Significance of Dietary Modulation of Intestinal Flora and Intestinal Environment

Abstract

The human intestines harbor 100 trillion viable bacteria, reaching 100 kinds, which consist of so-called intestinal flora. These bacteria grow on the food components ingested and bio-components secreted into the alimentary tract as nutrients. The composition of the intestinal flora can be altered by many factors such as aging, physiological state, drugs, various diseases, diet, and stresses, and has an influence on intestinal metabolisms, which have a great influence on nutrition, drug efficacy, physiological function, aging, carcinogenesis, immunity, infection and others in the host. Thus, it was revealed that the intestinal flora have a close relationship to both the health and diseases of the host. Furthermore, it was found that it is important to increase beneficial bacteria such as bifidobacteria and to decrease harmful bacteria such as clostridia among the intestinal flora for prophylaxis against geriatic diseases including cancers. It is now well established that foods and food components contribute to physiologic and biologic well-being. Optimal intestinal flora and intestinal environment are possibly achieved by a nutritionally well-balanced diet and the active intake of functional foods such as oligosaccharides, dietary fiber and fermented milks, which promote useful bacteria or suppress harmful bacteria. Recent advances of research in intestinal flora are the background for the appearance of functional foods. The functional foods are classified into 3 groups based on their mechanisms of action: “probiotics, ” “prebiotics” and “biogenics.” Probiotics are viable microorganisms, such as lactobacilli and bifidobacteria, which beneficially affect the host by improving the intestinal bacterial balance. Prebiotics are non-digestible food ingredients, such as oligosaccharides and dietary fiber, which beneficially affect the host by selectively stimulating the growth or activities of beneficial intestinal bacteria in the colon, and thus improve the health of the host. Biogenics include biologically active peptides, including immunopotentiator (biological response modifier: BRM), plant flavonoids, etc. They act directly or indirectly, through the modulation of intestinal flora, on health of the host. Probiotics and prebiotics act on the intestinal flora and improve the balance of the flora by enhancing the growth of beneficial intestinal bacteria and/or inhibiting the growth of harmful ones, resulting in scavenging in the intestinal environment. They often induce the production of biogenics such as antibacterial substances, immunopotentiators, etc. by the proliferation of beneficial intestinal bacteria. Thus, the functional foods enhance bio-regulation such as stresses, appetite and absorption, bio-defence such as immunity and anti-allergy, prevent diseases including diarrhea, constipation, cancer, cholesterolemia and diabetes, and suppress aging through immunostimulation as well as the suppression of mutagenesis, carcinogenesis, oxidation processes, intestinal putrefaction and cholesterolemia.