**5.4 Probiotics and human health**

Probiotics are usually linked to several health benefits, with most studies concentrating on the gastrointestinal (GI) tract but also showing promise in other regions of the body such as the respiratory system, vaginal tract, and subcutaneous tissue [42]. These advantageous characteristics vary depending on the strain, and while different attributes may be linked to a particular strain, numerous activities are frequently carried out through microbe interaction, either with one another or with the host [43]. They produce chemicals (antimicrobial substances) such as bacteriocins, which are naturally occurring antimicrobial substances that are typical of a proteinaceous nature with a lipid or carbohydrate moiety, or organic acids (specifically lactic and acetic acids, hydrogen peroxide, and so on) that lower the pH of the system during their colonization as well as other activities such as growth and metabolism [44]. These natural antimicrobials help to suppress infections. They can improve epithelial and tissue integrity and functionality during their stay in the gut, primarily by producing low levels of nitric oxide (NO), increasing mucus production, improving gut epithelial cell proliferation, inhibiting carcinogenic substance production or elimination through detoxification, and producing nutrients, particularly short fatty acids and vitamins [45]. Many different Lactobacilli and Bifidobacterium strains are presently available for use by humans in the inhibition and treatment of gastrointestinal (GI) infections [46]. Probiotics can promote intestinal health by regulating microbiota, stimulating and building the immune system, synthesizing and improving nutrient bioavailability, reducing symptoms of lactose intolerance, and lowering the risk of a variety of diseases [1]. During hydrolysis, several of these probiotics produce enzymes that have been demonstrated to improve protein and fat absorption. LAB, for instance, has been proven to boost vitamin B complex concentration in fermented

### *Lactic Acid Bacteria: Review on the Potential Delivery System as an Effective Probiotic DOI: http://dx.doi.org/10.5772/intechopen.111776*

foods [47]. Microorganisms acting in the digestive system or during the manufacture of cultured foods have been shown to increase the digestibility or absolute amounts of several dietary components, according to [47]. Probiotics offer a wide range of health and developmental benefits, some of which are discussed below. During fermentation, probiotics such as Lactobacillus can create enzymes such as lactase, which aid in the breakdown of lactose in dairy products. Lactose is a disaccharide that can induce intestinal distress in people with low levels of the intestinal enzyme lactase, resulting in bloating, gas, and abdominal pain [47]. Lactose intolerance is a genetic condition that affects around 75% of the world's population [48]. This condition limits the use of dairy products in a certain group of people. Lactobacillus, however, produces the enzyme known as lactase during fermentation, which hydrolyzes lactose into glucose and galactose for absorption. Kim and Gilliland discovered in 1983 that feeding lactose-intolerant individuals with fermented milk resulted in a significantly lower level of hydrogen in the breath when compared to individuals being fed with unfermented milk, and this low level of hydrogen indicates that lactose was metabolized before entering the large intestine.

Several probiotics have also been discovered to be added to the feed of animals to enhance the weight of these domestic animals. This weight gain was attributable to illness management and increased nutritional digestibility in the animals. Robinson and Thompson [49] conducted a study on humans and discovered that infants gained 21.9 oz. on average during their first month of life when fed a regular formula and 26.5 oz. when fed a special formula fortified with *L. acidophilus.* This research confirms that probiotics are useful in stimulating growth and development in young animals and individuals, according to evidence from different studies. By enhancing gut microbiota, restoring antioxidant systems, reducing insulin resistance and inflammation, and improving gut microbiota, probiotics also play a crucial role in the prevention of metabolic diseases including obesity, diabetes, and cardiovascular disease [50]. By competing with and sticking to the mucosal surface of the intestine and stimulating immunological responses, probiotics reduce intestinal infection and inhibit the development of Candida and *Helicobacter pylori* [51]. Some recommended microorganisms used as probiotics in both humans and animals and their health benefits are grouped in **Tables 1** and **2**, respectively.

### **5.5 Probiotics in cancer prevention**

The gastrointestinal tract (GIT) of humans serves as a "storage" for the rich and diverse collection of microorganisms (gut microbiota), predominantly bacteria. Through homeostasis and illness throughout human life, this group of microorganisms generally has a significant impact on the host [63]. The human system has around 10 times more prokaryotic cells than eukaryotic ones because of the presence of gut bacteria. Lactobacillus, Bifidobacterium, Lactococcus, Streptococcus, and Enterococcus*,* as well as some *Bacillus* and *Saccharomyces* strains, are among the numerous microorganisms found in the GIT [64]. However, many of the products from probiotic products currently found in the market these days contain more LAB from the genera Lactobacillus and Bifidobacterium [65]. These beneficial probiotic microorganisms impart and play a variety of roles in the human system, including cancer prevention and treatment. Cancer is defined as a disease that emerges because of uncontrollable cell growth and spreads to other sections of the body. This killer sickness has been one of the human battle diseases that, if not treated properly, can usually lead to death. However, there has been a scientific basis and proof that


#### **Table 1.**

*Microorganisms used as probiotics for humans and animals [50].*

probiotic bacteria, such as the above-mentioned strains, usually prevents or minimizes the formation of some group of cancers in the human body, and this is because members of the gut microflora can create carcinogens such as nitrosamines [1]. Numerous studies have also shown the possibility of probiotics for the prevention and treatment of cancer. Most of these studies focused on the modulation of the microbiota, the immune system, the reduction of bacterial translocation, the improvement of gut barrier function, the anti-inflammatory and antipathogenic activity, and the effects of probiotics on tumor growth and metastasis [65]. Verhoeven et al. [66] discovered that regular intake of probiotics (drink) for about 6 months increased the clearance of HPV and cervical cancer precursors in 54 women. Another group of researchers discovered that probiotics or synbiotics significantly reduced the activity of intestinal procarcinogen enzymes linked to colonic carcinogenesis in experimental animal models [67]. All these findings from different research sources propose and portray probiotics to be a good source of cancer inhibition and reduction in the human system, thus making these useful microbes for consumption especially strains from the Lactobacillus and the Bifidobacterium genera.

Additionally, LAB may influence the maturation of immune cells and their products not only in the gut but also in systemic immunological organs like the lymph node and spleen, resulting in tumor inhibition [65]. These data suggest that probiotics could be useful dietary supplements against neoplastic susceptibility due to their wide influence on the host's local and systemic immune mechanisms [68].

Another encouraging research was published in 1980 by Goldin and Gorbach, who were among the first to correlate Lactobacillus-rich diets to a decreased risk of colon cancer (by 37 percent compared to controls). Many *in vitro* studies have also indicated


#### **Table 2.**

*Probiotic bacteria and their health benefits.*

probiotics' therapeutic properties in regulating the growth and death of cancer cells such as gastric, colonic, and myeloid leukemia cells [69]. Despite this, many researchers have discovered that the *L. rhamnosus GG* strain has a significant antiproliferative effect and/or induces apoptosis in mus musculus colon carcinoma (HGC-27) and human colonic cancer cells (Caco-2, DLD-1, and HT-29) [70] as well as lowering the level of IL-8 [71].

The ability of probiotics to prevent the growth of colon cancer (colorectal) may be attributed to several mechanisms, some of which include modification of the intestinal microflora, inactivation of cancer-causing agents, competition with putrefactive and pathogenic microbiota, improvement of the host's immune system, antiproliferative effects such as regulation of apoptosis and cell differentiation, fermentation of undigested food, and inhibition of tyrosine [72].
