Epidemiological research is the
study of disease trend among populations. It can involve comparison between
inhabitants of different countries, or of those living in the same country,
state and city. Such populations based research can be useful in identifying
potentially fruitful leads for further research. (Biss et al, 1971)
The masai people are a war-like tribe residing in East Africa who for the last 10,000 years have existed as cattle herding nomads. Their sustenance is derived from large amount of high fat milk and meat which may be supplemented by fresh cattle blood in the dry season.
Thanks to their copious consumption of high fat animal food, the masai males ingests a hefty 300g of mostly saturated fat on a daily basis. If lipid hypothesis had any merit, the masai resident should be riddled with obesity and coronary heart disease (Biss et al. 1971).
The residents of Pukapuka and Tokeluau, two tiny pacific atolls, were also examined in 1960’s. Due to their daily consumption of coconut, the Pukapuka and Tokeluau obtained 35%-53% of their calories from fat respectively. Only a few grams of their daily fat intake were in the form of unsaturated fat, the rest were saturated. Despite their high consumption of saturated fat, residents of both island enjoyed a complete absence of chronic heart disease and a remarkable low incidence of other degenerative diseases (Prior et al, 1981).
The more fashionable current dietary theories is that of the “Mediterranean diet” which attributes the low rate of coronary heart disease (CHD) in southern Europe to the frequent intake of olive oil, fruits, vegetable, legumes and a supposedly low level of saturated fat consumption (FAO Data, 1961- 1999). There is no arguing the benefits of fruits and vegetables. France enjoys the lowest incidence of coronary heart disease in south Europe while enjoying the highest saturated fat intake (FAO data, 1961-1999). Red wine intake has been posited as an explanation for this alleged “paradox” but does not satisfactorily explain the difference. After all, the per capita wine consumption of the Italian, fond of their “Vino rosso” is virtually identical to that of the French yet they suffer from a notably higher rate of coronary heart disease CHD) (FAO data, 1961-1999).
The masai people are a war-like tribe residing in East Africa who for the last 10,000 years have existed as cattle herding nomads. Their sustenance is derived from large amount of high fat milk and meat which may be supplemented by fresh cattle blood in the dry season.
Thanks to their copious consumption of high fat animal food, the masai males ingests a hefty 300g of mostly saturated fat on a daily basis. If lipid hypothesis had any merit, the masai resident should be riddled with obesity and coronary heart disease (Biss et al. 1971).
The residents of Pukapuka and Tokeluau, two tiny pacific atolls, were also examined in 1960’s. Due to their daily consumption of coconut, the Pukapuka and Tokeluau obtained 35%-53% of their calories from fat respectively. Only a few grams of their daily fat intake were in the form of unsaturated fat, the rest were saturated. Despite their high consumption of saturated fat, residents of both island enjoyed a complete absence of chronic heart disease and a remarkable low incidence of other degenerative diseases (Prior et al, 1981).
The more fashionable current dietary theories is that of the “Mediterranean diet” which attributes the low rate of coronary heart disease (CHD) in southern Europe to the frequent intake of olive oil, fruits, vegetable, legumes and a supposedly low level of saturated fat consumption (FAO Data, 1961- 1999). There is no arguing the benefits of fruits and vegetables. France enjoys the lowest incidence of coronary heart disease in south Europe while enjoying the highest saturated fat intake (FAO data, 1961-1999). Red wine intake has been posited as an explanation for this alleged “paradox” but does not satisfactorily explain the difference. After all, the per capita wine consumption of the Italian, fond of their “Vino rosso” is virtually identical to that of the French yet they suffer from a notably higher rate of coronary heart disease CHD) (FAO data, 1961-1999).
BIO-AVAILABILITY
OF NUTRIENTS
The bioavailability of food consumed is an important
issue in nutrition. Nutrition is the relationship of food to the health of the
human body (Whitney et al, 1993,
Trayor, 1996). The food we consume should provide our bodies with the nutrients
(carbohydrate, protein, lipids, minerals, vitamin and water) necessary for good
health (Whitney et al. 1993, Trayor
1996).
