Nutrients and a balanced diet

An ideal diet

Made up of foods which contain a balance of macro-nutrients and micro-nutrients: (of total calorie intake)

  2. FATS (30%)
  3. PROTEINS (10-15%)
  6. WATER


They are made up of sugars and are classified according to how many sugar units are combined in 1 molecule. Monosaccharides are the building blocks of carbohydrates.


Monosaccharides Disaccharides Polysaccharides
– Simple sugars –   When 2 simple sugars combine –   more than 10 sugar units, up to 1000s
–   Glucose, fructose, galactose (in fruits, veggies etc.) –  Sucrose (Table sugar)-  Lactose (in milk/dairy)-   Maltose (in malt) –  Starch (long chains of glucose, occurs as granules)-  Cellulose (major component of cell walls)-   Main components of dietary fibre

Main roles:

  • **Provide energy
  • The construction of the body organs and nerve cells
  • The definition of a person’s biological identity such as their blood group

How is it used?
Starches and sugars are the main energy-providing carbohydrate sources.
Simple sugars are absorbed directly by the small intestine into the bloodstream, where they are then transported to their place of use. Disaccharides are broken down by digestive enzymes into simple sugars. The body also needs the help of digestive enzymes to break down the long chains of starches into their constituent sugars which are then absorbed into the bloodstream.
The human body uses carbohydrates in the form of glucose.

Storage: Converted to glycogen, a polysaccharide similar to starch, which is stored in the liver and the muscles and is a readily available source of energy for the body.

Glucose may come directly from dietary carbohydrates or from glycogen stores.

As the brain needs to use glucose as an energy source, the level of glucose in the blood must be constantly maintained above at optimum level. Several hormones, including insulin, work rapidly to regulate the flow of glucose to and from the blood to keep it at a steady level.
Why important?

  • A diet containing an optimum level of carbohydrates may help prevent body fat accumulation;
  • Starch and sugars provide readily accessible fuel for physical performance;
  • Dietary fibre, which is a carbohydrate, helps keep the bowel functioning correctly.

As carbohydrates are found in a wide range of foods, they should be supplied from diverse food sources to ensure that the overall diet contains adequate nutrients. They also contribute to the taste, texture and appearance of foods and help to make the diet more varied and enjoyable.


90% of fats in the diet and body are in the form of triglycerides. Fatty acids and glycerol are the building blocks of fats.

Types of fatty acids

Saturated Monounsaturated Polyunsaturated
Definition no double bond in carbon atom chain One double bond Two or more double bonds
Characteristics (High proportion) –  relatively high melting temperature-  tend to be solid at room temperature

– usually liquid at room temperature

When oils are heated Most stable, most resistant to oxidisation More stable and can be re-used to a greater extent than polyunsaturated Less stable, cannot be re-used too often
Examples (Rich in) Dairy, meat, margarines, butter, lard, coconut/palm oil Nuts, olives, avocados, rapeseed and their oils Omega-3-  Fish (Salmon, mackerel, trout)-  Walnuts, soybean, flax seed and their oilsOmega-6

– Sunflower seeds, sesame, walnuts, soybean, corn and their oils

All fats are made up of a combination of all 3 fatty acids, but one type will generally predominate.

**Trans fatty acids –> Some frying and baking fats (e.g. hydrogenated vegetable oils) used in biscuits, cakes and pastries, dairy products, fatty meat from beef and sheep.

Role of fats

  • Main energy store in the body
  • The most concentrated source of energy in the diet
  • The body’s fat deposits are used to meet energy demands when dietary energy is limited, for example where people have a poor appetite or during starvation. They may also be needed when energy requirements are high such as during high levels of physical activity and for growing babies and children.
  • Fat deposits cushion, protect vital organs and help insulate the body
  • Carrier for vitamins A, D, E and K, and enables their absorption. They provide the essential fatty acids, linoleic acid (omega-6) and alpha-linolenic acid (omega-3).

Fats are also a major factor causing obesity as it has low satiety potential. But, obesity is also caused by lack of exercise. Thus only reducing fats in the diet is not sufficient for weight loss.
How it is used

Fat taken in the diet is digested in the small intestine with the aid of bile acids and salts which act as emulsifiers and break down the larger fat droplets into smaller ones.

  • Bile does not contain digestive enzymes!

These are then acted upon by “lipases” which are secreted in the intestinal digestive. juices. Ultimately the fats are converted into Fatty acids and Glycerol. These are then absorbed in the form of “chylomicrons (small packages of fat and protein)” into the lymphatic channels via the lacteals and poured into the blood. From here chylomicrons are taken to liver and converted into cholesterol and other forms of fats which are transported to other parts of the body in the form of VLDL, LDL, IDL and HDL.



Made up of amino acids linked together. A typical protein may contain 300 or more amino acids.

  • Each protein has its own specific number and sequence of amino acids.
  • The shape of the molecule is important as it often determines the function of the protein.

Amino acids

Essential Non-essential
indispensable amino acids that cannot be produced during metabolism by the body–> must be provided by our diet dispensable amino acids that can be produced endogenously in the body from other proteins

Importance of proteins

  1. Essential elements for growth (in children) and repair, ensuring all living cells perform their functions
  2. Control blood sugar levels — hormones (e.g. insulin)
  3. Digestion of foods — enzymes (e.g. amylases, lipases, proteases)
  4. Fight infections (antibodies), allow contraction (muscle proteins) etc.

How are they used? – protein cycle

Proteins in our body are constantly being built and disposed of. After we eat, proteins are broken down by digestion into amino acids. Amino acids are then absorbed and used to make other proteins in the body. Adequate protein and energy intake, on a daily basis ensures the cycle continues.
Where are they found?

  1. High biological value proteins –> Animal sources (e.g. meat, poultry, fish, eggs, milk, cheese and yogurt)
  2. Low biological value proteins –>  Plants (e.g. legumes, grains, nuts, seeds and vegetables)

Vitamins, minerals


  • generally help regulate body processes.


  • provide important growth and repair functions in bones and teeth (e.g. calcium, magnesium and phosphorus)
  • maintain the composition of body fluids (e.g. sodium, chloride and potassium)


Water is a solvent for numerous biochemical molecules giving solutions and enabling:

  • Transport of nutrients, e.g. glucose and amino acids in blood, and sucrose in phloem
  • Removal of excretory products, e.g. ammonia, urea
  • Secretion of substances, e.g. hormones, digestive juices.

– under construction –


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