover the critical link between gut microbiota and host health, the consumption of probiotics has increased significantly. While much attention has been focused on their beneficial functions, potential risks such as infections and the transfer of antibiotic resistance genes to pathogenic bacteria are often overlooked. Some studies have shown that probiotics may have harmful effects on the host. In case of immunocompromised states, D-lactic acidosis, brain fogginess, bacteraemia, and antibiotic resistance gene transfer could be found [15]. This review offers a comprehensive exploration of mechanistic approaches and contemporary perspectives on the therapeutic benefits of probiotics in disease prevention and treatment.

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Alam ST, Rayhan ABH, Ahmed MU, Khan MT, Jame JF, Islam MM, et al. Mechanisms of action and health benefits of probiotics: a comprehensive review. Explor Drug Sci., 2025;3:1008129, https://doi.org/10.37349/eds.2025.1008129

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