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Lesson 9 - Nutrition and Diet

Energy is obtained from the food we eat to maintain bodily functions, fuel muscular activity and for growth and repair of body tissues.

Energy is measured in calories (kilocalories) or joules (kilojoules). Average energy intake for men is 2300 kcal and for women, 1600 kcal in the UK. Energy comes from the following food types:

  • Protein - 4 kcal
  • Carbohydrate - 3.75 kcal
  • Fat - 9 kcal
  • Alcohol - 7 kcal (alcohol provides "empty" calories and is not an essential part of the diet)

1 kcal= 2.4 kJ

Daily Energy Requirements

These are affected by:

  • Age
  • Activity levels
  • Climate
  • Sex
  • Pregnancy and lactation
  • Bodyweight and body composition (muscle uses more calories than fat, even when not being exercised.)

A balanced diet should contain: carbohydrates, protein, fat, vitamins, minerals, water and fibre.

Carbohydrates

Can be complex - eg starch or simple eg: fruit sugar (fructose)
Can be unrefined eg wholemeal bread, brown rice or refined eg white bread, white rice
Complex carbohydrates include glycogen, (formed from glucose and also referred to as blood sugar), starch and fibre. Glycogen is stored in the muscles and the liver.

Carbohydrate Loading

Carbohydrate loading is a regime sometimes followed by athletes before an endurance event, to get an increase in muscle glycogen. A typical timetable would be:

  • Days 1-3 - eat little carbohydrate and exercise to deplete carbohydrate reserves
  • The body increase its supply of carbohydrates as it assumes they may be depleted again
  • Increase carbohydrate consumption and avoid exercise three days before the event
  • Carbohydrate levels are exceeded in time for the event.

Disadvantages:

  • Only works for a continuous, intense activity (over an hour)
  • A high heart rate must be maintained to avoid using fat for energy
  • For each gram of glycogen we carry 3 grams of water
  • Side effects include muscle lethargy, diarrhoea and chest pain.

Proteins

Proteins are made from chains of amino acids. First class proteins come from animal sources, second class proteins come from plant sources.

Fats

Fats are high in calories, but are necessary in a balanced diet. Saturated fat usually comes from animal sources and is solid at room temperature. A high intake of saturated fats is linked to coronary heart disease. Unsaturated fat usually comes from vegetables and is liquid at room temperature.

Vitamins

Vitamins are organic and found in plants and animals. They have no energy value. Vitamins A,D,E and K are fat soluble, whereas vitamins B and C are water soluble.

Minerals

Minerals are inorganic, have no energy value and are found in fruit and vegetables. Major minerals include calcium, magnesium, sodium, potassium and phosphorus. Trace minerals include iron, zinc and selenium.

A deficiency of calcium can lead to rickets in young people or contribute to osteoporosis in the elderly. A salt deficiency is unlikely in most people but can reduce the body's ability to sweat or produce urine. An iron deficiency can lead to anaemia and can be experienced by women of childbearing age, pregant women, children and vegetarians.

Water

The average adult should consume 2.5 litres of water per day, of which 1.8 litres should come from drinks. This should be increased during hot weather and during and after physical activity.

Type of Food
% of total daily energy intake
% according to OCR
Carbohydrate
47-50
55
Protein
10-15
15
Fat
35
30

General recommendations are to reduce salt in the diet, eat five portions of fruit or vegetables each day and eat sufficient dietary fibre (approximately 20 to 35 grams per day), which can be found in wholegrains, pulses and other fruit and vegetables.

Basal Metabolic Rate

The amount of calories needed for the body to "tick over" when no additional activity is taking place eg lying in bed. The value is aproximately 1.1 kcal / minute, but varies between individuals.

Fad Diets

Fad diets are usually not successful in maintaining weight loss, as they can be boring with a limited number of foods to choose from. It is better to adopt a lifelong healthy eating plan, together with exercise to increase calorie consumption and improve general fitness. High protein diets may lead to kidney damage and calcium loss in susceptible individuals.