1. State what is meant by the term balanced diet for humans

A balanced diet is a diet consisting of the right proportions of every type of nutrient (carbohydrates, proteins, fats, vitamins, minerals, etc.) in suitably sized portions.

A balanced diet should contain carbohydrate, fat, protein, fibre, vitamins, minerals and water. Note that fibre cannot be digested; it is used to form ‘roughage’ in the intestines, so the intestine walls have something to push against when moving the fool along the alimentary canal.

A balanced diet for different people is slightly different because our energy and nutrient requirements vary from person to person.


  1. List the principal sources of, and describe the dietary importance of:
    • Carbohydrates

Carbohydrates can be found in almost any food, but are present in large quantities in staple foods such as rice, potatoes, wheat, cereal, bread, etc.

They are our primary source of energy – they are broken down to release energy in respiration.

  • Fats

Fats are found in oil, butter, margarine, the white stuff on animal meat, etc.

Fats insulate the body, helping reduce fluctuations in our body temperature.

They are also a good store of energy – fats have a higher chemical potential energy per gram than carbohydrates, so they can store more energy in the same space. Often, excess carbohydrates are converted into fats for storage. When we don’t have enough carbohydrates for respiration, we can break down and respire fats, too.

  • Proteins

Proteins are found in meats, such as chicken, beef, fish, etc. It is also found in vegetables such as lentils and beans.

Proteins form our muscles, enzymes, skin, hair, etc.

  • Vitamins, limited to C and D

Vitamin C is found in many fresh fruits, especially citrus fruits, e.g. oranges, lemons, peppers, etc. It is also found in dark leafy greens.

Vitamin C is required for the development and maintenance of scar tissue, blood vessels and cartilage. It’s needed to make ATP (your source of energy), too. Vitamin C contributes to healthy teeth and gums as well.

Most of the vitamin D in our body is formed under our skin as a reaction to sunlight. Food sources include oily fish (e.g. salmon, sardines and mackerel), eggs, fortified fat spreads, fortified breakfast cereals, and some powdered milks.

Vitamin C is equally important to the maintenance of bone health as calcium because it regulates the flow of calcium into the bloodstream. This is done by promoting the absorption of calcium from food.

  • Mineral salts, limited to calcium and iron

Calcium is found in so many foods! Dairy foods such as milk, cheese and yoghurt contain it; greens like kale, broccoli and Chinese cabbage are good vegetable sources; fish with bones soft enough to eat, such as sardines and salmon; most grainy food, like bread or rice; etc.

Almost all calcium is stored in bones and teeth, where it supports their structure and hardness. Calcium is required for muscles to move and for nerves to carry messages between the brain and every body part. It’s also used to help blood vessels move blood through the body and to help release hormones and enzymes (almost every function in the body is regulated by hormones and enzymes).

Iron can be found in liver, meat, beans, nuts, dried fruit, whole grains (e.g. brown rice), fortified breakfast cereals, clams, oysters, shrimps and dark green leafy vegetables.

Iron is primarily needed to form the haemoglobin in RBCs. It also plays an essential role in the process of respiration (the actual complete process of respiration is much more complicated than the simple equation you have to learn about in IGCSE… not to worry, you can suffer through that in A levels :p)

  • Fibre (roughage)

There are two types of fibre: soluble and insoluble. In IGCSE, you should only have to learn about insoluble fibres. These fibres can not be digested. It basically adds bulk and ‘roughage’ to your food so that your intestines can push it along your alimentary canal. Insoluble fibre keeps your bowels healthy and helps prevent digestive problems.

Insoluble fibre sources include wholemeal bread, bran, cereals, nuts and seeds (other than golden linseeds).

  • Water

Water is usually present in varying amounts in food, but that’s not nearly enough for our body. Water can be drawn from wells, taken from springs, rivers, and other freshwater sources (salty seawater isn’t very good drinking water), but hopefully, you live in a house with running tap water.

Every cell in our body is made of and surrounded by water (unless they’re dead. Then maybe not.) – and as a whole, we are approximately 70% water. Every reaction in our body (respiration, digestion, growth, etc.) occurs in water. Hormones and other substances are dissolved in water; most of your blood is made of plasma (which is 92% water), gas exchange is possible because the gas exchange surface area moistened using water, etc. Basically, water, to us, is the ‘Elixir of Life’.


  1. Explain how age, gender and activity affect the dietary needs of humans including during pregnancy and while breast feeding

The amount of energy need is provided mainly by our carbohydrate and fat intake.

Growth in general also requires structures that are used for manufacturing cells like proteins, calcium, vitamin D, iron, etc.

