Humans_Concept_1

Subject Facts

Food groups

There are various ways in which food can be categorised in terms of its nutritional value to us. However, they are categorised, any one food (such as potato crisps) will fall into more than one category A single piece of food may fit in to up to seven different nutritional categories:

Carbohydrates (eg starches and sugars) — used by the body to make energy.

Proteins (eg meat and cheese) — used by the body to manufacture and repair cells.

Fats — used to make energy and store it in the body. e Minerals (eg iron and calcium) — used in the manufacture of certain body parts, such as blood and bones.

Vitamins — essential (in tiny amounts) for the health of the body.

Water — the fluid in which all foods, once broken down, can be dissolved in order to be absorbed by the body..

Fibre — aids the movement of food along the digestive tract.

Of these essential nutrients, water is the most important. Without it, a human would not be able to survive more than a few days. Although each category is important for the growth and maintenance of a healthy body, it would be possible to survive for some time (though not very healthily) if certain elements were missing from the diet A protein-deficient diet, for example, will impair the body's ability to grow and repair damage. It is possible, depending on our level of activity, to survive for weeks or even months without food by consuming the food reserves that we carry around as fat and muscle. There are two elements to a balanced diet':

balancing energy input with energy usage (the more active you are, the more food you need),

an appropriate balance between the food groups to ensure healthy growth and development.

Carbohydrates

These are basically the materials that plants are made from as a result of the process of photosynthesis, which combines carbon (from carbon dioxide in the atmosphere) with water. Carbohydrates are sometimes called 'sugars' — but according to this word use, there are 'fast sugars' and 'slow sugars' (or simple and complex carbohydrates). The words 'fast' and 'slow' refer to the rate of release within our digestive system. 'Fast sugars' are easily digestible and can start to be used by the body as energy within minutes of eating, 'Slow sugars' (or starches) require more digestion, so their energy release takes much longer. It's like the difference between an explosion and a sustained fire: the total energy released may be the same, but the rate of release is very different.

The reason that 'fast sugars' release their energy so readily is that they are relatively simple in structure. Examples are glucose, sucrose (cane sugar), fructose (fruit sugar), lactose and maltose. Glucose, being a monosaccharide (single sugar molecule), is the easiest of the sugars to digest the others, including fructose, are disaccharides (double sugar molecules). When about 25 monosaccharides are linked together, a long-chain polysaccharide (starch) molecule is made. This is the chief means by which plants store energy, Animals use glycogen, a polysaccharide of about 1 0 molecules, to store their energy.

Plants also use a polysaccharide called cellulose for structural purposes: it provides the fibrous strengthening for plants. It is a very complex molecule, usually containing 200 to 300 monosaccharides. This complexity makes it all but impossible for humans to break down and use, though many animals can do so by means of a heavy-duty digestive system, often with a multichambered stomach. We can then eat these animals after they have turned the cellulose into meat.

Protein

The human body is about 50% protein (by dry weight), There are about 30,000 different proteins in our bodies, performing various different tasks — from muscle fibres to digestive enzymes and antibodies, Proteins are built up from amino acids, which are strands of carbon, oxygen, hydrogen and nitrogen atoms.

The range of tasks that they perform within the body makes them essential for growth, repair, general maintenance and the healthy functioning of the body.

Plants produce all the amino acids that they need as a result of photosynthesis and the absorption of nitrogen through their roots. Humans (and other animals) can synthesise many of the 20 or so main amino acids; but there are eight, known as the 'essential amino acids', that humans cannot make. These have to be obtained from food All of them can be found in plant seeds; but for two in particular (lysine and tryptophan), plants are not a very good source and can be supplemented by animal protein in the form of meat, eggs or dairy produce, It is recommended that babies receive 2.5g of protein for each kilogram of body weight per day. This is reduced to I and 0.8g per kilogram per day in children and adults respectively

There are basically two types of protein: fibrous and globular, Fibrous proteins are made of twisted long-chain molecules and have a great strength: they form much of our muscle and skin tissue. Globular proteins can be carried in the blood; they include digestive enzymes, hormones (such as insulin), pigments (such as haemoglobin) and antibodies,

Fats

Weight for weight, fat is the most energy-rich food that we can eat. It contains over twice as much energy per gram as either protein or carbohydrate. There are three forms of fat in our diet: monounsaturated (olive and peanut oil), polyunsaturated (sunflower and corn oil} from which margarine is made) and saturated fats (red meat, dairy produce). Where there is a high energy need, due to either a high level of physical activity or a cold environment in which energy is required to maintain metabolism (body heat), an increased intake of dietary fat may not cause any harm.

The key health link is between fat and cholesterol, Cholesterol is a fatty substance required by the body to protect nerve fbres, build cell walls and produce certain hormones — but the liver is quite capable of producing ail the cholesterol that the body requires, so we don't need to eat any extra. As fat doesn't dissolve in water, it requires special protein-based carriers (lipoproteins) to transport it around the body. Low-density lipoproteins (LDVs) take cholesterol out to the celi walls, and high-density lipoproteins (HDVs) scrape off the excess and return it to the liver for excretion via the digestive system.

