Human Nutrition, Nutrients and diet, summarized biology notes

 Learning Objectives

- describe the causes and effects of vitamin A, D, C and mineral salt (Iodine and iron only) deficiencies
- discuss the use of microorganisms in the food industry, with reference to yoghurt, bread and brewing
- describe the effects of malnutrition in relation to starvation, constipation, coronary heart disease, obesity and scurvy
- describe the role of a balanced diet for HIV-positive and people with AIDS
- discuss the problems that contribute to famine (unequal distribution of food, drought and flooding, increasing population)
- explain how age, gender and activity aftect the dietary needs of humans with reference to children, adults, nursing mothers, athletes and workers.

 Nutrients and diet
Nutrition means feeding. This is the process of taking in substances that our body needs to obtain energy and carry out the characteristics of a living organism, such as movement, growth and reproduction. Nutrition involves five processes: ingestion, digestion, absorption, assimilation and egestion of undigested food. The types of food that animals need are called nutrients. All animals, including humans, need seven types of nutrients. These are:
- carbohydrates
- proteins
- fats
- water
- vitamins
- inorganic ions or mineral salts
- fibre.

Vitamins
Vitamins are organic substances, as they contain a carbon element in their molecules, just like carbohydrates, fats and proteins. It is important to note that carbohydrates, fats and proteins are needed by your body in large amounts, but vitamins and minerals are required in minute (tiny) amounts. However, if any are missing completely, you can become very ill or you will suffer from deficiency diseases. Deficiency diseases are caused by a lack of certain nutrients in your diet. There are a number of vitamins that your body needs to stay healthy. At this level, you are only expected to know about vitamins A, C and D. You are going to learn about other types of vitamins when you continue with Biology at a more advanced level.
Vitamin A
Is essential for the repair and strengthening of epithelial tissues in the respiratory system. It also torms visual pigments in the retina of your eyes. The principle sources of vitamin A are foods such as butter, egg yolk, liver oil, milk and cheese. A lack of vitamin A in your diet can cause deficiency diseases like infection of the cells in the lining of the respiratory system and night blindness (poor vision at night).
 Vitamin C (ascorbic acid)
Is important for healing wounds, as well as keeping the skin and blood vessels healthy. It helps to form collagen, the protein in connective tissue that holds together the cells in tissues. You get it from food such as oranges, lemons, grapefruit, green vegetables and potatoes. Ihe lack of vitamin C in your diet causes a deficiency disease called scurw which causes pain in the joints and muscles and bleeding from the nose, gums and internal organs.
Vitamin D (calciferol)
Is needed to absorb calcium and phosphorus from food. You can find it in milk, egg yolks, liver and fish oils. Ultraviolet rays from the sun change lipids in your skin into vitamin D that is why it is called the 'sunshine vitamin'. If there is a lack of vitamin D in your diet, your body cannot absorb calcium. Calcium hardens bones. Children without enough vitamin D cannot absorb calcium, and will develop rickets.

Minerals
Mineral salts are inorganic elements (unlike vitamins, which are organic) and all originally come from the soil. Green plants are a direct and indirect source of minerals in food, since they absorb mineral salts from the soil. Your body needs about 21 different mineral salts, but in small amounts just like in the case of vitamins. Each mineral salt has its own function in your body. Lack of a certain mineral in your diet may lead to a deficiency disease. You need to know only two minerals at this stage, iodine and iron, apart from what you have learnt in the lower grades.
lodine
Your body needs iodine to make thyroxine, a hormone that controls the rate of metabolism in the body. Thyroxine is produced by the thyroid gland, situated in your neck just below the larynx. You get iodine from vegetables, seafood and processed table salt (added by manutacturers). A lack of iodine in your diet.causes the thyroid gland in the neck to swell up, because thyroxine cannot be produced. This swelling in the neck is called goitre Lack of thyroxine slows down the rate of metabolic reactions in the body.
 Iron
Iron is an essential part of haemoglobin, which is a pigment in red blood.cells. Haemoglobin is responsible for carrying oxygen around the body. Red meat, particularly liver and kidney, eggs, peanuts and green vegetables, such as spinach, are all principle sources of iron. A lack of iron in the diet means that there is less haemoglobin in the blood, therefore less oxygen gets to the cells and less energy is released as a result. This condition is called anaemia, A person suffering from anaemia looks pale, becomes tired easily, feels breathless and is often depressed.

 Use of microorganisms in the food industry
For thousands of years, people have eaten foods that have been made using microorganisms, although it is only in the last one hundred years that people have understood what they were doing! Have you ever made yoghurt or bread?
 Yoghurt
Yoghurt is made from milk by the action of lactate-producing bacteria. This bacterium is perfectly harmless to humans. These bacteria are commonly found in yoghurt starter cultures. They are added to milk in approximately equal proportions. Most commercial producers pasteurise the milk at 90 °C for 20 minutes. The mixture is incubated at around 45 °C for 5 hours, during which time the bacteria break down milk proteins into peptides. The fermentation produces lactate, which brings the pH down to 4.

