Interactions of probiotics and prebiotics with the gut microbiota

Abstract

The gut microbiota (GM) composition varies among individuals and is influenced by intrinsic (genetics, age) and extrinsic (environment, diet, lifestyle) factors. An imbalance or dysbiosis is directly associated with the development of several illnesses, due to the potential increase in intestinal permeability leading to a systemic inflammation triggered by higher levels of circulating lipopolysaccharides and changes in the immune response caused by an overgrowth of a specific genus or of pathogens. These mechanisms may increase symptoms in gastrointestinal disorders or reduce glucose tolerance in metabolic diseases. Diet also has a significant impact on GM, and functional foods, namely prebiotics and probiotics, are a novel approach to reestablish the indigenous microbiota. Prebiotics, like inulin and polyphenols, are selectively utilized by GM, releasing short-chain fatty acids (SCFA) and other metabolites which may reduce the intestinal lumen pH, inhibit growth of pathogens, and enhance mineral and vitamin bioavailability. Probiotic microorganism may increase the microbial diversity of GM and improve the integrity of the intestinal barrier, leading to an improvement of baseline and pathologic inflammation. In this chapter, we will discuss the potential roles of prebiotics and probiotics in health and diseases throughout an individual's lifetime and proposed mechanisms of action.

Introduction

The term “microbiota” refers to the entire population of microorganisms in a given location. The largest population of microorganisms is the microbiota of the gut, which is comprised of more than 2000 bacterial species and is significantly influenced by intrinsic (genetics, age) and extrinsic (body mass index, smoking, physical activity, diet) factors, mainly by diet, which regulates microbial activity and gene expression (Fig. 1).1, 2, 3 Studies have shown that several diseases are associated with an imbalance of the bacterial composition of the gut, which is referred to as a dysbiosis. Dietary interventions may be effective in restoring it to a healthier state.⁴

In this sense, functional foods, which in addition to their nutritional properties must confer a defined benefit to the consumer's health, seem to be interesting alternatives for dietary interventions targeting at improving the microbiota shape. The most known functional foods or ingredients are polyphenol, polyunsaturated fatty acids, prebiotics, and probiotics.5, 6

Probiotics are defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.”⁷ While the definition of probiotics has been debated, an expert consensus from 2013 has agreed on this description.⁸ The major mechanisms of action of probiotics on human health are multifold and include competition with pathogens for nutrients and adhesion sites, production of bacteriocin, vitamins, and short-chain fatty acids (SCFA), immunomodulation, improvement of the intestinal barrier, and production of neurotransmitters.⁹

In the last years, studies related to probiotics and their effects on human health have increased exponentially. The vehicles or food matrices used to deliver probiotics affect the viability of the microorganisms and, therefore, have different impacts on the host microbiota. In addition, prebiotics and bioactive food compounds may interact with the commensal microorganisms that inhabit the human gut.

Several clinical trials have been conducted in order to evaluate the effect of probiotics, primarily those containing bacteria from the Lactobacillus and Bifidobacterium genera, on different food matrices and their impacts on the human health, leading to heterogeneous results. In this chapter, we will delve into different bioactive and probiotic foods and their effects on the human health.