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FOR TEENS - The Basic Food Groups
 
“The ratio of food which supply our daily needs should reflect the groups in the food pyramid. A balanced diet will include six daily servings of complex carbohydrates; five servings of fruit or vegetables; two servings of milk; two servings of protein; and 15 – 25 gm of fats and oils”.
 
The human body is made up of millions of molecules, water being the most abundant component. We need a constant flow of food and its nutrients to maintain life and promote cell, organ and tissue growth. Food also provides us with energy, required for every thought and action that we perform all day.

Proteins, fats and carbohydrates are “macronutrients”, required in large quantities. Minerals and vitamins are “micronutrients” and although crucial to our health, only small quantities are required.

 
Carbohydrates
 

“In previous decades, starchy carbohydrates such as bread ,pasta, potatoes and rise were considered to be fattening, stodgy and generally unimportant foods. The modern view is, that they are an essential and vital part of a balanced diet.”

Carbohydrates are made by plants from sunlight and are our main source of energy. One gram of carbohydrate releases four calories of energy.

Carbohydrates are classified into the following categories:

a) Sugars, based on their structure, are divided into two groups, namely the ‘monosaccharides’ and the ‘disaccharides’.

The monosaccharides consist of:

  • glucose (the principle sugar used for energy purposes)
  • fructose (found in fruit and referred to as ‘fruit sugar’)
  • galactose (derived when the sugar molecule lactose is broken down).

The disaccharides consist of:

  • lactose (milk sugar, and the only sugar of animal origin)
  • sucrose (also called ‘white sugar’ or ‘table sugar’)
  • maltose (malt sugar found in beer and breakfast cereals).

b) Starches (also called ‘polysaccharides’) are composed of long chains of glucose. Like some types of sugars, starches require special enzymes to separate the individual glucose molecules from one another, before they can be utilized as an energy source.

c) Fibre is more complex in structure than sugars and starch, and humans, unlike rodents and herbivores, lack the required enzymes for its digestion. A large proportion of fibre therefore passes through our gut, mostly undigested, but aids with the very important function of elimination.

There are two types of fibre naturally found in foods.

Insoluble fibres (cellulose, hemicellulose) are found mainly in unrefined grains (digestive bran, whole wheat flour, brown rice, wholegrain breakfast cereals) and also in some fruit and vegetables (cabbage, peas, beans, apple skins.) This kind of fibre is not so readily broken down in the bowel by bacteria, and increases the bulk and water content of stool, thereby stimulating natural bowel movements.

Soluble fibres (pectins, gums, mucilages) are found mainly in fruit and vegetables (apples, citrus fruit, strawberries, sweet corn, broccoli, dried fruit, pears), and in grains, legumes and nuts (oat-bran, oats, peas, lentils, beans, peanuts, almonds.) This kind of fibre is rapidly broken down by bacteria in the bowel. The additional benefit of consuming soluble fibre is that it delays stomach emptying, thereby promoting satiety (feeling of fullness). It also slows the absorption of glucose from the small intestine, preventing a surge in insulin levels, resulting in better Glycaemic control. Soluble fibre is also responsible for lowering blood cholesterol levels, and is therefore beneficial in preventing heart disease.

As the principle source of energy, glucose requires special attention.

After a meal, all excess glucose molecules not required for immediate energy purposes are bonded together via a chemical process into one long chainlike molecule called ‘glycogen’. Glycogen, in turn, is stored in two ‘pantries’ in the body, namely the liver and the muscles. These ‘pantries’ have limited cupboard space, and once full, all excess glucose molecules are converted into molecules called ‘fatty acids’. Fatty acids are then bonded together as ‘triglyceride’ molecules and transported to a much larger storeroom with unlimited space, namely the fatty tissue. The hormone that is responsible for this process is called insulin.

Besides contributing to weight gain by stimulating fat production, fat transportation and fat storage, insulin also blocks the natural flow of fatty acids from the fatty tissue to other cells to be used for energy purposes, thus preventing you from losing weight.

Blood insulin levels are controlled by blood glucose levels. The faster and higher blood glucose levels rise, the more insulin is released. The Glycaemic Index (GI) is a new classification of carbohydrates based on the speed of which individual food items release glucose into the system and, therefore, their ability to raise blood glucose levels. Food items with a high GI value raise blood glucose levels much faster than food items with a low or intermediate GI value. If glucose enters the system at a slower rate, less insulin is also secreted. The result is that less fat is deposited.

Various factors affect the Glycaemic Index of food. Individual properties relating to each food substance, the presence of fat, fibre and protein in meals (mixed meals) and different food production or processing techniques are primarily responsible for these variations.

