Research on Carbohydrates_ Lipids and Proteins

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Research on Carbohydrates_ Lipids and Proteins Powered By Docstoc
Carbohydrates provide energy for the human body and are actually the
primary source of energy.  Carbohydrates are the least expensive and
most abundant of all the energy nutrients.  Foods rich in
carbohydrates grow easily in most climates.  They are generally easy
to digest.  Carbohydrates provide the major source of energy for
people all over the world.  Carbohydrates provide half of the Kcal
for people living in the United States.  In some parts of the world
where fats and proteins are very scarce and expensive, carbohydrates
provide as much as 80% to 100% of Kcal.  Carbohydrates are named for
the chemical elements that they are made of – carbon, hydrogen, and
     Carbohydrates are divided into three
groups:  monosaccharide, disaccharides, and polysaccharides.
      Monosaccharides are also called, simple
sugars and are the simplest form of carbohydrates.  They are sweet
and require no digestion, and can be absorbed directly into the
bloodstream from the small intestine.  These include glucose,
fructose, and galactose.  Glucose is also called dextrose. It is the
form of carbohydrate that all the other forms are converted for
metabolism.  Dextrose is found naturally in corn syrup, honey,
molasses, sweet fruits and some vegetables.  Fructose, which is also
called levulose and fruit sugar, is found with glucose in many fruits and
vegetables, and in honey.  Galactose is a product of the digestion
of milk and is not found naturally.
     Disaccharides are sometimes called double
sugars.  They Are sweet and must be changed to simple sugars by
hydrolysis before they can be absorbed.  Disaccharides include
sucrose, maltose (often put into beer, baby formula and breakfast foods),
andlactose.  Sucrose is the form of carbohydrate present in
granulated, powdered, brown sugar, and molasses.  It is one of the
sweetest and cheapest sugars.  Its sources are sugar cane, sugar
beets, and the sap from maple trees.  Maltose is an intermediate
product in the digestion of starch within the body.  It is
manufactured from starch by enzyme action and it is not found naturally
and it is not as sweet as glucose or sucrose.
     Lactose is the sugar found in milk.  It
helps the body to absorb calcium.  It is different than most of the
other sugars because it is not found in plants.  It is less sweet
than the other single or double sugars.
     Polysaccharides are compounds of
monosaccharides.  Polysaccharides are often called “complex
carbohydrates”. Their solubility and digestibility vary. The
polysaccharides include starch, dextrins, cellulose, and glycogen.
     Starch is a polysaccharide found in grains and
vegetables.  Vegetables contain less starch because they have higher
moisture content.  The starch in grain is found mainly in the
endosperm or the center part of the grain.  This is the part which
the white flour is made.  The tough outer grain is called the
bran.  The germ is the smallest part of the cereal grain and is rich
in vitamin B complex, vitamin E, minerals, and protein.
     Before the starch in grain can be used it must
be broken down.  The heat and moisture of the cooking break down the
outer covering, making it more flavorful and more digestible.  Bran
itself is indigestible, but it is important that some bran is included in
ones diet because of the fiber it provides.
     Dextrins are digestible polysaccharides that are
the intermediate product of the hydrolysis of starch by enzymes or
     Glycogen is sometimes called “animal
starch” because it is the form in which carbohydrates are stored in
the body.  In the average, healthy adult there is approximately a 12
– 24 hour supply of energy stored in the liver and muscles as
glycogen.  Glycogen is converted back to glucose when the body needs
fuel for energy. 
     Cellulose is a fibrous form of carbohydrates
that makes up the framework of plants.  Humans cannot digest
cellulose and therefore it has no energy value.  Its use is because
it absorbs water as it passes along the digestive tract, thus providing
bulk for stool and
This prevents constipation.  The major sources of cellulose are bra,
whole grain cereals and fruits and vegetables.  Highly processed or
refined foods contain little cellulose because it is removed during
processing.  Highly processed and refined foods also do not take
away our hunger as well.
