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Diet and nutrition

Suzanne L. Noble

Introduction

Diet

In general, the term diet refers to food and drink consumption (diaita (Greek) ‘way of life’). The type of food and the amount eaten is an environmental factor in the aetiology of several diseases and variations in the morbidity and mortality between the world’s populations. More specifically the term diet is used to refer to a prescribed course of eating and drinking for therapeutic benefit. This involves regulation of the quantity, timing and category of food and drink, either under professional guidance or self regulated.

Nutrition

Nutrition refers to a process by which living organisms physiologically absorb and metabolise food to ensure growth, energy production, repair of tissue and ultimately reproduction of the species (nutritio (Latin) ‘to nourish’) (Macpherson, 1995). The intake of the appropriate requirements is essential for survival. According to Maslow’s hierarchy of needs (cited in Naidoo and Wills, 1998), basic physiological needs, such as hunger or thirst, must be satisfied first before an individual can find self-fulfilment. The science of nutrition includes the study of diets and dietary diseases.

The relationship between diet and disease

A ‘balanced’ diet refers to the minimum consumption of nutrients to provide the essential requirements of the body. Deficiency states, whilst no longer an overt problem in developed countries, continue to cause disease states in underdeveloped countries, due to famine or war. Where one or more of the essential nutrients are absent in the diet or there is inadequate absorption from the gastrointestinal tract, this is referred to as malnutrition.

Conversely, the majority of diet-related health problems in developed countries relate to excessive intake of essential and non-essential food and drink. Excessive consumption of refined carbohydrates, saturated fats, salt and alcohol have been linked to obesity, cardiovascular disease, high blood pressure, type 2 diabetes, dental caries and certain cancers. Obesity and malnutrition may occur in the same individual. Health promotion in affluent nations, in which these dietary components are freely available, is aimed at awareness and empowerment of the individual to eat a ‘healthy’ diet, i.e. one in which the essential nutrients are present but not consumed to excess. Education concerning obesity should be focused on awareness that food consumption must match physical activity. Current trends indicate that a third of the adult population will be obese by 2020. The dietary requirements of an individual throughout life are dependent upon the energy and growth requirements, for example during pregnancy, lactation and childhood. In addition the degree of physical activity and concomitant disease status must be considered. The ‘balance’ in the diet must take into account the dynamics of the human being.

Consumption of energy – basal metabolic rate

When the body is at rest a minimum amount of energy is needed to regulate involuntary life processes, such as:

• Respiration.
• Circulation.
• Digestion.

The basal metabolic rate (BMR) is measured by the amount of oxygen inhaled compared to the amount of carbon dioxide excreted. It is usually higher in women than in men.

Total energy output is made up of:

• BMR (70%).
• Physical activity.
• Thermogenesis.

Thermogenesis is the increase in energy output in response to food intake, cold exposure and psychological influences.

In general obese people have a higher BMR and total energy output than lean people. Obesity is graded according to a person’s weight in kilograms, divided by their height in metres squared, and is known as the body mass index (Table 7.1). Obese people do not appear to have a reduced capacity for thermogenesis.

Table 7.1 Classification of obesity.

Energy is measured in calories:

• Gram calorie (cal): the amount of heat required to raise 1 g of water 1 °C in temperature.
• Kilocalorie (kcal): the amount of heat required to raise 1 kg of water 1 °C in temperature.

In the moderately active woman, the BMR accounts for 1500 kcal a day out of a total daily energy expenditure of about 2300 kcal. For an average man the BMR accounts for 1600 kcal out of a total energy expenditure of 2500 kcal. Hence the proportion of energy expenditure by the BMR is approximately two thirds of the total.

The process whereby the energy derived from food products is made available to the various forms of work required by the body is known as metabolism. This can be subdivided into two separate processes:

• Anabolism: the constructive chemical and physical processes by which food materials are adapted for use by our body, e.g. amino acids to build proteins.
• Catabolism: the destructive process by which energy is produced with the breaking down of tissue into waste products.

Sources of energy are fat (9 kcal/g), alcohol (7 kcal/g), protein (4 kcal/g) and carbohydrates (3.75 kcal/g).

