four substances we refer to as food which can be used to produce
energy: carbohydrates, fats, proteins and alcohol. Alcohol however
is not considered a basic nutritional component of food.
1 gram of
Carbohydrates contains 3.75 calories.
1 gram of fat contains 9 calories.
1 gram of protein contains 4 calories.
1 gram of alcohol contains 7 calories.
(literally hydrates of carbon) are chemical compounds which act
as the primary biological means of storing or consuming energy;
other forms being via fat and protein. Relatively complex carboyhydrates
are known as polysaccharides.The simplest carbohydrates are monosaccharides,
which are small straight-chain aldehydes and ketones with many
hydroxyl groups added, usually one on each carbon except the functional
group. Other carbohydrates are composed of monosaccharide units,
and break down under hydrolysis. These may be classified as disaccharides,
oligosaccharides, or polysaccharides, depending on whether they
have two, several, or many monosaccharide units.
or saccharides (Greek sakcharon, "sugar") are simple molecules
that are straight-chain aldehydes or ketones with many hydroxyl
groups added, usually one on each carbon atom that is not part
of the aldehyde or ketone functional group. Carbohydrates are
the most abundant biological molecules, and fill numerous roles
in living things, such as the storage and transport of energy
(starch, glycogen) and structural components (cellulose in plants,
chitin in animals). Additionally, carbohydrates and their derivatives
play major roles in the functioning of the immune system, fertilization,
pathogenesis, blood clotting, and development.
carbohydrate units are called monosaccharides, such as glucose,
galactose, and fructose. The general chemical formula of an unmodified
monosaccharide is (C·H2O)n, where n is any number of three or
greater. All carbohydrates have a hydrogen to oxygen ratio of
2:1.Monosaccharides can be linked together in almost limitless
ways. Two joined monosaccharides are called disaccharides, such
as sucrose and lactose. Carbohydrates containing between about
three to six monosaccharide units are termed oligosaccharides;
anything larger than this is a polysaccharide. Polysaccharides,
such as starch, glycogen, or cellulose, can reach many thousands
of units in length.
biochemistry, fat is a generic term for a class of lipids. Fats
are produced by organic processes in animals and plants. All fats
are insoluble in water and have a density significantly below
that of water (i.e. they float on water.) Fats that are liquid
at room temperature are often referred to as oil. Most fats are
composed primarily of triglycerides; some monoglycerides and diglycerides
are mixed in, produced by incomplete esterification. These are
extracted and used as an ingredient.
with a lot of saturated fats tend to be solid at room temperature,
while products containing unsaturated fats, which include monounsaturated
fats and polyunsaturated fats, tend to be liquid at room temperature.
Predominantly saturated fats (solid at room temperature) include
all animal fats (e.g. milk fat, lard, tallow), as well as palm
oil, coconut oil, cocoa fat and hydrogenated vegetable oil (shortening).
All other vegetable fats, such as those coming from olive, peanut,
maize (corn oil), cottonseed, sunflower, safflower, and soybean,
are predominantly unsaturated and remain liquid at room temperature.
However, both vegetable and animal fats contain saturated and
unsaturated fats. Some oils (such as olive oil) contain in majority
monounsaturated fats, while others present quite a high percentage
of polyunsaturated fats (sunflower, rape).
protein is a complex, high molecular weight organic compound that
consists of amino acids joined by peptide bonds. Protein is essential
to the structure and function of all living cells and viruses.
Many proteins are enzymes or subunits of enzymes. Other proteins
play structural or mechanical roles, such as those that form the
struts and joints of the "cytoskeleton." Proteins are
also nutrient sources for organisms that do not produce their
own energy from sunlight. Proteins differ from carbohydrates chiefly
in that they contain much nitrogen and a little bit of sulfur,
besides carbon, oxygen and hydrogen. Proteins are a primary constituent
of living things.
carnivores protein is one of the largest component of the diet.
The metabolism of proteins by the body releases ammonia, an extremely
toxic substance. It is then converted in the liver into urea,
a much less toxic chemical, which is excreted in urine. Some animals
convert it into uric acid instead.
nutrition in humans
In terms of human nutritional needs, proteins come in two forms:
complete proteins contain all eight of the amino acids that humans
cannot produce themselves, while incomplete proteins lack or contain
only a very small proportion of one or more. Humans' bodies can
make use of all the amino acids they extract from food for synthesizing
new proteins, but the inessential ones themselves need not be
supplied by the diet, because our cells can make them ourselves.
When protein is listed on a nutrition label it only refers to
the amount of complete proteins in the food, though the food may
be very strong in a subset of the essential amino acids. Animal-derived
foods contain all of those amino acids, while plants are typically
stronger in some acids than others. Complete proteins can be made
in an all vegan diet by eating a sufficient variety of foods and
by getting enough calories. It was once thought that in order
to get the complete proteins vegans needed to do protein combining
by getting all amino acids in the same meal (the most common example
is eating beans with rice) but nutritionists now know that the
benefits of protein combining can be achieved over the longer
period of the day. Ovo-lacto vegetarians usually do not have this
problem, since egg's white and cow's milk contain all essential
amino acids. Peanuts, soy milk, nuts, seeds, green peas, Legumes,
the alga spirulina and some grains are some of the richest sources
of plant protein.
eight essential amino acids must be part of one diet in order
to survive and are needed in a fixed ratio. A shortage on any
one of these amino acids will constrain the body's ability to
make the proteins it needs to function.
foods contain different ratios of the essential amino acids. By
mixing foods that are rich in some amino acids with foods that
are rich in others, one can acquire all the needed amino acids
in sufficient quantities. Omnivores typically eat a sufficient
variety of foods that this is not an issue, however, vegetarians
and especially vegans should be careful to eat appropriate combinations
of foods (e.g. nuts and green vegetables) so as to get all the
essential amino acids in sufficient quantities that the body may
produce all the proteins that it needs.
deficiency can lead to symptoms such as fatigue, insulin resistance,
hair loss, loss of hair pigment (hair that should be black becomes
reddish), loss of muscle mass (proteins repair muscle tissue),
low body temperature, and hormonal irregularities. Severe protein
deficiency is fatal.
protein can cause problems as well, such as causing the immune
system to overreact, liver dysfunction from increased toxic residues,
possibly bone loss due to increased acidity in the blood, and
foundering (foot problems) in horses.
can often figure in allergies and allergic reactions to certain
foods. This is because the structure of each form of protein is
slightly different, and some may trigger a response from the immune
system while others are perfectly safe. Many people are allergic
to casein, the protein in milk; gluten, the protein in wheat and
other grains; the particular proteins found in peanuts; or those
in shellfish or other seafoods. It is extremely unusual for the
same person to adversely react to more than two different types