Food and humans
Food substances
Food substances contain seven types of food substances that are essential to health
They are carbohydrates, lipids, proteins, minerals, vitamins, dietary fibre and water
Lipids are organic substances made up of carbon, hydrogen and oxygen atoms, but the H to O ratio is much greater than 2:1
Lipids are insoluble in water bud dissolve in organic solvents, ethanol
Triglycerides are the commonest type of lipids
They are formed from the condensation of three fatty acids molecules and one glycerol molecules
Glycerol
Lipids are stored in adipose tissues in our body
These tissues are found under the skin as subcutaneous fat, or around the internal organs
They act as energy reserves
They act as an insular to reduce heat loss
They act as a shock absorber to protect the internal organs
Phospholipids are a type of lipid
They are the major component of cell membranes
Lipids are involved in transporting and storing lipid-soluble vitamins (A and D) in our body
Lipids are involved in making some hormones
Proteins
Proteins are organic substances made up of carbon, hydrogen, oxygen and nitrogen atoms (sulphur)
Amino acids are the basic building blocks of proteins
An amino acid molecule has a carbon atom carrying an amino group, a carboxyl group, a hydrogen atom and a side chain
Different amino acids have different side chains
When two amino acids are joined together by condensation, a dipeptide is formed
This process is catalysed by enzymes in our body
Combination of a dipeptide with other amino acids forms a polypeptide
It coils and folds in specific ways due to the formation of chemical bonds between some amino acids on the polypeptide

Our body needs 20 types of amino acids to build up various proteins
Twelve of these amino acids can be produced by our body
They are known as non-essential amino acids