The current national dietary recommendations

A ‘balanced’ diet should include the following nutritional groups:

Dietary standards have been used in Britain since the 19th century and are published to improve the health of the nation. The recommended daily amount (RDA) dates back to 1979 and was meant to be applied to groups of people to minimise the risk of undernutrition and was set high compared with the average requirement. The Committee on Medical Aspects of Food Policy’s (COMA) Panel on Dietary Reference Values published their report in 1991. Dietary reference values apply to healthy people rather than those with diseases. The reader is recommended to review Scientific Basis of Nutritional Education: a Synopsis of Dietary Values (Health Education Authority, 1992), for specific detail, but dietary reference values are an estimate of the range of requirements of nutrients for a population or group and are intended for guidance. Such guidance is required for a scientific basis for food counselling, meal provision and food labelling. In this chapter the dietary reference values are given for the macronutrients. For the micronutrients the reference nutrient intake (RNI) is used, which represents the amount of nutrient which is sufficient for almost all individuals.

Macronutrients

Carbohydrates

Carbohydrates contain carbon, hydrogen and oxygen with the formula C_n(H₂O)_n. The term is applied because the hydrogen and oxygen are in the proportion to form water (hydrates). They should be the major source of energy in the diet (55%). They are broken down by enzymes to form simple sugars. Carbohydrates are stored in liver and muscle as glycogen, but excess is converted into fat for storage.

Carbohydrates can be classified as follows:

• Sugars: should make up no more than 15% of the carbohydrate intake and can be subdivided into monosaccharides and disaccharides.
• Polysaccharides: do not have the crystalline form of sugar, and are used in the human diet as a source of starch and roughage.

Consumption of sugars (refined carbohydrates) is a major aetiological feature in dental caries and is discussed later. A classification of carbohydrates and dietary sources is given in Table 7.2.

Table 7.2 Classification of carbohydrates and dietary sources.

The glycaemic index (GI)

The glycaemic index measures the rate at which glucose is absorbed through the intestine and its subsequent level in the blood. It runs from 0 to 100. The rate at which pure glucose is absorbed and raises the blood glucose level is given a score of 100. All other carbohydrate products are measured against this:

• High-GI foods: 70+.
• Medium-GI foods: 56–69.
• Low-GI foods: <55.

High-GI foods trigger the release of insulin for the removal of excess glucose from the blood for storage as glycogen or fat. Excess insulin is produced in response to a diet high in high-GI foods. Insulin excess creates hunger pangs and the desire to overeat. Low-GI foods are digested slowly and raise glucose level in the blood by a small amount, and hence only low levels of insulin are produced and the body feels satisfied for longer. Table 7.3 gives examples of high-, medium- and low-GI foods.

Table 7.3 High, medium, and low glycaemic index foods.

Fats (lipids)

Fats in the diet should be called lipids. They are a more concentrated source of energy than carbohydrates. They should make up no more than 30% of the diet of which a maximum 10% should be saturated fats.

Animal fat is a mixture of triglycerides:

• Stearic acid + glycerol.
• Plasmatic acid.
• Oleic acid.

Animal fats and dairy products are saturated fats. They are solid at room temperature. Vegetable oils are unsaturated fats, are liquid at room temperature and include soya bean, maize and sunflower. Fish oils are also unsaturated (e.g. cod liver oil).

The functions of fat are as follows:

• Energy source.
• Cushion to protect vital organs.
• Insulates the body by forming a layer under the skin.
• Carrier of fat-soluble vitamins A, D, E and K and carotene.
• Maintenance of cell membranes.
• Production of hormones, e.g. oestrogen.

Cholesterol

Cholesterol is a sterol, a waxy material derived from animal and vegetable tissues. It is essential in the body to the production of sex hormones and for repair of membranes. It is found in the brain, nervous tissue, adrenal glands and skin. Dietary sources are red meat, egg yolks and butter.

A high blood cholesterol level (i.e. > 6 mmol/l), is correlated with atheroma, which is associated with coronary thrombosis, high blood pressure and strokes. The liver can produce all the bodily requirements for cholesterol, but a high consumption of saturated fats leads to high blood levels of circulatory cholesterol.