Bioavailability is the technical
term used to convey the fact that you do not absorb 100% of all nutrients
consumed, no matter what form the nutrient is taken (Brooner, 1993). A number
of factors affects bioavailability of nutrients.
1) Factors contained on the food itself.
2) Factors of human physiology
3) Factors specific to your health status.
4) Factors related to the food processing.
5) Presence of anti-nutritional factors
(Dreosti 1993).
NUTRITION
Nutrition
is the provision to the cells and organisms the materials necessary (inform of
food) to support life. (Ezeilo, 2002). The purpose of good nutrition is to
provide energy, promote growth and repair of tissues and to regulate various
process in the body. The essential nutrients comes from carbohydrate, lipids,
protein, minerals, vitamins and water (Ezeilo, 2002).
CLASSES
OF NUTRIENTS
There
are 6 major classes of nutrients; carbohydrate, fats, proteins, minerals,
vitamins and water. These nutrient classes can be categorized as either macro
nutrients and micro-nutrients. The macro nutrients provides structural
materials (amino acids from which proteins are built and lipids from which cell
membranes and some signaling molecules are built) and energy (Shils et al. 2005). Some structural materials
can be used to generate energy internally, and in either case it is measured in
joules or kilo calories (Shils et al.
2005).
Carbohydrate and protein provides
17kJ approximately (4Kcal) of energy per gram (Shils et al. 2005); though the net energy depend on such factors as
absorption and digestive effort (Shils et
al; 2005).
CARBOHYDRATE
Sugar
and starch are important carbohydrate in our diet. Starch is abundant in yam,
cassava, potatoes, bread, maize, rice and other cereals. Sugar appear in our
diet mainly as sucrose (table sugar) which is added to drinks and many prepared
foods such as biscuits and cakes ( Ramlingam, 2001).
Although all foods provide us with
energy, carbohydrates are the cheapest and most readily available source of
energy. They contain the elements carbons hydrogen and oxygen (eg. Glucose C6H12O6).
When carbohydrates are oxidized to provide energy by respiration, they are
broken down to carbon dioxide and water. One gram of carbohydrate can provide
an average of 16KJ of energy (Ramlingam, 2001 and Shils et al 2005).
Excess carbohydrate in the body is
converted to glycogen or fats in the liver, the glucose is stored in the liver
and muscles while the fat is stored as fat depots around the kidney or under
the skin (Ramlingam, 2001).
Carbohydrates
are of 3 classes
1) Monosaccharide
2) Diasaccharides
3) Polysaccharides
Monosaccharide
are the building blocks for all carbohydrate and are of two types, the 6 carbon
type (Hexose) namely glucose, fructose and galactose and the 5 carbon chain
type (Pentose) namely ribose and xylose. Diasaccharides found in food are
sucrose, lactose and maltose. Polysaccharides found in food include starch and
fibre (Ezeilo, 2002).
SOURCE OF CARBOHYDRATES
Quantitatively,
most dietary carbohydrates come from plants, and about 50% are starches. Some
monosaccharide are derived from the digestion of milk (eg galactose) or the
metabolism of glucose (eg Ribose) in the body. The glycogen in meat (liver and
muscle) is converted into lactic acid during slaughter of the animal. The
common source and functions of the various carbohydrates are given in the table
below (Ezeilo, 2002)
Common source of Dietary carbohydrates.
Monosaccharide Glucose
|
Fruits,
vegetable and honey
|
Fuctose
|
Fruits
and honey
|
Galactose
|
Digestion
of milk lactose
|
Disaccharides Lactose
|
Milk
|
Maltose
|
Germinating
seeds.
|
Sucrose
|
Sugar
cane, pineapple, carrot
|
Polysaccharides fibre
soluble
|
Fruits,
legumes and grains
|
Insoluble:
|
Vegetable,
wheat and bran.
|
(Ezeilo,
2002)
FUNCTIONS OF CARBOHYDRATES
1) Source of Energy: Carbohydrate in the
form of sugar or starch supply energy to non-photosynthetic organism.