     Providing energy and heat is the major function
of carbohydrates.  Each gram of carbohydrate provides 4 Kcal (17
kj).  When carbohydrates provide energy, they spare proteins for
another essential use.  The other essential uses are the building
and repairing of body tissues.  This function is called the protein
sparing action of carbohydrates.  Carbohydrates are also essential
for metabolizing fats. 
     Monosaccharides, glucose, fructose and
galactose, or the simple sugars can be absorbed from the intestine
directly into the bloodstream.  They are then carried to the liver
where fructose and galactose are changed into glucose.  The blood
then carries the glucose to the cells.
     The disaccharides, sucrose, maltose, and
lactose, need an additional step of digestion.  They must first be
converted to glucose, before they can be absorbed into the bloodstream.
This is done by the enzymes, sucrase, maltase, and lactase.
     Polysaccharides are more complex and their
digestion varies.  After the cellulose wall is broken down, starch
is changed to an intermediate product, dextrin.  It is then changed
to maltose and finally, glucose.  Cooking can also change starch to
     The digestion of starch begins in the mouth
where the enzyme, ptyalin begins to change starch into dextrin.  The
next step takes place in the stomach where the food is mixed with gastric
juices.  Finally, it is in the small intestine where the digestible
carbohydrates are changed to simple sugars by enzyme action and then
absorbed by the blood.
     All carbohydrates are changed into the simple
sugar, glucose before metabolism can take place in the cells.  After
glucose has been carried to the cells, it can be oxidized. 
Sometimes, the volume of glucose that reaches the cells exceeds the
amount the cells can use.  Then some of the glucose is then
converted to glycogen and is stored in the liver and the muscles. 
When the intake exceeds the need, it is then converted to fat and stored
as adipose tissue or fat.
     The process of glucose metabolism is mainly
controlled by the hormone insulin, which is secreted by the islets of
Langerhans in the pancreas.  When insulin secretion is impaired or
absent, the glucose level in the blood becomes excessively high. 
This is called hyperglycemia and is usually a symptom of diabetes
mellitus.  In cases such as these a hypoglycemic agent stimulating
the production of insulin or insulin must be provided.  The
diabetics’ intake of carbohydrates must be controlled to balance
the insulin.  When blood glucose levels are unusually low, this is
called hypoglycemia.  A mild form can occur if one waits too long
between meals or because the pancreas secretes too much insulin.
     Oxidation of glucose results in heat and
energy.  With the exception of cellulose, the only waste products of
carbohydrate metabolism are carbon dioxide and water, making
carbohydrates a very efficient nutrient.  However; even too much of
a good thing can add fat. 
The Food and Nutrition Board of the National Research Council recommends
that people have at least 100 grams of digestible carbohydrate every
day.  It is estimated that most Americans eat a minimum of 200 grams
every day.  A diet seriously deficient in carbohydrate can cause
ketosis, which is an excessive breakdown of tissue protein and
dehydration.  Too many carbohydrates can cause tooth decay, gas in
the colon and irritation of the lining of the stomach.  A deficiency
of carbohydrates can result in weight loss and possibly a metabolic
LIPIDS    Lipids which are also called fats are oily
substances that are not soluble in water.  They are soluble in some
solvents, such as ether and alcohol.  Lipids provide a more
concentrated form of energy than carbohydrates.  Each gram of fat or
lipids contains nine kilocalories.  This is more than twice the
number as carbohydrates or proteins.  Lipids are made up of carbon,
hydrogen, and oxygen, just like carbohydrates, but with a much lower
proportion of oxygen
     Lipids provide energy and heat, but they are
also essential for the functioning and structure of body tissues. 
Fats are a necessary part of cell membranes.  They act as
carrier’s f essential fatty acids and fat soluble vitamins (A, D,
E, and K).  The fat stored in our body tissues provides energy when
one is unable to eat (today, during illness and long ago during winter or
famines).  Adipose tissue protects organs and bones from injury by
serving as a protective padding and support.  It also serves as
insulation from the cold.  Fats also make us feel full or satisfied
after meals.  Fat gives flavor to our other foods and slows the rate
of digestion, which staves off hunger.