Proteins

Proteins consist of chains of amino acids, linked together. Proteins constitute an essential part of the diet as a source of energy and for replacement and repair of tissues. Proteins contain nitrogen, which is an essential constituent of the body.

Proteins should make up about 12% of the diet. To be digested, proteins have to be broken down into the constituent amino acids. The adult human requires eight amino acids which it cannot produce or store and these are known as essential amino acids (Table 7.4). The body can produce non-essential amino acids, but a diet of mixed proteins is recommended for health. Protein for vegetarians is available as nuts, Quorn (yeast) and pulses. Examples of pulses are peas, beans and lentils. The soya bean is high in protein, and is available as tofu (soybean curd) and miso (fermented bean paste).

Table 7.4 Sources of essential amino acids.

The functions of proteins are:

• Growth, repair and maintenance.
• Energy source (after carbohydrates).
• Production of hormones and enzymes.

Micronutrients

Vitamins

Vitamin is a term that applies to a group of substances which are required in small amounts and are essential for growth and development. They exist in natural foods but most have been produced synthetically. The absence of vitamins leads to certain dietary diseases and growth retardation (Figures 7.1, 7.2 and 7.3). Many vitamins are coenzymes, which have an essential function in a chemical reaction catalysed by a specific enzyme. Vitamins are classified into fat-soluble A, D, E, K and water-soluble B complex and C. Table 7.5 outlines sources of vitamins, their function and deficiency states, including those of oral relevance.

Table 7.5 Sources of vitamins, their functions and deficiency states including those of oral relevance.

From Health Education Authority in: Scientific Basis of Nutritional Education: A Synopsis of Dietary Reference Values (1996), pp. 14–31. Reproduced with permission. © Crown Copyright.

Vitamins and antioxidant activity

Carotenes, including beta-carotene, vitamin C and vitamin E, are among the many substances in food that have antioxidant properties. This attribute can help to counter the effects of reactive oxygen species (free radicals) which are produced by the body’s normal metabolic processes. If they accumulate they can damage key cellular molecules, such as DNA and proteins. Cells with damaged DNA may be more prone to developing cancer. Free radicals readily oxidise polyunsaturated fatty acids in food and in cell membranes in the body to give lipid peroxides which can also damage cells. Peroxides, for example those formed by the oxidation of low-density lipoprotein (LDL) cholesterol, may play a part in the formation of the ‘plaque’ which can build up on the walls of the arteries and eventually cause heart disease.

People who consume large amounts of yellow fruits and dark green or orange vegetables seem to be less prone to some forms of cancer. Beta-carotene (but not preformed vitamin A) may play a role in the body’s natural defence mechanism against cancer by helping to destroy reactive oxygen species, but more research is needed to clarify this.

Vitamin C may also form part of the body’s defence against the harmful effects of reactive oxygen species. It may work directly by destroying free radicals, indirectly by helping to reactivate vitamin E, or in both of these ways. Research is continuing into the possible role of vitamin C in the prevention of heart disease and cancer.

Alpha-tocopherol (and to a lesser extent other tocopherols) can help prevent the oxidation of LDL and the formation of free radicals that may damage cells and cause heart disease.

People at risk of vitamin deficiency

These include:

• Anorexics and bulimics.
• People suffering from Crohn’s disease and other intestinal diseases affecting absorption of nutrients.
• Vegans and vegetarians.
• Low socioeconomic groups.
• The elderly.
• People with liver disease, including alcoholics.

Vitamin supplements – are they necessary?

Most people should be able to obtain their vitamin requirements by eating a healthy balanced diet. Vitamins are only needed by the body in small amounts and high doses can be harmful. Taking vitamin supplements is not a substitute for an unhealthy diet. Fruit and vegetables are a good source of water-soluble vitamins but they also contain fibre and antioxidants, which are not provided by a vitamin tablet. There is currently no evidence that vitamins prevent colds and, until such time as the evidence proves that vitamin supplements are beneficial to the healthy person, they are best avoided. Some groups, such as pregnant women, vegans, etc., may benefit after consultation with a physician.