Monounsaturated fats increase the proportion of LDVs, and the other fats increase the proportion of HDVs. If much more cholesterol is being taken out to the body than is required or can be brought back, then there is a build-up of cholesterol on the cell walls — particularly on the walls of veins and arteries. This build-up restricts the flow of blood through the vessels and increases the blood pressure (in order to get the same amount of blood through a smaller tube), putting a strain on the vessel walls and the heart — heart attack time! Intake of monounsaturated fats to produce more LDVs can, to a limited extent, counteract an excess of HDV-producing saturated fats,

In colder environments such as northern Canada and Scandinavia, where a high fat intake will quickly be converted into energy for maintaining metabolism, cholesterol is unlikely to be much of a problem. In Mediterranean Europe, fat intake has traditionally been confined to olive oil and moderate amounts of animal fat. With the warmer climate, far less energy is required to maintain metabolism (keep the body warm) In general, it is recommended that saturated fats should be avoided and polyunsaturated fats should not exceed 10% of the average energy intake. It is thought to be unsafe for fats (even monounsaturates) to exceed 30% of average energy intake.

Minerals

The body requires relatively small amounts of various metals to ensure the effective development and operation of particular parts of the body. But it won't do you much good to suck on a nail if you are anaemic (iron-deficient), as these minerals can only be absorbed as salts, Calcium, a mineral found in milk is a key component in the proper formation and repair of bones and teeth Common salt (sodium chloride) is necessary for the transmission of nerve impulses. No one food has all of the mineral salts that we require — hence the need for a varied and balanced diet (see below),

Vitamins

The human body, like that of any animal* relies on many interconnected chains of chemical reactions in order to function. Vitamins are chemicals that act as triggers for these reactions. The body only needs them in minute quantities; but if it is lacking in any one vitamin, whole chains of reactions can break down — which may lead to dangerous health problems. The table on below shows a range of the vitamins that we require for good health, together with their common sources and the potential effects of deficiency. Vitamins enable the body to convert other foods into more useful forms. They assist in cell formation, nerve transmission and the formation of DNA.

The two vitamin groups, fat-soluble and water-soluble, differ in terms of intake and storage. Fat-soluble vitamins can be stored within fatty tissues in the body. This means that their intake can be infrequent, as long as it is enough to ensure that the necessary quantities are available, Water-soluble vitamins, on the other hand, cannot be stored: any excess is excreted in the urine. intake of these vitamins thus has to be on a daily basis.

Some vitamins — particularly A, C, and E — help to counter the effects of potentially harmful chemicals known as free radicals These chemicals, produced as an effect of toxic substances such as tobacco smoke, damage cells and make them more susceptible to cancer-causing agents,

Fibre

Dietary fibre is necessary for the efficient working of the digestive processes. Although it cannot be digested by humans, it ensures that food keeps moving, At this point, the explanation becomes rather tasteless (no pun intended) but necessary for an understanding of why so many breakfast cereal manufacturers spend so much time advertising foodstuffs that humans can't actually digest,

As the chyme (the slurry-like mix of food and digestive juices) works its way through the ileum to the colon, it relies on peristalsis (successive contractions of muscular rings around the digestive tract) to keep it moving. If this slurry is very fluid or is full of slippery fat, the peristalsis will not be effective, and so the food will take longer to make the digestive journey. That may not be too bad in the ileum, though it will cause a bit of backing up' (indigestion), but later on distinct problems will occur. In the colon, the water in the chyme is reabsorbed into the body to avoid dehydration (this is why you must drink but not eat when you are suffering from diarrhoea), If the movement through the colon is slowed because the inner walls cannot 'grip' the chyme to move it forwardi then too much moisture will be extracted making the stools harden and leading to a difficult or painful bowel movement (constipation). The addition of fibre to the diet causes the chyme to have more of a bulk, to knit together more, so that the action of peristalsis is more effective, movement is more assured, liquid re-absorption is at a more appropriate level, and, well, there you go!

I'm not sure what it is, but children seem to find descriptions like that fascinating! Granted, an excess of dietary fibre can cause a few practical (and social) problems: speeding up the digestive process will make bowel movements more frequent, with an increased likelihood of gaseous bowel discharge — but this is still quite a small price to pay for a vastly reduced likelihood of colonic cancers.

Classifying foods

It is not really possible to place individual foods into one group or another, because most foods contain so many elements, However, it is possible to say that particular foods provide more of one element than another. A useful way of sorting foods is the 'three Gs".

'Go' foods are the ones that provide energy for movement and activity — carbohydrates and fats (and proteins).

'Grow' foods are the ones that you need for bodily growth and development — proteins (and vitamins and minerals),

'Glow' foods are the ones that you need for health and maintenance — minerals, vitamins and fibre.

What should we eat?

Identifying 'good' and 'bad' foods is not the issue here: it is the balance of food types that is important.

