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Principles of nutrition, nutritional surveillance and assessment in specific populations including its short and long term effects

Health and Social Behaviour: Principles of nutrition, nutritional surveillance and assessment in specific populations including its short and long term effects

Principles of nutrition

Definitions

Nutrition is the study of the influence of food intake on health and wellbeing.

Public health nutrition involves studying the relationship between dietary intake and disease (nutritional epidemiology) and applying the knowledge gained to help prevent disease in the population (nutrition intervention).

Dietetics is the application of nutritional knowledge particularly tailored to individual needs. It generally involves the use of diet in the treatment and management of disease.

Energy

  • Energy is needed by the body for a number of functions.
  • Energy is provided by the diet (food and drinks) in the form of carbohydrate, proteins, fats and alcohol.
  • Energy can be measured in either joules (J) or calories (cal). One calorie is equivalent to 4.184 joules or one kilocalorie (kcal) is 4.184 kilojoules (KJ).
  • The amount of energy made available to the body by carbohydrates, proteins, fats and alcohol varies: per gram of carbohydrate (starch and sugar) provides 16KJ (3.75 kcal), per gram of protein provides 17KJ (4 kcal), per gram of fat provides
    37KJ (9kcal), and per gram of alcohol provides 29KJ (7 kcal). Summary provided in table 1.

    Table 1: Amount of energy made available by different sources of energy 

    Energy Source (per gram)

    Kilojoules (KJ)

    Kilocalories (kcal)

    Carbohydrate

    16

    3.75

    Proteins

    17

    4

    Fats

    37

    9

    Alcohol

    29

    7

     

  • Energy balance occurs when energy intake (food and drinks consumed) equals energy expenditure. An individual in energy balance will maintain their weight. Increases in energy intake/decreases in energy expenditure will lead to weight gain and
    decreases in energy intake/increases in energy expenditure will lead to weight loss.
  • Energy expenditure is primarily determined by body size, body composition and physical activity.
  • The actual amount of energy needed will vary from person to person and depends on their basal metabolic rate (BMR) and their level of activity.
  • Energy requirements increase by approximately 800 KJ/day in the last trimester of pregnancy, and by about 2100 KJ/day during full lactation.

Carbohydrate

  • Carbohydrate is needed by the body’s tissues for energy.
  • There are two main types of carbohydrates: sugars and starch. Both sugars and starch provide energy.
  • Sugars can be subdivided into intrinsic and extrinsic. Intrinsic sugars are those that are part of the cellular structure of foods e.g. sugars in fruits and vegetables. Extrinsic sugars are those that are not part of a cellular structure e.g.
    lactose in diary products, or honey, fruit juices and confectionary (also known as non-milk extrinsic sugars).
  • Complex carbohydrates include starch and non-starch polysaccharides. Starch is found in potatoes, bread, rice and pasta and non-starch polysaccharides are found in fruits, vegetables, legumes and whole-grain cereals.   
  • Fibre is a type of carbohydrate found only in plants. Fibre cannot be digested so it does not provide energy but is needed for a healthy digestive system.
  • At least half the energy in our diets should come from carbohydrate, mostly as starchy carbohydrates.
  • Frequent consumption of food and drinks containing non-milk extrinsic sugars can increase risk of tooth decay.

Protein

  • Protein is needed by the body for growth and repair and is able to provide energy when the diet is low in carbohydrate.
  • Protein is found in animal and plant cells in a variety of foods e.g. meat, fish, eggs, dairy, cereals, nuts and pulses.
  • Proteins are made up of amino acids. There are approximately 20 different amino acids found in foods.
  • Amino acids are broken down into 2 groups: essential and non-essential.
  • Essential amino acids are those that must be supplied by the diet: Leucine, Isoleucine, Valine, Threonine, Methionine, Phenylalanine, Tryptophan, and Lysine.  Histidine is an essential amino acid for children (not adults) because
    children are unable to produce enough to meet their needs.
  • Non-essential amino acids are those that the human body is able to make itself (by breaking down amino acids in protein that are eaten and absorbing them to make other proteins in the body).
  • Different foods contain different amounts and combinations of amino acids.
  • Vegans and vegetarians can get all the protein they need by combining different plant sources of protein, e.g. pulses and cereals.

Fat

  • Fat is needed by the body for energy, for providing essential fatty acids, and for carrying and absorbing fat-soluble vitamins (A, D, E and K). 
  • Fat is found in meat/meat products, dairy products, fish, eggs, fruit, vegetables, nuts, cereals and cereal products (including cakes and biscuits), savoury snacks and oils.
  • Fats are described as either saturated or unsaturated depending on the proportions of fatty acids present. Butter is described as a saturated fat because it has more saturated fatty acids than unsaturated fatty acids.  Olive
    oil is described as an unsaturated fat because it has more mono- and polyunsaturated fatty acids than saturated.   
  • Saturated fats are usually found in animal products and unsaturated fats in vegetable sources. There are exceptions to this rule.  Unsaturated fats may be converted into saturated fatty acids by hydrogenation.
  • Essential fatty acids (EFAs) are those that must be supplied in the diet because the body is unable to make them. There are two essential fatty acids: alpha linolenic acid (n-3) and linoleic acid (n-6). The body is able to
    synthesise other fatty acids from these two essential fatty acids.
  • Fat should not exceed more than one third of a human being’s energy intake and a high intake of saturated fat can have adverse effects on health.