Fermentation by-products, including ethanol and methanoic acid, give yoghurt its characteristic flavour. The product is cooled to prevent further fermentation. Sometimes fruit pulp, colouring and flavours are added before packaging. Some yoghurt is heat-treated before or atter packaging to kill any bacteria, but most contain live bacteria.
 Bread
Bread is made from tlour, yeast, sugar and water. The yeast in the presence of sugar and water begins to produce enzymes. that break down the starch in the tlour to make sugars. The yeast then carries out respiration, using the sugars asa source of energy. The carbon dioxide gas given off in respiration makes the sticky dough rise. Gluten, a protein in flour, holds the bread together as it cooks and gives it lightness.
 Brewing
Beer is made from four basic ingredients: barley, water, hops and yeast. In order to make beer, barley seeds are allowed to germinate by soaking the barley seeds in warm water. This is called malting. The germinating barley seeds break down their carbohydrate stores, releasing sugar, After a couple of days, the barley seeds are gently roasted (which kills them) and put into a fermenter with yeast. The yeast uses the sugar for anaerobic respiration and produces beer. You need to know an experiment that shows the production of CO₂ by yeast, in different conditions. The best example is to mix a yeast suspension with a sucrose solution and place it in a boiling tube with a delivery tube attached. Any CO₂ produced can be collected over water or bubbled through limewater.

Malnutrition and starvation
Starvation is when people do not have enough food of any kind. On the other hand, malnutrition refers to a lack of or an excess in particular areas of the diet. One type of malnutrition, called kwashiorkor, is due to a lack of protein. This results in wasting of the limbs, puffiness and a pot-belly. It occurs mainly in children.

Diet and heart disease
People who eat a lot of saturated fat and cholesterol in food are much more likely to get coronary heart disease than people who eat a balanced diet. Coronary heart disease occurs when the coronary arteries that lead to the heart begin to narrow. Narrowing typically results from plaque deposits in the arteries, causing a reduction in the amount of oxygen-rich blood that can reach the heart, leading to a heart attack. Examples of food containing saturated fat are milk, cream, butter, cheese, red meat and eggs. Vegetable oils, such as suntlower oil, Contain unsaturated fats. Fish and white meat, such as chicken, do not cause heart disease.

Constipation

If a person eats large quantities of processed food, it makes the faeces hard and difficult to push out of the anus. Constipation can be prevented by eating lots.of fibre, found in vegetables and fruit. This will also help reduce the risk of cancer of the large intestine.

 Obesity
Excess carbohydrates in the body are changed into fat in the body. Excess fat can cause a person to become obese when the fat is not used up by the body.

 Scurvy
An insufficient amount of vitamin C in the diet leads to scurvy. Early stage symptoms are weakness, feeling tired, sore arms and legs. If treatment does not take place, decreased red blood cells, gum disease, changes to hair, and bleeding trom the skin may occur. As scurvy worsens, there can be poor wound healing, personality changes, and finally death from infection or bleeding. Scurvy occurs most commonly in people with mental disorders, unusual eating habits, alcoholism, and old people who live alone. Scurvy is treated with vitamin C supplements taken by mouth Vitamin C is found in citrus fruits and a number of vegetables, such as tomatoes and potatoes. Cooking often decreases vitamin C in foods.

 Nutrition for HIV-positive people and AIDS sufferers
It is very important for people who are HIV positive to eat a balanced diet. They should be encouraged to eat nutritious food, especially vitamin-rich food. Food will not, of course destroy the HIV, but it can help the body to remain healthy and strengthen the body's immune system, which is attacked by the virus. Severe weight loss is a common problem for AIDS sufferers. This can be due to:
- a lack of nutritious food
- poverty
- difficulty in swallowing (caused by thrush and or sores in the mouth and oesophagus)
- a loss of appetite and nausea
- severe vomiting
- severe diarrhoea
- a loss of appetite due to depression.
AIDS Sufferers should be encouraged to eat high-protein food that stimulates weight gain by building up the muscles. This includes food such as meat, chicken, fish, yoghurt, beans, nuts, and dairy products. Vitamins and minerals are needed to help the immune sytem fight infectious diseases. These can be obtained from fruit and vegetables, such as oranges, carrots, pumpkin and spinach. Carbohydrates are necessary to provide energy. They are found in cereal products, such as rice, mahangu, macaroni and brown bread. Fats are also needed as a source of energy and to build up energy reserves, therefore AIDS sufferers are encouraged to eat foods such as butter, full-cream milk, nuts and seeds.

 World food supplies
There are many parts of Africa where not enough food is grown to feed all the people who live there. Sometimes this leads to starvation. You have probably seen photographs or television programmes about people suffering from famine in different parts of the world. In many of these places, however, the government is able to buy and import food from other countries. If the government cannot afford to do this, then food may be donated by other countries.

