Introduction to the nutrients

Nutrition

Blanced dietmaintains the homeostasis in the body by

supporting the metabolism in the cellsprovides the energy neededcontains fibre to aid the function of the gutthe components are:

carbohydrates, proteins, fats, vitamins, minerals, trace elements, dietary fibre (non-starch polysaccharide) and water

Balanced diet

Carbohydratesdietary carbohydrates originate mainly

from plantsmainly sugars and starchescomposed of carbon, oxygen and hydrogenare 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

Monosaccharidecarbohydrates have to be broken into

monosaccharides before they can be absorbed from the alimentary canal

highly soluble in waterthe simplest form of carbohydrate

glucosefructoselactose

Disaccharide

consists of two monosaccharides joined togethersucrose (table sugar) = glucose + fructoselactose (milk sugar) = glucose + galactosemaltose (malt sugar) = glucose + glucose

highly soluble in water

Polysaccharideconsists of numerous monosaccharides

joined togethermay be very large moleculespoorly 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 dietincludes cellulose from plantsimportant part of a healthy diet

The structure of carbohydrates

Main functions of carbohydrates

provide energy and heatusing carbohydrates saves proteins from

being used as a source of energyact as energy reserves

glycogen (liver and skeletal muscles)converted into fat and stored in fat depots

Dietary fibre

provides bulk to the dietslows the digestion ratestimulates peristalsisattracts water to faecesprevents constipationprevents some gastrointestinal disorders

Dietary fiber

Proteinsmade of amino acids joined together in

different combinationscomposed 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 acidsEssential amino acids (9 in number)cannot be synthesised in the body but

have to be included in the dietNon-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 kidneysthe rest will be converted to fat and stored in

the fat depots

Functions of proteins

growth and repair of body cells and tissuescarrier molecules (e.g. haemoglobin)synthesis of enzymes, plasma proteins,

antibodies, some hormonesproviding 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 fatsSaturated fatssolid at room temperatureoriginate from animal sourcesUnsaturated fatsfluid at room temperatureusually originate from vegetables or plantsEssential fatty acids3 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 fatsconcentrated source of energy and heatstorage of energysupport some organsstorage of fat-soluble vitamins (A, D, E, K)insulation, reduces heat loss through the

skinconstituent of myelin sheat of the nerve

cell formation of steroid hormones of

cholesterol