To avoid a sudden rise in blood insulin, one should eat carbohydrates from the low to intermediate GI groups, in preference to high GI carbohydrates.

 
Protein
 
Essential for most of body’s vital functions, including the growth, maintenance and repair of cells. It also helps to create enzymes that enables to digest food, produce antibodies that fight off infection, and hormones that fight off infection.’

Like carbohydrates, dietary protein supplies four calories of energy per gram.

All proteins are constructed from smaller sub-units called amino acids. There are 22 different types of amino acids and each amino acid has its own individual structure, function and property. Most amino acids can be manufactured in the human body, but ‘essential amino acids’ are those our bodies cannot synthesize on its own, and that we must acquire from our diet.

Meat, dairy and eggs have the entire range of amino acids, and are therefore called ‘complete proteins’. Although some plants have substantial quantities of proteins, they do not always contain the entire range of amino acids, and are therefore sometimes referred to as ‘incomplete proteins’. Vegetarians must therefore combine different plant products (such as legumes with grains) to ensure the intake of the entire range of amino acids. Most amino acids are beneficial to the body. The amino acid ‘homocysteine’, however, plays an important role in the development of hardening of the arteries, and raised homocysteine blood levels are therefore detrimental.

After water, protein is the most abundant substance in the body. It is the primary component of our muscles, skin and internal organs. Amino acids, unlike carbohydrates and fat, are not stored in the body for energy purposes, but can be used for energy in certain conditions. During a period of famine, for example, the body will first use carbohydrate and then fat for energy purposes. Only when these stores are depleted, will the body start using its own protein.

It is of interest that dietary protein from food sources do not stimulate the release of insulin, hence the popularity of the ‘ketogenic’ or ‘high protein’ diets.

 
Fat
 
“The role of fats in the diet has excited much controversy and debate in recent years. Eating too much of certain types is harmful but others are vital for the body and can prevent disease.”

The main function of fat is to store energy. It does this so well that one gram of fat contains nine calories of energy, more than twice the amount that carbohydrate and protein contains.

As a minor function, fat also serves to insulate the body against cold. (An irritating function of improved insulation is that less energy is burnt to preserve or maintain body temperature).

All fats consist of smaller sub-units called ‘fatty acids’, which are in fact just large molecules made from carbon and hydrogen atoms. A ‘saturated fat’ contains the maximum number of hydrogen atoms it can accommodate. It is therefore ‘saturated’ with hydrogen. An ‘unsaturated fat’ simply has space for more hydrogen atoms, and is therefore ‘unsaturated’ with hydrogen. For various medical reasons, unsaturated fats are beneficial to our health, whilst saturated fats are detrimental to our health.

Some fatty acids play a crucial role in the human body, and are called ‘essential fatty acids’ (EFA’s). Because of these benefits, they should ideally be consumed on a daily basis, and without an adequate supply of these certain disease processes may develop.

 
Vitamins
 
Vitamins are not sources of energy and contain no energy value.

They are also not building blocks and do not form part of the structure of our bodily tissues. They do, however, have a very important function, and assist other chemicals such as enzymes and hormones when performing a variety of metabolic and biochemical tasks. They are therefore ‘co-enzymes’, and are essential for growth, vitality and health. They also assist with digestion and elimination, as well as resistance to disease (immunity).

Our bodies cannot manufacture vitamins, and we therefore need to ingest them by eating plants and animals that manufacture them.

Water-soluble vitamins include many of the B vitamins and vitamin C. They are not stored in the body, and should ideally be consumed on a daily basis.

Fat-soluble vitamins are vitamin A, D, E and K, and are found in the fatty component of both vegetable and animal-source foods. These vitamins can be stored in the fatty tissue of the body, and have therefore the potential to accumulate and become toxic.

The shortage of certain vitamins can cause disease and increase the risk of developing many degenerative conditions.

 
Minerals
 
Like vitamins, minerals are not sources of energy and contain no energy value. They are, however, extremely important and assist the body with energy production.

Minerals, also known as elements, are basic molecules that cannot be reduced to simpler substances. Almost all the Earth’s minerals are present in our bodies, but some minerals are considered essential if a deficiency produces symptoms or illness. These essential minerals can be divided into bulk minerals (macro-minerals), which are abundant in the system, and trace elements (micro-minerals), which are present in extremely small quantities.

The essential macro-minerals are calcium, phosphorous, sodium, potassium, chloride, sulphur, magnesium and silicon.

The essential trace elements are iron, zinc, copper, iodine, manganese, chromium, molybdenum and selenium. (Vanadium, boron and tin are probably also essential).

 
 
 
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