Starvation and malnutrition
In many countries in the world, there is no danger of people suffering from obesity. In northern Africa, for example, several years of drought have meant that the harvests have not provided enough food for all the people. Despite help from Europe, the USA and Russia, many people have died of starvation. Even if there is enough food to keep people alive, they may suffer from malnutrition. Malnutrition is caused by not eating a balanced diet, One common form of malnutrition is kwashiorkor. This is caused by a lack of protein in the diet. This is most common in children between the ages of 9 months and 2 years, after they have stopped feeding on breast milk. Kwashiorkor is often caused by poverty, because the child's mother does not have enough high-protein food to give the child. It could also be caused by a lack of knowledge about the right kinds of food that should be eaten. Children suffering from kwashiorkor are always underweight for their age. They may often look quite fat, though, because their diet may contain a lot of carbohydrates. If they are fed a high-protein diet, they usually begin to grow normally again. Kwashiorkor means 'the deposed one'. It describes the child who is taken off or 'deposed' from his or her mother's breast to make way for the newborn baby. The older child is weaned off his or her mother's milk and usually given a staple diet of starchy food. Although the child may get enough energy, starchy foods are relatively low in protein. The proteins that are present in the food usually lack some of the essential amino acids. Maize, the staple food in southern Africa, lacks two essential amino acids, which explains why kwashiorkor is Common in the region. Peanuts are a good source of the two amino acids missing from maize; peanuts or peanut butter in the diet can help to prevent the disease. Marasmus is a form of severe malnutrition, characterised by energy deficiency. A child Suffering from marasmus is starving. The child does not get sufficient food for energy or for growth. The body breaks down its own structural proteins like muscles to provide energy, and the body wastes away. The difference between marasmus and kwashiorkor is that kwashiorkor is a protein deficiency with adequate energy intake, whereas marasmus is an inadequate energy intake in all forms, including protein. Many people eat too many carbohydrates. This is partly because carbohydrates are cheaper than protein, and partly because they are satistying foods; in other words, they make you feel full. The staple foods of many countries are foods rich in carbohydrates, for example rice, which is the staple food of China, maize in South Africa, and potatoes for much of Europe. It is tragic that, even with the present world population level, there is not enough everyone. The problem is the distribution of food. The distribution of food relies being able to buy food, and being able to transport food while it is fresh.

There are several reasons for the unequal distribution of food in the world. Some of the current reasons include:
 Increasing population:
When the population.increases, the availability of food resources fall, due to the inability to grow sufticient food, and not enough money to buy more, for example, in China and the Far East.
Urbanisation:
As more and more people move toward cities, there are fewer people available to grow crops and produce food. This reduces the availability of food, and increases the price of food, for example, in South America.
Drought and flooding:
These opposites have a major effect on food availability. In Africa, droughts are responsible for many food shortages, and in Asia, floods are the main cause of food shortages. The lack of rain or unpredictable rainfall means that crops cannot be planted, or they fail to grow.
War refugee movement:
This is a major problem in certain parts of Africa, particularly DRC, Ethiopia, North and South Sudan, Burundi and Rwanda. During war, people are unable to grow food they usualy move away from areas where the war is taking place. The land is left uncultivated and the people become refugees.
Disease:
Diseases such as tuberculosis, malaria and AIDS affect the working adult population. As a result of widespread epidemics, people are unable to cultivate the land and grow their own food.

As a result of these problems, the traditional way of life changes or breaks down. People lose the ability to feed themselves through subsistence farming. Lack of food leads to low resistance to disease, and can lead to starvation and death. In Namibia, most farmed foods are carbohydrate foods. Mahangu and millet in the north, maize in the Caprivi and Tsumeb-Otavi-Grootfontein triangle, and grapefruit at Noordoewer in the south are all largely carbohydrate foods.

 How much should you eat each day?
The amount of food that you need depends on how much energy you use in a day. The more energy you use each day, the more energy you need in your diet. At different stages in your life, you need different proportions of the seven types of nutrients in your diet. The amounts and proportions of the different foods you need in your diet depend on:
Your age:
When you are a child, you need plenty of proteins for making new cells In during growth. Teenagers need more energy than babies because they are larger, and more active.
Your work (activities):
When you are doing sport (athletics) at school, you need proteins for building muscles and plenty of carbohydrates for energy. If you are playing soccer, for instance, you need more proteins and carbohydrates than someone who is playing snooker. If you are doing heavy work, you need more carbohydrates than someone who is doing light work, for example, a mineworker needs more energy than someone who is working in an office.
 Your sex:
Males use more energy than females of the same age, even if they are doing the same work. This is because they have more muscle mass and are generally larger.
Your state of being:
If you are pregnant, you need more iron to build the fetus's blood, and vitamin C and calcium to build the fetus's bones. A woman who is breast feeding needs more energy to satisty her body's needs, as well as produce milk for her baby's needs.
 Recommended daily allowance (RDA):
An average person needs to take in the following in his or her daily diet:
- 12000 kJ energy-yielding nutrients
- 54 g protein
- 500 mg calcium
- 12 mg iron
- vitamins.

The end, posted by Miss Fang Xiu.