     Lipid deficiency is rare in the United
States.  When a severe deficiency does occur eczema may develop
(inflamed and scaly skin).  Growth may also be retarded and weight
loss may occur when diets are grossly deficient in fats.
     Fats can be found in both plant and animal
foods.  Animal fats include:  fatty meats such as bacon or
sausage, lard, butter, cheese, cream, whole milk, and egg yolks. 
The richest sources of fats in plant food include:  cooking oils
made from sunflower, safflower, or sesame seeds, or from corn, peanuts,
soybeans, olives, or coconut.  Nuts, avocados, and chocolate also
contain fats. (Especially milk chocolates-dark chocolates are much lower
in fats). 
The components of dietary fats are fatty acids and glycerol.  While
there several fatty acids that the body needs; only linoleic acid is
considered essential to our diet. Sources of linoleic acid are corn,
sunflower, and safflower oil.  The other fatty acids can be
synthesized by the body.  Most natural fats are combined with
glycerol and are called triglycerides.
     Fats are generally classified as being
saturated, monounsaturated, or polyunsaturated.  This depends upon
the hydrogen content of the fatty acids that predominate their makeup.
     When a fatty acid is saturated, each of its
carbon atoms carries all the hydrogen atoms possible.  Generally,
animal foods contain more saturated fatty acids than unsaturated. 
These would include:  meat, poultry, egg yolks, whole milk, whole
milk cheeses, cream, ice cream and butter.  While it is true that
plant foods generally contain more polyunsaturated fatty acids than
saturated fatty acids, there are two exceptions, they are chocolate and
coconut. They contain large amounts of saturated fatty acids.  Foods
that contain a large amount of saturated fats are usually solid at room
     If a fat is monounsaturated, there is one place
among the carbon atoms of its fatty acids where there are fewer hydrogen
atoms attached than in saturated fats.  Foods containing
monounsaturated fats are olive oil, avocados, and cashew nuts.
     If a fat is polyunsaturated, there are two or
more places among the carbon atoms of its fatty acids where there are
fewer hydrogen atoms attached than in saturated fats. These foods
include:  vegetable oils, soft margarines whose major ingredient is
liquid vegetable oil, mayonnaise, fish, and peanuts.  Foods high in
polyunsaturated fats are usually soft or oily.
     Hydrogenated fats are polyunsaturated vegetable
oils that hydrogen has been added commercially to make them resemble
butter.  The process is called hydrogenation and it turns
polyunsaturated vegetable oils into saturated fats. (Ex: margarine).
There is no daily dietary requirement for fats.  The American Heart
Association recommends that people reduce fat intake from the current
average of 40 to 45 percent of total kcal to 30 to 35 percent.  This
would reduce the amount of saturated fats and cholesterol in ones
diet.  Excessive fat in ones diet can lead to obesity and/or heart
disease.  There are also studies that indicate an association
between high fat diets and cancers of the colon, breast, and uterus.
     Body cells are constantly wearing out and in
need of replacement.  Out of the six nutrient groups, only proteins
can make new cells and rebuild tissue.  Proteins are the basic
material of every body cell.  Body protein content is about 18% of
the average adults’ body weight.  Adequate protein intake is
essential for normal growth and development and for the maintenance of
health.  The word protein is of Greek origin and means “of
first importance”.
     Just as carbohydrates and lipids, proteins also
contain carbon, hydrogen, and oxygen, but in different proportions. 
Proteins additionally contain nitrogen and usually sulfur.  Many
also contain phosphorus, iron, and copper as well as other mineral
elements.  Each gram of protein provides 4 kcal (17 kj).
The primary function of proteins is to build and repair body
tissues.  Proteins are important components of hormones and
enzymes.  They play major roles in the regulation of the body
processes of digestion and metabolism.  They can provide energy if
and when the supply of carbohydrates and fats is not sufficient.
