and beverage recommendations for populations; aiming to promote a diet that meets the nutrient requirement, and to prevent diet-related diseases such as dental caries and obesity. Based on the amount required by the human body for normal metabolism, growth and physical well-being, nutrients are divided into 2 categories: macronutrients consisting of proteins, carbohydrates and fat; and micronutrients consisting of vitamins and minerals. Fats are the most energy-dense macronutrient; whereas carbohydrates are quantitatively the most important dietary energy source for most populations. Proteins are vital structural and functional components within every cell of the body and are essential for growth and repair and maintenance of health. Vitamins and minerals, which are found in small amounts in most foods, are essential for normal metabolic function. This chapter provides an overview of the impact of nutrients on general and oral health, with an emphasis on macronutrients.
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Introduction
Diet and nutrition are fundamental in maintaining the general and oral health of populations. Diet refers to the total amount of food consumed by individuals, and consists of different constituents which can be governed by many factors such as environmental conditions and availability of food, religious beliefs, socioeconomic status, and so on. Nutrition is the process of utilising food for growth, metabolism and repair of tissues, and involves ingestion, digestion, absorption, transport, incorporation into cells, and excretion. The main dietary patterns include: omnivorous (a mixed diet of both plant and animal origin), flexitarian (a plant-based diet with occasional animal protein consumption), pescatarian (a plant-based diet with a restriction of animal protein consumption to fish and seafood only), pollotarian (a plant-based diet with a restriction of animal protein consumption to poultry and fowl only), lacto-ovo vegetarian (a vegetarian diet with inclusion of dairy products such as cheese, milk and yogurt), and vegan (a restricted vegetarian diet with exclusion of any animal product or their by-products such as gelatine). Convenience, life style, nutritional status, health and weight management are among the factors which passively influence the dietary pattern of each individual.
Fig. 1. Eatwell Guide of Public Health England [1].
The relationship between diet and nutrition and health is 2-way. Health status can be affected by nutrient deficiency and vice versa, that is, any health problem (including oral health) may affect nutritional status. The main nutrients required to maintain general and oral health are proteins, carbohydrates, fat, vitamins and minerals. Many health conditions such as obesity, diabetes, cardiovascular disease, several forms of cancer, osteoporosis and dental disease can be avoided by having a well-planned nourishing diet. A “Balanced Diet” consists of a variety of different types of food that provides sufficient amounts of nutrients required to maintain good health. All over the world, dietary guidelines have been produced by governments to provide evidence-based food and beverage recommendations for populations. These recommendations aim to promote a diet that meets the requirement for energy as well as all essential nutrients to prevent diet-related diseases such as obesity and dental caries. Examples of such guidelines are the “Eatwell Guide” recommended by Public Health England (Fig. 1) [1] and the Healthy Eating Pyramid of the Australian Nutrition Foundation [2]; illustrating different types of foods and drinks and the proportions in which they should be consumed. These guidelines are based on human nutritional requirements and dietary recommendations which are termed Nutrient Reference Values in Australia [3], Dietary Reference Values in the UK [4, 5], and Dietary Reference Intakes in the USA [6]. These values are general terms comprising a series of estimates of the amount of energy and nutrients required by healthy individuals of different age groups (Table 1).
Table 1. Terms of reference values for food energy and nutrients for groups of people in Australia, the UK, and the USA
Nutrients are divided into 2 categories, macronutrients and micronutrients, based on the amount required by the human body for normal metabolism, growth, and physical well-being. The impact of specific nutrients on oral health is discussed in detail in Chapters 3–6.
Macronutrients
Carbohydrates
Carbohydrates are quantitatively the most important dietary energy source for most populations, usually contributing 55–75% of total daily energy requirements [7]. They are predominantly derived from plant foods, with grains and fruits as well as dairy products as the main dietary sources.
Carbohydrates are composed of carbon, hydrogen, and oxygen in a ratio of 1:1:2, respectively. In early nutrition text books, carbohydrates were classified into 2 groups: simple carbohydrates composed of monosaccharides (glucose, fructose and galactose) or disaccharides (sucrose, lactose and maltose), which are easily and quickly utilised for energy by the body, and complex carbohydrates (oligosaccharides and polysaccharides) which take longer to digest. Carbohydrates are also often classified into 3 groups: (i) monosaccharides, (ii) disaccharides and oligosaccharides, and (iii) polysaccharides [8]. However, based on a Food and Agriculture Organization and World Health Organization joint recommendation [9], dietary carbohydrates should be classified into 3 groups based on their chemical forms (Fig. 2), as determined by the degree of polymerisation, type of linkage (a or non-a) and character of individual monomers. The precise division between these groups is not quite helpful as the physiological and health effects of carbohydrates are also determined by their physical properties, which include water solubility, gel formation, crystallisation state, association with other molecules, and aggregation into the complex structures of the plant cell wall [9]. In any case, the importance of these categorisations is insignificant for determining the nutritional quality of carbohydrates; for example, fructose (a simple carbohydrate) increases blood glucose slowly, whereas processed starches (complex carbohydrates) raise blood glucose rapidly. Glycaemic index (GI) was therefore introduced to classify different sources of carbohydrate-rich foods according to their effect on post-meal glycaemia [10]. In this categorisation, carbohydrates are ranked on a scale from 0 to 100 based on how quickly and how much they raise the levels of blood glucose after consumption: low GI (0–55), medium GI (56–69) and high GI (70–100), where low-GI foods are those being digested and absorbed slowly and high-GI foods are rapidly digested and absorbed.
Fig. 2. Major dietary carbohydrates.
The metabolism of carbohydrates starts in the mouth with mechanical and chemical digestion; mastication grinds the food into smaller fragments and salivary amylase breaks down amylose and amylopectin into smaller chains of glucose, called dextrins and maltose. Since only about 5% of starch is broken down in the mouth, starchy foods