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Nutrition
Introduction to the nutrients
Blanced diet
 maintains the homeostasis in the body by supporting the
metabolism in the cells
 provides the energy needed
 contains fibre to aid the function of the gut
 the components are:
 carbohydrates, proteins, fats, vitamins, minerals, trace
elements, dietary fibre (non-starch polysaccharide) and water
Balanced diet
Carbohydrates
 dietary carbohydrates originate mainly from plants
 mainly sugars and starches
 composed of carbon, oxygen and hydrogen
 are classified according to the complexity of the molecules
from which they are formed
 glucose is the main form in which sugar is used by cells
Carbohydrates
Monosaccharide
 carbohydrates have to be broken into monosaccharides
before they can be absorbed from the alimentary canal
 highly soluble in water
 the simplest form of carbohydrate
 glucose
 fructose
 lactose
Disaccharide
 consists of two monosaccharides joined together
 sucrose (table sugar) = glucose + fructose
 lactose (milk sugar) = glucose + galactose
 maltose (malt sugar) = glucose + glucose
 highly soluble in water
Polysaccharide
 consists of numerous monosaccharides joined together
 may be very large molecules
 poorly soluble in water
 glycogen is made of numerous glucose units, a means of storing
glucose
 starch is equivalent storage polysaccharide (to glycogen) in
plants
Dietary fibre
 non-starch polysaccharide (NSP)
 indigestable part of the diet
 includes cellulose from plants
 important part of a healthy diet
The structure of carbohydrates
Main functions of carbohydrates
 provide energy and heat
 using carbohydrates saves proteins from being used as a
source of energy
 act as energy reserves
 glycogen (liver and skeletal muscles)
 converted into fat and stored in fat depots
Dietary fibre
 provides bulk to the diet
 slows the digestion rate
 stimulates peristalsis
 attracts water to faeces
 prevents constipation
 prevents some gastrointestinal disorders
Dietary fiber
Proteins
 made of amino acids joined together in different
combinations
 composed of carbon, hydrogen, oxygen and nitrogen, some
minerals can also be included
 20 amino acids are used as the principal building blocks of
protein
 may be in the form of animal or vegetable protein
Proteins
Amino acids
Essential amino acids (9 in number)
 cannot be synthesised in the body but have to be
included in the diet
Non-essential amino acids (13 in number)
 can be synthesised in the body (liver)
Most animal proteins have the full range of amino acids (=
complete proteins).
Vegetable proteins may lack adequate amounts of the
essential amino acids.
The structure
Excess protein
 If the intake of protein exceeds the need
 the nitrogen part will be converted to urea and excreted by the
kidneys
 the rest will be converted to fat and stored in the fat depots
Functions of proteins
 growth and repair of body cells and tissues
 carrier molecules (e.g. haemoglobin)
 synthesis of enzymes, plasma proteins, antibodies, some
hormones
 providing energy if needed
Fats
 belong to lipids together with phospholipids, fat-soluble
vitamins, cholesterol and prostaglandins
 composed of carbon, hydrogen and oxygen, but in a different
molecular structure from carbohydrates
 insoluble in water
Fats
Triglycerides
• consist of
one glycerol
and three
fatty acid
molecules
• make up
the majority
of all dietary
fats
The classification of fats
Saturated fats
 solid at room temperature
 originate from animal sources
Unsaturated fats
 fluid at room temperature
 usually originate from vegetables or plants
Essential fatty acids
 3 of the polyunsaturated fats are considered essential for
life (linoleic, linolenic, arachadonic acid)
Cholesterol
 a phospholipid
 a constiuent of the cell membrain and needed in the
production of steroid hormones
 can be synthesised by the body (liver)
 full-fat dairy products, egg yolk and fatty meat contain
cholesterol
Too much cholesterol
The functions of fats
 concentrated source of energy and heat
 storage of energy
 support some organs
 storage of fat-soluble vitamins (A, D, E, K)
 insulation, reduces heat loss through the skin
 constituent of myelin sheat of the nerve cell
 formation of steroid hormones of cholesterol