Proteins are made up of chemical compounds containing nitrogen that are
known as amino acids.  These amino acids are sometimes called the
building blocks of proteins.  Scientists have identified 22 amino
acids but found only nine of them to be essential to humans.  An
essential amino acid is one that is necessary for normal growth and
development and must be in ones diet.  A nonessential amino acid can
be produced by the body if an adequate supply of nitrogen is provided in
the diet.  Proteins containing essential amino acids are called
complete proteins.  A complete protein can build and repair tissue.
     An incomplete protein lacks one or more
essential amino acid and therefore; cannot build tissue without the help
of other proteins.  If one eats more than one incomplete protein at
the same meal they may combine to provide the essential amino acid that
is missing in the other.  A combination may therefore; provide all
nine essential amino acids.
Proteins are found in both plant and animal foods.  Animal food
sources provide the highest quality, or complete proteins.  These
include meats, fish, poultry, eggs, milk, and cheese.  Proteins
found in plant foods are incomplete proteins and are of lower
quality.  Even though this is true, plant foods are very important
sources of protein. Examples of plant foods containing protein are corn,
grains, nuts, sunflower seeds, sesame seeds, and legumes such as soy
beans, navy beans, pinto beans, split peas, chick peas, and
     Plant proteins can be used to make textured
protein products called analogs.  These products are made by
extracting the protein from plants (usually soy beans), and spinning it
into fibers of nearly pure protein.  The fibers are colored,
flavored, and shaped into a product that resembles and tastes like
meat.  It increases the protein content of the food to which
it’s added and can also be used as an economical meat replacement.
     The mechanical digestion of protein begins in
the mouth where the teeth grind the food into small pieces. 
Chemical digestion begins in the stomach.  Hydrochloric acid
prepares the stomach so the enzyme pepsin can begin its task of reducing
proteins to polypeptides or partially digested proteins.  After the
polypeptides reach the small intestine, three pancreatic enzymes
(trypsin, chymotrypsin, and carboxypeptidase) continue chemical
digestion.  Intestinal peptidases reduce the proteins to amino
acids.  After digestion, the amino acids in the small intestine are
absorbed by the blood and carries to a;; body tissues.
     All essential amino acids must be present to
build and repair the cells needed.  Surplus amino acids are sent
back to the liver where they are broken down by splitting off the
nitrogen.  The remaining parts are used for energy or converted to
carbohydrate or fat or stored as glycogen or adipose tissue.  The
end products of the metabolism of amino acids are carbon dioxide, water,
and nitrogen.  The excess nitrogen is sent to the kidneys and
excreted in urea.  Urea is the main end product of human protein
     One’s protein requirement is determined by
size, age, sex, and physical and emotional conditions.  A large
person has more body cells to maintain than a small
person…etc….If digestion is inefficient, fewer amino acids
are absorbed by the body, thus raising the protein requirement. 
Extra protein is usually required after surgery, severe burns, or during
infections to replace lost tissue and manufacture antibodies. 
Emotional trauma may cause the body to excrete more nitrogen than it
normally does, thus increasing the need for protein.
     The National Research Council of the National
Academy of Sciences considers the average adult’s daily requirement
to be 0.8 grams of protein per kilogram of body weight.
     When a person is unable to obtain adequate
protein for an extended period of time, muscle wasting will occur and
arms and legs become very thin.  At the same time, nutritional edema
can develop.  Edema is the retention of fluids in the body. 
This would make the person look swollen.  This water is excreted
when sufficient protein is eaten.  When one is deficient in protein,
one may lose appetite, strength, and weight.  Wounds may also heal
very slowly.  Patients suffering from nutritional edema often become
lethargic and depressed.  This can be seen in grossly neglected
children, the elderly poor or incapacitated.  This is not something
that is common in the United States.  There are diseases caused by
grossly inadequate supplies of protein, but these are most often seen in
third world countries where there are long term shortages of both protein
and energy foods.
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