Minerals

Minerals are inorganic substances, which are required in the structural composition of the hard and soft body tissues. They also participate in the contraction of muscles, nerve conduction and blood clotting. They are classified into major and minor (or trace) elements. Table 7.6 gives sources of minerals, their function and deficiency states, including those of oral relevance.

Table 7.6 Sources of minerals, their function and deficiency states, including those of oral relevance. Minor elements include copper, zinc, fluorine, chromium, molybdenum and selenium, which are components of many enzymes and are essential in trace amounts.

From Health Education Authority in: Scientific Basis of Nutritional Education: A Synopsis of Dietary Reference Values (1996), pp. 14–31. Reproduced with permission. © Crown Copyright.

Water

Water is not formally a nutrient but additional sources of water are essential in the diet. As 65% of body weight is water, a 10% loss can cause metabolic problems or even death. The recommended daily intake is 1–2 litres and the body can only survive a few days without water. There is increased demand in hot climates, following strenuous exercise, in times of fever and in diarrhoea and vomiting. It has become fashionable to drink bottled water which may be carbonated at source or by the manufacturer before bottling. Mineral waters contain calcium, hydrogen sulphide and sodium. People with oedema, high blood pressure or heart diseases should check the sodium levels of bottled water. Excessive intake of carbonated water may lead to enamel erosion.

The functions of water in the body are:

• A carrier of nutrients and waste products to and from cells.
• Helps regulate body temperature.
• Essential to digestion and metabolism.
• Lubricates the joints, nervous system and eyes and aids respiration.

Summary

In summary, the Food Standards Agency (FSA) states that the key to a healthy diet is to eat a variety of foods, which for most people means eating:

• More fruit and vegetables.
• More bread, cereals and potatoes.
• Less fat, sugar and salt.
• A third of their diet made up from bread and cereals, choosing wholegrain, wholemeal, brown or ‘high-fibre’ varieties whenever possible.
• At least five portions of fruit and vegetables every day, including fresh, frozen, tinned, dried or juiced. Fruit and vegetables should make up about a third of food eaten each day.
• A moderate amount of meat, fish and alternatives such as pulses, eggs, nuts and beans, choosing lower-fat versions when possible. At least two portions of fish per week should be eaten, one of which should be oily fish.
• Less fatty and sugary foods and drinks, such as margarine, butter, cream, chocolate and biscuits, soft drinks, sweets, jam, cakes and ice cream.
• Milk, cheese, yoghurt, fromage frais and other dairy products in moderate amounts, choosing lower-fat varieties whenever possible.
• Less salty foods. Most adults are eating too much (on average 9 g of salt per day (two teaspoonfuls) which should be reduced to less than 6 g). Most (about 75%) of the salt in our diets comes from processed foods.

Alcohol

Alcohol has no nutritional value and is a drug. If it is drunk to excess it may be a contributory factor in systemic and oral diseases. The reader is directed to Chapter 11, p. 236 for further details.

Figure 7.4 is a pictorial representation of a balanced diet, published by the Health Education Authority.

Dietary requirements of groups with special needs

Pregnancy and lactation

A woman’s nutritional needs increase during pregnancy and lactation. This is necessary to provide for the development of the child and to meet the physiological changes of the mother’s body. These need to be provided by an increased intake of essential carbohydrates, proteins, iron, calcium and folates and vitamins C and D. In the final 3 months of pregnancy, an additional 200 kcal are required daily, and in lactation 500 kcal extra a day. There is some evidence that vitamin D deficiency in pregnancy can cause enamel hypoplasia and thus predispose to caries in the deciduous dentition (Rugg-Gunn, 1993). In the case of calcium deficiency in the mother, calcium cannot be removed from the calcified tissues of her teeth, and any increase in caries is due to a high-sucrose diet. Vomiting in early pregnancy is a frequent symptom and the dental hygienist/therapist has a role to play in giving advice about the avoidance of dental erosion.

Weaning

Good nutrition is essential to the development of the primary and secondary dentitions. Solid food is usually introduced at 3 months and before 6 months of age. Breast-fed babies tend to have a lower dental caries experience than bottle-fed babies. Milk has a low cariogenicity factor but if mothers add sugar to the bottle or supplement the bottle with reservoir feeders containing fruit syrup, there is a strong relationship between their use and the incidence of de/>

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