These days, healthy foods refer to functional foods that have positive effect on particular body functions, beyond the traditional nutritional effects. The ideal functional foods are the ones that are carrying bioactive components such as oligosaccharides, phytochemicals, dietary fibre, and active friendly bacteria or probiotics and include products like baked goods and cereals, baby foods, ready meals, snacks, dairy foods, confectionery, meat products, spreads, and beverages.

The term “functional foods” was introduced by the Japanese government in the mid-1980s and functional food concept obtained the legal status in 1991 by setting up “Foods for Specified Health Use” (FOSHU) regulatory system. Functional foods like conventional foods are eaten as a part of the normal diet but have additional physiological benefits. They can minimise the risk of chronic disease and maintain gut health because functional food supplies the human body with essential amount of fats, vitamins, proteins and carbohydrates, required for its healthy survival.

Functional foods are the food products which provide numerous health benefits on consumption beyond the traditional nutrients because of several bioactive components present in them. Several bioactive components in food include ?-3 and ?-6 polyunsaturated fatty acids (mainly conjugated linoleic acid and docosahexaenoic acid), polyphenols, probiotics/prebiotics, phytoestrogens, carotenoids, dietary fibre and phenolic acids.

PUFAs, the FAs with more than a single carbon–carbon double bond reported several beneficial effects include anti-inflammatory, immunomodulatory, cardioprotective, and antiatherosclerotic effects. Well-known examples of PUFAs are the long-chain ?-3 FAs, which are considered to be essential because they cannot be effectively synthesised by the body due to the low activity of the rate-limiting enzyme ?6-desaturase.

Phytochemicals are a group of plant secondary metabolites valued for their health benefits (e.g., as radical scavengers and quenchers of singlet oxygen). They have been shown to safely suppress pro-inflammatory pathways, reduce low-density lipoprotein (LDL) cholesterol, protect against damage caused by LDL cholesterol, and reduce the risk of atherosclerosis or plaque build-up in arteries that can lead to heart attack or stroke and contribute to CHD. Their antimicrobial properties may prevent the reversible and epigenetic changes in the body’s cells often linked to diseases.

Phytochemicals include flavonoids (flavanols, flavones, flavanones, isoflavones, catechins, anthocyanidins, and proanthocyanidins), carotenoids, as well as other polyphenols. Flavanols, flavones, and flavanones are the main flavonoids that occur in citrus. Several studies have suggested that the high concentrations of flavanols found in cocoa-rich products and dark chocolates increase the formation of endothelial nitric oxide, which promotes vasodilation and therefore may reduce blood pressure and risk of CVD.

Phytoestrogens are plant-derived phenolic compounds that are structurally and/or functionally similar to mammalian estrogens. They include isoflavones, coumestans, and lignans, which are most notably found in soybeans, clover and alfalfa sprouts, and oilseeds (such as flaxseed), respectively. Soybean is uniquely rich in the isoflavones genistein (4',5,7 trihydroxyisoflavone) and daidzein (4',7-trihydroxyisoflavone), and, to a small extent, glycitein.

Fibre, also known as “non-starch polysaccharide,” is derived from the cell wall of plants such as cellulose, hemicellulose, and pectin and is metabolised differently from other forms of carbohydrates, generally resistant to digestion and absorption. Fibre is further classified as soluble (food gums/hydrocolloids and pectin) and insoluble (cellulose and hemicellulose). The soluble components of the dietary fibre are degraded by microflora, resulting in a substantial stimulation of microbial growth and an increased faecal bulk.

Soluble fibre also affects glucose and lipid absorption into the bloodstream by lowering serum cholesterol. Insoluble fibre is resistant to breakdown by the microflora and has been identified for their role in laxation and bowel habit by retaining water within the cellular structure, intestinal transit time, production of short-chain FAs, and prebiotic effect. Their indigestible and fermentable nature mainly defines their nutraceutical and functional properties.

The FAO/WHO define probiotics as live microorganisms that when administered in adequate amounts confer a health benefit on the host while a prebiotic has been defined as a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth or activity of one or a limited number of bacteria in the colon and thus improves host health.

The importance of probiotics and prebiotics as nutraceuticals and functional foods stems from their ability to improve intestinal microflora, and to reduce and inhibit the growth pathogenic strains such as E. coli and Salmonella, allergic disorders, diarrhoea, and inflammatory bowel disease.