The prebiotics concept was proposed by British microbiologist Gibson in 1995 as a “non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria already resident in the colon”. Specifically, it is defined as a food ingredient that has the following criteria:

• It resists to host digestion (for example gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption).
• It modulates the composition and/or activity of the gut microbiota.
• It selectively stimulates the growth and/or activity of the intestinal beneficial bacteria.
• It facilitates the health of the host.

In recent years, a number of fermentable carbohydrates have been reported to show a prebiotic effect. These include non-digestible oligosaccharides, polysaccharides, and dietary fibers, and some of them are known as ingredients involved in Japanese Food for Specified Health Uses (FOSHU). Various effects of prebiotics have been reported, such as the growth of beneficial bacteria in the intestine, intestinal function, enhance immune function, prevent allergic conditions, increase of mineral absorption, anti-tumor, anti-obesity, and prevention of arteriosclerosis.

Milk oligosaccharides are milk components and oligosaccharides produced from them. They have long been studied as a factor that supports the growth of beneficial microorganisms in the body, and are used in foods and pharmaceuticals. In addition, human milk oligosaccharides (HMOs), which are contained in human breast milk, fulfill a variety of physiologic functions. Several studies have shown that HMOs are particularly important for the development of the newborn baby's intestinal microbiota and they can reduce the pathogen infections, support the immune system and improve the brain development.

Oligosaccharides are well known as a widely used food ingredient of prebiotics. There are various types of oligosaccharides including soybean-oligosaccharides, fructo-oligosaccharides, milk-oligosaccharides, galacto-oligosaccharides, xylo-oligosaccharides, and isomalto-oligosaccharides. Many of them are approved as ingredients of Food for Specified Health Uses in Japan.^†

Many of the polysaccharides and dietary fibers are energy sources for intestinal bacteria and indispensable elements for maintaining the gut microbiota. For example, indigestible dextrin is known to transport into the colon to be fermented by the gut microbiota, and galactomannan and amylopectin are reported to be selectively fermented by several bifidobacteria.