2) Storage of Energy: Carbohydrates can be
stored in the form of starch and glucose in plants and animals respectively.
3) Structural Component: Carbohydrate Polymers
serve as structural elements in cell walls of bacteria, connective tissues and
cell coats of animals.
4) Lubrication:
Carbohydrates Lubricates skeletal Joints to provide adhesion between cells.
Hybrid molecules such as proteoglycans and glycoprotein are components of cell
surface and intracellular supportive systems (Diribe et al, 2002).
BIOMEDICAL IMPORTANCE OF CARBOHYDRATE
1) Sorbitol,
a sugar alcohol obtained from glucose produces cataract when it accumulates in
the lenses of diabetics.
2) Mannito,
also a sugar alcohol is used as osmotic diuretic to reduce cerebral edema.
3) Keratin
sulphate when found along with chrondrotin sulphate in the cartilages, the
cornea of the eye and pulpy nucleus of the intervertebral disc may result to
disease conditions.
4) Hyaluronate is an effective lubricants
and a shock absorber.
5) Heparin
is found in the mast cell and can be used as an anticoagulant to inhibit blood
clothing (Diribe et al, 2002).
PROTEINS
Proteins
are built from amino acids, unlike, carbohydrates and fats which are made up of
carbon, hydrogen and oxygen. Amino acids have in addition nitrogen and some of
them also contain sulphur (Ezeilo, 2002).
Proteins when digested provide the
chemical substance needed to build cells and tissue e.g. skin, muscle, blood
and bones. Neither carbohydrates, nor fats can do this and so it is essential
to include some proteins in the diet (Ramlingam, 2001).
The
body requires amino acids to produce new proteins (Protein retentions) and to
replace damaged proteins (maintenance) as there is no protein or amino acid
storage provision, amino acid must be present in the diet. Excess amino acids
are discarded, typically in the urine (Ezeilo, 2002).
Some amino acids are essential (an
animal cannot produce them internally) and some are non-essential (the animal
body can produce them from either nitrogen-containing compound). About 20 amino
acids are found in the human body, and about ten of these are essential and
therefore must be included in the diets (Berg et al 2002). A diet that contains adequate amount of amino acids
(essential) is particularly important in some situations during early
development and maturation, pregnancy, lactation or injury (Berg et al, 2002). Excess amino acids from
protein can be converted into glucose and used for fuel, a process called
gluconeogenesis. The amino acids remaining after such conversions are discarded
(Berg et al, 2002).
SOURCES OF PROTEIN
A
complete protein sources contain all the essential amino acids, an incomplete
protein source lacks one or more of the essential amino acids. It is possible
to combine two incomplete protein source (eg. Rice and beans) to make a
complete protein source and this characteristic combination are the basis of
distinct cultural cooking tradition. (Ramlingan, 2001).
Sources of animal protein include,
Meats, fish, egg, diary products such as milk and cheese (Ramlingan, 2001).
Plant contains some protein, but groundnuts and beans or cereals like wheat and
maize are the best source of plant protein ( Ramlingan, 2001).
CLASSES OF PROTEIN
1) Fibrous
Protein: Have a relatively simple, regular linear structure. These proteins
often serve structural roles in cells. They are insoluble in water or in dilute
salt solution ( Garrette et al, 2005).
2) Globular
Protein: Are roughly spherical in shape, their polypeptide chain is completely
folded so that the hydrophobic amino acid side chain are in the interior of the
molecule and the hydrophilic side chains are on the outside exposed to the
solvent, water, Globular protein are soluble in aqueous solution ( Garrette et al, 2005).
3) Membrane
protein: Are found in association with the various membrane systems of cells.
Membrane proteins have hydrophobic amino acid chains oriented outwards for
interaction with the non-polar phase within the membrane. They are insoluble in
aqueous solution but can be soluble in solutions of detergent (Garrette et al. 2005).