In general, our energy demand increases until we stop growing (the bigger we are, the more of us there is to fuel).

While children are growing, they need more protein per kilogram of body weight than adults do. This means teenagers need more proteins and energy altogether than adults.

Generally, males use up more energy than females, too.

However, this varies significantly according to body type and activity – some body types have a higher metabolism, so they require more energy.

Pregnant females require a lot of protein, iron, vitamin D, calcium, too, because they are growing a foetus. However, women who are already eating a healthy diet do not need to increase their food intake when pregnant. Breastfeeding women need a lot of water. Note: breastfeeding women may also be referred to as lactating women. Lactating means producing milk.

People who lead a more active lifestyle or work manual labour jobs will require more energy – so they will have higher carbohydrate and fat requirements.


  1. Describe the effects of malnutrition in relation to starvation, constipation, coronary heart disease, obesity and scurvy

Malnutrition occurs when you don’t have a balanced diet. The definition I found online states that malnutrition is “lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.” (You don’t have to learn this definition!)

Starvation is caused by consuming too little food (maybe due to lack of food supply or a mental disorder causing an intense fear of gaining weight). This leads to acute weight loss, organ damage and in severe cases, death.

Constipation is when you are unable to defecate – which can be extremely painful. This is caused by a lack of fibre – your intestines won’t have anything to push on to move the food along the alimentary canal if there’s no fibre.

Coronary heart disease (CHD) is when cholesterol sticks to the walls of your arteries. Sometimes, this even forms blood clots. This cuts off or limits the supply of blood that your heart muscles receive, leading to a heart attack. This arises from consuming too many saturated fats.

Obesity arises from consuming too much food. This can lead to several diseases such as diabetes, strokes, difficulty breathing, etc.

Scurvy is a disease resulting from a lack of vitamin C (also known as ascorbic acid). It is very rare because it is pretty difficult to get scurvy – your diet has to be that bad. Early symptoms include weakness, feeling tired and sore arms and legs. Without treatment, you may have less red blood cells, gum disease, thinning hair, and bleeding from the skin. Since vitamin C is found in most fresh fruit and vegetables, especially citrus fruit like oranges and lemons, simply eat these fruit and vegetables to treat scurvy.


  1. Explain the causes and effects of vitamin D and iron deficiencies

One cause of vitamin D deficiency is a poor diet. If you don’t have enough vitamin D in your diet, you won’t ingest enough vitamin D. Lack of exposure to sunlight could also result in a vitamin D deficiency.

Vitamin D deficiency symptoms include bone pain and muscle weakness and rickets (a disease where the bone tissue doesn’t properly mineralize, leading to soft bones and skeletal deformities).

Iron deficiency could be due to a poor diet – you’re not eating enough iron-rich foods. Pregnant women need more iron than the rest of us, so are at a higher risk of iron deficiency. Inflammatory bowel disease can cause iron deficiency, and high blood loss through heavy periods or bleeding can also cause iron deficiency.

Iron deficiency is the leading cause of anaemia (a condition where there is a deficiency in RBCs or haemoglobin in the blood). As a result of the anaemia, and the iron deficiency itself, you may experience fatigue, decreased work and school performance, slow cognitive and social development in childhood, difficulty in regulating body temperature, decreased immune function and glossitis (an inflamed tongue).


  1. Explain the causes and effects of protein-energy malnutrition, e.g. kwashiorkor and marasmus

Protein-energy malnutrition (PEM) is a common childhood disorder. PEM is principally caused by lack of energy, protein and micronutrients, and is mostly seen in communities that have limited access to food. Drinking too much alcohol can also lead to PEM.

A child with PEM may be underweight, stunting (they have difficulty growing in height), wasting (unintended weight loss leading to weakness), kwashiorkor, and/or marasmus.


This occurs in people with severe protein deficiency. Kwashiorkor typically develops in children that are older than the children who develop marasmus. Having a mainly carbohydrate-based diet can lead to kwashiorkor.

Early Kwashiorkor symptoms include fatigue, irritability and lethargy. As the person continues to be deprived of protein, they may develop oedema (a puffy, swollen appearance due to fluid build-up in different parts of the body – there is often oedema in the legs of children with kwashiorkor), a bulging abdomen, an inability to grow or gain weight, and decreased immunity.


This occurs more commonly in young children and babies. It leads to dehydration and weight loss. Marasmus is a form of wasting. Marasmus symptoms include weight loss, stunting, dehydration, chronic diarrhoea, and stomach shrinkage.



Notes submitted by Sarah

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