Site author Richard Steane
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The Components of Human Diet

Main classes of food - Background Information
Name of Class Chemical Elements
(and proportions)
broken down into/
built up from:
Function in organism
and in cell


{sugars - soluble

{polysaccharides - insoluble
(1:2:1 approx)
"simple" sugars
e.g. glucose C6H12O6
sucrose C12H22O11
***main substrates used in respiration***
sugars - fuels for instant use

polysaccharides are mainly energy stores
{glycogen (liver, muscle of animals)
{starch (found in plants only)
cellulose - plant cell wall - difficult to break down


- do not mix with water
(i.e separate out when shaken together)
C H O (1:2:less) fatty acids and glycerol fuel & long-term high energy storage
**cell membranes**


C H O & N
sometimes S, P
(20 types)
body building
**part of cytoplasm** - only respired as last resort
***All enzymes are proteins***

Like other animals, humans need food for several reasons, i.e. to perform a variety of functions in the body, and accordingly we need different amounts of these components.
Complete the table below to summarise the contribution made by each component, and the amount required for a healthy diet:
(use ++, +, -)
amount required by adult
per day (RDA)

(1 g=1,000 mg=1,000,000 µg)
CLASS OF FOOD for growth and repair for energy to stay healthy
FATS and OILS + ++ - 50-100g
PROTEINS ++ - + 80-100g
VITAMINS + + + A: 300-1200 µg C: 20--60 mg
MINERALS (IONS) + - + a few grams
FIBRE - - + 30 g
WATER + - + .

You are what you eat!

Which part of the human cell consists mainly of fats and protein?

? > cell (& other internal) membranes

Which part of the human cell consists mainly of water & protein?

? > cytoplasm

Which part of the human cell consists mainly of nucleic acids and proteins?

? > nucleus
Which components of diet are said to be "body building"?

> protein (and minerals)

Which part of the PLANT cell consists mainly of "fibre"?

? > cell wall

Diet and energy supply

What is the name of the process by which we get energy from food?
? > respiration

Name two units in which the energy content of food is measured, and give the conversion factor between them.

> Calories = > 4.2 kilojoules (kJ)

What processes can food energy be used for? (clue: there are 7 of them, including getting food, and extracting energy!)

? > feeding >respiration >movement > growth

> excretion > sensitivity > reproduction

We all need different amounts of energy, and consequently different amounts of food (or at least, energy-providing foods!).

What factors may affect our energy requirements?

>age > sex > lifestyle/occupation

What are the likely long-term consequences of eating

1) too much food > fatness/obesity 2) not enough food? > loss of weight

NOT Anorexia - a nervous condition: anxiety over slimming etc
A balanced diet is not just one providing enough energy. It must also provide the right amounts of the major and minor dietary components. No single food contains these in entirely correct proportions. For this reason, it is a good idea to eat a variety of different foods.

11000kJ per day may now be seen as an excess. It all depends how active you are!
Many food manufacturers provide information about the nutritional content of their products.
It would be interesting to see what dietary components would be in excess, and what would be deficient, if all the energy you require (say 11000 kJ per day) was provided by one food.
Do some research at home, perhaps starting with your favourite food.
By scaling it up, work out the amount you would have to eat in order to give you 11000kJ, then the amounts of the major dietary components this would include. Add ++ , + or - to show if this is more than, or less than, the recommended daily amount of each.

Examples of food types
Baked Beans Example 2. Example 3.
Total amount required to give 11,000 kJ 10 (450 g) cans! . .
FATS and OILS 20g - . .
PROTEINS 216g ++ . .
Any other contributions? fibre 310g ++++! . .
water 3.14 litres . .
Another home activity: Collect food labels for next week.

Give some examples of foods which are especially rich in these components:

Carbohydrates Proteins Fats
> sugar/fruits
> starch - rice/potatoes/pasta/bread
> meat/fish
> peas & beans
> butter,
What condition is caused by a lack of protein in the diet?

