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In all industrialized countries, there has been a notable increase in life expectancy over the past decade. Prolonged exposure to risk factors causing chronic diseases increases the probability of encountering clinical events. In this context, preventive treatments gain importance. Appropriate and continuous monitoring and control of risk factors plays a major role in preventing chronic diseases. For this purpose, lifestyle changes that include dietary improvement and adequate physical activity are necessary [1]. Healthy eating habits should be adopted. International health organizations suggest limiting the energy intake from fats, avoiding trans fatty acids, and choosing unsaturated fats in fat consumption. It is important that daily diets be enriched in vegetables, fruits, legumes, cereals, and nuts, and free sugar and salt intake should be limited [2, 3]. There are also strong recommendations about adding functional foods to one’s daily diet plan [1].

Although there are no generally agreed upon definitions of functional foods [4, 5], there are more than a hundred definitions proposed by various authorities and scientific organizations [5, 6]. The basic idea of functional foods is that of food or food ingredients with positive health influences for humans and/or the ability to decrease risks of chronic diseases [7, 8]. Functional products are specially designed for the reduction of cholesterol levels, blood sugar levels, blood pressure levels, and osteoporosis are on the market [8, 9].

Functional foods were first significantly improved in Japan as the first state to issue formal policies for their usage [10, 11]. These foods have long been key parts of Asian cultures [11, 12]. Besides Japan, Canada and the United States have the most active demand for functional foods, as consumers in these countries are open-minded about new foods and their legal framework is more appropriate than in Europe [11, 13, 14]. The large increase in functional food consumption in both the United States and Japan has additionally been supported by relevant public health authorities seeing these foods as potential means of lowering the expenses for public health [11, 15, 16]. European consumers, on the other hand, and especially those in the Mediterranean region, are often prejudiced against unfamiliar food items, even if the foods in question are labeled as having healthpromoting properties. While interest has been growing in the European markets for functional foods, problems of consumer trust constitute the largest obstacle to the spread of the use of these products [11, 17].

Functional foods are classified as foods with additional components or nutrients (e.g., juices that are supplemented with extra vitamin C, or the enrichment of various products with probiotics); foods whose unhealthy components have been removed, replaced, or reduced (e.g., fat from meat); and those with naturally enriched components (e.g., eggs guaranteed to possess higher levels of omega-3 fatty acid) [18, 19]. The basic ingredients used in functional foods are soluble fiber, probiotics and prebiotics, plant antioxidants, omega-3 polyunsaturated fatty acids, peptides, various vitamins and minerals, and amino acids [20]. Functional foods are not drugs such as pills or capsules; people consume them naturally within the course of their daily diets [20, 21].

There are many different functional foods on the market now. This field has been developed in different ways within the three main markets consisting of Japan, the United States, and Europe. In the first two of these, the leading functional food category is functional beverages (58%); in second place are cereals (United States, 17%) and confectionery products (Japan, 15%). In Europe, on the other hand, dairy products (46%) are the topselling functional foods, followed by cereal products (28%) [11].

Cereals are considered as functional foods because they provide antioxidants, dietary fiber, energy, protein, vitamins, and minerals that are necessary for human health [8, 22]. At the same time, they are valuable sources of phytochemicals including carotenoids, phenolic substances, vitamin E, sterols, resistant starch, and phytates [23–26]. Cereals can be utilized as fermentable substrates that allow probiotic microorganisms to successfully grow [8, 22]. Studies have shown that when bioactive compounds are included in cereals as complex mixtures, they may possess more healthpromoting properties than individually isolated components [25, 26]. Cereals also have the benefit of reducing consumers’ risks of chronic diseases by providing assorted health benefits beyond basic nutrition [23–26]. Wheat, buckwheat, oat, barley, flaxseed, psyllium, brown rice, millet, sorghum, maize, and rye may be listed as the most widely known functional foods of cereal origin. Epidemiological studies have indicated that consuming cereals regularly has the potential of reducing the risk of developing various chronic diseases, including arteriosclerosis, type-2 diabetes mellitus, coronary heart disease, and some cancers [27–33]. In particular, linoleic acid, vitamin E, fiber, folate, and selenium in cereals may be able to facilitate reduction of the risk factors for coronary heart disease. Furthermore, phytoestrogens, a type of lignin, are found in cereals, together with some phenolic acids that possess antioxidant properties. Decrease in cholesterol levels and the rate of fat absorption, the delay of gastric emptying, and the protection of the general health of the gastrointestinal system represent just a few of the health-promoting benefits of cereal consumption [22, 34]. For example, about 50 years ago, Trowell reported that the lower rate of ischemic heart disease in sub-Saharan Africa in comparison to Europe or the United States was a result of consumption of whole plant foods in the former region compared to refined products in the latter [33, 35], and the “fiber hypothesis” was accordingly formulated by Trowell and Walker and Burkitt [33, 36]. It should be kept in mind that processing generally decreases nutrient contents of cereals, thereby reducing their healthpromoting effects [33, 35].

Due to their beneficial activities in both treating and preventing many different diseases, and considering the increasing healthcare costs of modern times, the desire to better understand the potential of functional foods has increased among not only food scientists but among regulatory agencies, consumers, and food producers [37]. This chapter explores the structure, chemical compositions, and health-promoting effects of major cereals such as wheat, buckwheat, oat, barley, flaxseed, psyllium, brown rice, millet, sorghum, maize, and rye, and functional foods produced from these cereals.