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:
1 kcal= 2.4 kJ
Daily Energy Requirements
These are affected by:
A balanced diet should contain: carbohydrates, protein, fat, vitamins, minerals, water and fibre.
Can be complex - eg starch or simple eg: fruit sugar (fructose)
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:
Proteins are made from chains of amino acids. First class proteins come from animal sources, second class proteins come from plant sources.
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 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 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.
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.
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 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.