> kwashiorkor/marasmus

Minor Components of diet

Vitamins and minerals can be said to be minor components of diet because smaller quantities are required by the body, and these are likely to be obtained from the same sources as the major components: proteins,carbohydrates, fats and oils. They are, however, essential for life, because they have special chemical functions in the body. Incidentally, they do not need to be digested into smaller sub-units before they are absorbed into the body.

If not enough of each are available, then "deficiency diseases" can result. Nevertheless, none of these components is likely to be lacking in a sensible modern western diet, but they may have great effects in poor and under-developed countries.

How do vitamins and minerals differ chemically? (Don't get too technical!)

Vitamins are > complex organic compounds (many C-C [carbon to carbon] bonds)

whereas minerals are > simpler inorganic substances, salts, ions
Try to find out how many vitamins are considered essential for the human body, and give their (code) names. > A, B (several, e.g. B1, B6, B12), C, D, E, K
Fill in the table below with information about the main ones.

Vitamin Source Importance for health Lack causes Notes
vitamin C
(ascorbic acid)
fruits, green vegetables healthy skin & gums scurvy added to food to stop fats "going off"
vitamin D
(also called calciferol)
cod liver oil helps body absorb calcium for bones etc rickets
(see also calcium)
also made in skin by action of UV light
........ ........ ........ ........ ........

Vitamins are sometimes divided into 2 main groups. What is the basis of the division, and which ones are in each of the groups?

>Vitamins A,D,(K) soluble in fat > Vitamins B,C soluble in water

Similarly, list some details about minerals needed by the body:

Mineral Element Source Importance for health Lack causes Notes( incl RDA?)
Calcium milk, eggs strong bones & teeth rickets .......
Iron liver part of haemoglobin - in red blood cells anaemia .......

Fibre, or Roughage

On the other hand, fibre is notably missing from modern processed food, and a feature of diet in less-developed countries. It is thought that a "western diet" containing much "processed foods" brings with it increased risk of a number of diseases and conditions, ranging in severity from bowel cancer to constipation. The risk can thus be reduced if the proportion of foods containing fibre is increased.

Fill this in as before.

bowelcanceruk (4K)

Good source of fibre Importance for health Notes
brown rice gives gut muscles something to act on processed out of modern food
brown bread gives gut muscles something to act on
? ? ?
Give two reasons why you should "eat your greens".

> They contain minerals, e.g. Fe

>They contain fibre

>"Mum says so"!

Give two reasons why sugar may be bad for you. Qualify your statements.

> (in presence of bacteria) cause tooth decay

> (eaten in excess) can cause you to get fat

Is brown sugar any better? Explain why.

> No > Brown colour is not the same as fibre

Are potatoes necessarily bad for you? Explain as fully as you can.

> No > skin has protein, fibre, vitamin C high water content - only 20% starch

" Potatoes are good for us becase they give us energy in the satisfying form of starch "

How good a food is milk? Find out what dietary components it does and does not provide.

Fill in the two sides of this chart.

Milk contains Milk does not contain
protein fibre
carbohydrate - sugar: lactose some vitamins
(good energy source, especially for babies!),
and fat soluble vitamins A & D
minerals, e.g. calcium (good for bones & teeth) ?
Similarly, use this chart to show what dietary components a wholly vegetarian diet does and does not provide.
Vegetarian diet is HIGH in: Vegetarian diet is LOW in:
fibre some vitamins
carbohydrates possibly proteins
? ?

This topic has connections with other BioTopics units :-

Healthy diet calculator
Vitamins and Minerals
Food spoilage and additives
Experiment to show some methods of preserving food
Dietary recommendatioms

Nutritionists can help decide which type of diet works best for any individual. Some diet plans like Reverse Health reviews use an app to personalize their program and track progress.

Return to the previous unit? Return to the contents page? Another look? Back to the BioTopics index page? Next Unit?
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