Carbohydrates, in complex forms such as such as bread, cereal, rice, potatoes and pasta, should provide all the energy requirements necessary in a slow release over the day. Sometimes there may be a need for a sugar boost' (headaches, shaking or feeling sick can indicate a drop in blood sugar level) between normal meal times, either just before or just after strenuous exercise. Eating food that requires a lot of digestion is not advisable just before exercise (it can lead to muscle cramps), so simple sugar foods are appropriate at this point; their energy value will be used almost immediately.

Protein sources such as beans, nuts fish, meat and dairy produce, will provide most of the 'building materials' that the body requires (as well as providing vitamins and minerals). Red meat and dairy produce, because of their saturated fat content should be eaten in moderation unless you are particularly active and likely to 'burn off' the energy value of the fat content.

Sources of vitamins and minerals, in particular fresh fruit and vegetables (which also have a considerable carbohydrate content) should be a regular part of any diet. Non-fresh or processed fruit and vegetables may have a reduced nutritional value; and over-cooking also reduces the useful food content.

Fats are not necessary as a specific component of a healthy diet. The small amount of monounsaturated fat (or oil) that you do require can be obtained from food such as nuts, dairy produce and some fruits and vegetables (such as olives). The fat in most processed foods is usually of the less useful polyunsaturated or saturated variety.

Fibre is contained in most basic foods, as long as they are not over-processed or over-cooked. Cereals and green vegetables are an excellent source of dietary fibre; but cereals may have been processed to have most of the fibre content removed (the bran is then often sold back to you in a separate packet!), and overboiling vegetables breaks down the structure of the cellulose (that's why boiled cabbage goes limp and floppy). Beware of processed snacks such as crisps: they may be based on the fibrous potato, but they have a fat content of up to 45%!

Malnutrition

Malnutrition is often perceived to be a problem caused by lack of food, but it is correctly defined as a deficiency or excess of one or more essential nutritional elements within a diet', Since the lack (or excess) of different nutritional elements will lead to different symptoms, it is impossible to say what somebody suffering from malnutrition will look like. Using the definition given above, most of the population of the world can be described as malnourished: they eat too much of some things and/or too little of others.

The food most commonly eaten in excess is fat. The average citizen of the USA will receive almost 40% of his or her daily energy intake in the form of simple processed sugars, 40% as fats and less than 20% as complex carbohydrates. Ideally, over 50% of energy intake should come from complex carbohydrates and jess than 10% from fats. in industrialised countries, there is also an increasing reliance on food supplements (vitamin and mineral tablets) to counteract a lack of fresh fruit and vegetables. Recent research has noted that the diet of British children was more balanced at the end of the 940s than it is now.

Starvation is an extreme form of malnutrition in which the body has suffered a deficiency of essential nutritional elements for a sustained period of time. When starvation begins, body fat is converted to provide energy; once this supply is exhausted, muscle tissue and internal organs begin to be converted and therefore shrink. More fluid is retained as internal systems begin to degenerate — this causes the distended stomach often associated with victims of starvation. The body loses its ability to repair itself and fight infection: illnesses such as respiratory infections and gastroenteritis, brought on by starvation, are the world's biggest killers of infants and young children.

Towards a balanced diet

The key to a healthily balanced diet is to consume a variety of food types. Neither chocolate nor lettuce will provide all that a growing child needs, but both have their value in the overall make-up of a diet Certain vitamins and minerals are essential, and most of these can be obtained by eating a range of fruit and vegetables, Protein can be obtained from a range of sources, but will not be eaten in isolation from other food types (fat in meat, carbohydrate in cereal). Clearly, an over-indulgence in simple sugars or fats will not be good; but over-eating within any food group will lead to problems.

In general, if your intake of energy (food) is greater than your use of energy (exercise), the excess will be stored as fat It is only when intake falls below usage that the fat will begin to be converted back into energy, Beyond this, starvation sets in as muscle tissue is converted into energy in order to maintain metabolism. The balance of energy intake and usage is a fine one to manage, and taking appropriate exercise is at least as important

Eating disorders

Obesity is a growing problem throughout the Western world It is caused as much by a sedentary lifestyle and poor dietary habits as by an increase in overall energy intake. The best solutions to this problem are education towards a reduced reliance on processed foods that contain high levels of simple sugars and fats, and increased acceptance, at a social level, of the need for exercise and physical activity.

The pressure of social norms and media-driven ideals of acceptable body shape has led to an increased frequency, mainly in young females, of cases of anorexia nervosa and bulimia nervosa, Although these are different conditions, both tend to result from the fear of becoming obese or the irrational need to reduce weight based on a poor self-image. There are a range of body shapes within the band of 'normality', the key aspect being that they are neither too fat nor too thin — both extremes are equally unhealthy.

Nutritional value

On all packaged foods, there will be a nutritional information panel which provides data concerning the energy, protein, carbohydrate, fat and fibre contents for a given amount of the food (usually either 100g or 100ml). In most cases the carbohydrates will be divided into sugar and starch. Sometimes the fat will be identified as either saturated or unsaturated. This allows comparisons to be made between the nutritional values of different foods. Where vitamins are included, the percentage of the recommended daily allowance (RDA) per portion or given amount of food will be stated too. Additionally, warnings are given for particular food allergies and intolerances (for example, nuts dairy, gluten).