BIOLOGICAL FUNCTIONS OF PROTEIN
1) Many
proteins are enzymes: The largest classes of proteins are enzymes. These
enzymes are organic catalysts that speed up the rates of biological reaction.
Each enzyme is specific in its function and acts only in a particular reaction.
Virtually every step in metabolism is catalyzed by an enzyme (Garrette et al. 2005).
2) Control
of metabolism and Gene expression: A number of proteins do not perform any
obvious chemical transformation but nevertheless can regulate the ability of
other proteins to carryout their physiological functions such proteins are
referred to as regulatory proteins. Hormones are one class of regulatory
proteins examples include, insulin, pituitary, somatotropin, thyrotrophic
(Garrette et al, 2005).
3) Transport
and storage of molecules: Many small molecules and ions are transported by
specific proteins for examples;
a) Haemoglobin transport oxygen in
erythrocytes
b) Myoglobin (Mb) transport oxygen in
muscles.
c) Transferin carries iron in blood
plasma.
d) Ferritin store iron in the liver (Diribe
et al, 2002)
4) Cordinated
Motion: Muscle contraction occurs by the slide motions of two kinds of protein
filament called. Myosin and action. On the microscopic shade such coordinated
motion as the movement of the chromosome in mitosis and the propulsion of sperm
cells by their flagella also are produced by contractile assemblies consisting
of proteins ( Diribe et al, 2002).
5) Mechanical
support: some proteins contribute to the mechanical strength of some tissues in
the body for example a fibrous protein, collagen is responsible for the high
tensile strength of skin and bones in the body. (Diribe et al. 2002).
6) Immune
Protection: some proteins play a vital role in immune response in the body.
Antibodies are proteins with high specificity for recognizing and attacking
foreign substances in the body called Antigens. Proteins therefore, play the
important role of distinguishing between self and nonself in the living states
(Diribe et al, 2002).
LIPIDS
Animal
fats are found in meat, cheese, butter and egg yolk, plants fat occurs as oil
in fruits (palm oil) and seeds (sunflower seeds) and are used for cooking and
making margarine. Fats contains only carbon, hydrogen and oxygen but in
different proportion to the carbohydrate (Ramlingan, 2001).
A molecule of dietary fats typically
consist of several fatty acids (containing long chains of carbon and hydrogen
atoms) bonded to a glycerol. They are typically found as triglycerides (3 fatty
acids attached to the glycerol backbone) (Ramlingan, 2001).
Fats
may be classified as saturated or unsaturated depending on the structure of the
fatty acids involved. Saturated fats have all the carbon atoms in their fatty
acid chains bonded to hydrogen atoms, where as unsaturated fat have some of
these carbon atoms double bonded, so their molecules have relatively fewer
hydrogen atoms than a saturated fatty acids of the same length. (Ezeilo, 2002).
Unsaturated fatty acids are further classified as monounsaturated (one double
bond) or poly unsaturated (many double bond) (Ezeilo, 2002).
Furthermore, depending on the
location of the double bonding on the fatty acid chain, unsaturated fatty acids
are classified as omega-3 or Omega-6 fatty acids. 1 gram of fats can provide on
average 9kcal of energy (Ezeilo, 2002 and Ramlingan, 2001).
SOURCES
OF LIPIDS
Animal
fats are found in meat, milk, cheese, butter and egg yolk. Plant fats occur as
oils in fruits (palm oil) and seed (Sunflower seed). Rich Source of cholesterol
are egg yolk, meat and liver (Ezeilo, 2002).
FUNCTIONS OF LIPIDS
1) Energy
Storage: Triglycerides are an efficient form of energy storage that can be
mobilized when fuel is needed.
2) Transmission
of information in cells (Signal transduction): Lipid hormones, like steroids
and eicosanoids also mediate communication before the cells
3) Cellular
Metabolism: the fat soluble vitamins, A,D E and K are required for metabolism,
usually as coenzymes.
4) Structuring
cell membranes: The cell membrane constitutes a barrier for the cell and
control the flow of material in and out of the cell (Diribe et al, 2000).