Nutrition - Peda.net
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Transcript Nutrition - Peda.net
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