Vitamins

  • Vitamins are nutrients that are needed by the body in very small amounts for a variety of functions carried out by the body e.g. co-factors in enzyme activity and antioxidants. 
  • Different foods supply different amounts of vitamins.
  • Vitamins needed by the body include: vitamin A, D, E, K (fat soluble vitamins), C, B1, B2, Niacin, B6, B12, Folate (water soluble vitamins).
  • Vitamins, except vitamin D, have to be provided by the diet because the body is unable to make them.
  • Vitamin D can be produced by the action of sunlight on the skin.
  • Each vitamin is required in different amounts for a number of different processes in the human body.
  • The amount of each vitamin needed by the body changes during a person’s lifetime.

Minerals

  • Minerals are nutrients that are needed by the body for a variety of functions e.g. formation of bones and teeth, as an essential constituent of body fluids and tissues, for nerve function and components of enzyme systems. 
  • Different foods supply different amounts of minerals.
  • Minerals needed by the body include: calcium, magnesium, phosphorus, sodium, potassium, chloride, iron, zinc, iodine, fluoride, selenium, copper, chromium and manganese. 
  • Each mineral is required in different amounts for a number of different processes in the human body. Some minerals are needed in large amounts (e.g. calcium, phosphorus, magnesium, sodium, potassium and chloride) and others in smaller amounts
    (e.g. iron, zinc, iodine, fluoride, selenium and copper).
  • The amount of each mineral needed by the body changes during a person’s lifetime.

Water

  • Over half the human body consists of water, and regular fluid intake is essential for the correct functioning of the body.  For example, it acts as a lubricant for joints and eyes, helps for swallowing, provides a medium in which most
    reactions in the body occur, helps eliminate waste, helps regulate body temperature. 
  • The amount of fluid needed varies between people and according to age, time of year, climatic conditions, diet and levels of physical activity.
  • Water can be obtained from the direct consumption of water and other drinks (e.g. squash, tea, coffee) and through the consumption of food (e.g. fruits and vegetables).

The Eatwell Plate, formerly the Balance of Good Health, has been designed by the Food Standards Agency to make healthy eating choices easier to understand for individuals (http://www.food.gov.uk). 
The plate is a visual representation of the five types and proportions of food people need to maintain a healthy and balanced diet.  The five types are broken down into the following categories:

  1. Fruit and vegetables
  2. Bread, rice, pasta, potatoes, and any other starchy foods
  3. Milk and dairy foods
  4. Meat, fish, eggs, beans, and any other non-dairy sources of protein
  5. Foods and drinks high in fat and/or sugar.

Food that represent the largest groups/proportions in the Eatwell Plate should be eaten most often, and food from the smallest groups/proportions should be eaten least often.

Nutritional surveillance and assessment in specific populations including its short and long term effects

Nutritional surveillance involves the routine collection and collation of data which inform us about the nature and causes of nutritionally related disease. Initially, these were diseases arising from nutritional deficiencies (e.g. anaemia,
rickets, and osteoporosis) but they now include a whole range of conditions (e.g. obesity, hypertension, cancers, coronary heart disease, and dental caries).

Nutritional surveillance traditionally involved only dietary surveillance by evaluating national food productions, household expenditure on food, household studies of food purchases and consumption and occasionally studies of individual
consumption. These contribute to the Food and Agriculture Organisation’s data on national food balance sheets. A surveillance system that links dietary and health surveillance (using indices of health such as weight, blood pressure, serum
cholesterol and anaemia) allows more effective evaluation of the dietary contributors to diseases such as obesity, diabetes, hypertension and cardiovascular disease. In the UK, the National Diet and Nutrition Survey (see Markers of nutritional
status, nutrition and food) links diet with indices of health. It was established to compare current intakes of nutrients with the various Dietary Reference Values (DRVs) to assess where problems exist in the population (e.g. high salt intake and low
consumption of fruit and vegetables) and to assist with informing government policy.

Surveillance can identify short-term nutritional effects which includes those conditions that are responsive to acute changes in diet:

  • High intake of sugary foods – increased dental caries
  • High intake of salt – increased blood pressure

Surveillance can also identify long-term nutritional effects, which includes those conditions that may not occur for several decades:

  • Lack of fruit and vegetable intake – colon cancer
  • High and prolonged intake of alcohol – colon cancer
  • Lack of breastfeeding – breast cancer
  • Central obesity – type 2 diabetes
  • Lack of dietary calcium – osteoporosis

References

  • British Nutrition Foundation http://www.nutrition.org.uk/ [accessed 01.08.08]
  • Food Standards Agency http://www.food.gov.uk/ [accessed 01.08.08]
  • Food and Agriculture Organisation of the United Nations http://faostat.fao.org [accessed 01.08.08]
  • Garrow J., James W. and Ralph A .Human Nutrition and Dietetics (10th Edition)
  • Lewis, G. Sheringham, J. Kalim, K. Crayford, T. Mastering Public Health: A postgraduate guide to examinations and revalidation. The Royal Society of Medicine Press Limited.

© Hannah Pheasant 2008