that supplied by the two other macronutrients.
Because fats are such an efficient form of energy,
they are stored by the body either in the abdomen
(omental fat) or under the skin (subcutaneous fat)
for use when the body needs more energy. Fats that
are in foods are combinations of four main types:
Saturated fats: These fats consist of fatty acid chains
that have no double bonds between the carbon atoms
of the chain. They are called saturated because they
are fully saturated with hydrogen atoms and cannot
incorporate more. They are solid at room temper-
ature and are most often of animal origin. Examples
are butter, cheese, and lard. These fats provide a
concentrated source of energy in the diet and build-
ing blocks for cell membranes and a variety of hor-
mones and hormone-like substances. An excess of
these fats in the diet however, is believed to raise
the cholesterol level in the bloodstream.
Monounsaturated fats: These are composed mostly
of monounsaturated fatty acids, meaning molecules
with one double-bonded carbon, with all the others
carbons being single-bonded. They are liquid at
room temperature. Examples are olive, peanut and
canola oil. They appear to protect against heart dis-
ease, in that they reduce blood cholesterol levels.
Polyunsaturated fats: These fats are composed mostly
of fatty acids such as linoleic or linolenic acids which
have two or more double bonds in each molecule, as
for example corn oil and safflower oil. They are also
liquid at room temperature and can be further divided
into the omega-6 and the omega-3 families. Polyunsa-
turated fats are thought to reduce the risk of coronary
heart disease. The omega-3 forms are believed to have
a positive impact on heart health and to play an
important role in brain and eye function. Oily fish
such as salmon, herring and mackerel are examples
of omega-3s, and they are also found in walnuts and
some oils like soybean and rapeseed.
Transfatty acids. Unsaturated fats come in different
chemical structures: a bentcisform or a straight
transform. When they adopt thetransform, they
are calledtransfatty acids. They are produced by the
partial hydrogenation of vegetable oils and present in
hardened vegetable oils, most margarines, commer-
cial baked foods, and many fried foods. An excess of
these fats in the diet is thought to increase the risk of
heart disease.
DescriptionThe three types of macronutrients do not have the
same chemical composition. When compared with
carbohydrates and fats, proteins are very different.
Fats largely consist of hydrocarbon chains, containing
75–85% carbon. Carbohydrates are roughly 50% oxy-
gen, and like fats, they usually have less than 5% nitro-
gen or none at all. Proteins, on the other hand, consist
of 15–25% nitrogen and about an equal amount of
oxygen. The three macronutrients are often found
together in most foods, but in varying amounts, or
alone in other foods. The Nutrition Facts labels pro-
vide a breakdown of the macronutrient composition of
various foods.Proteins
According to RDI, between 10 and 35% of calo-
ries should come from protein.
Foods that are a source of protein include:
Animal protein: Meat, poultry, fish, eggs, milk, cheese
and yogurt provide high biological value proteins,
because they contains all the essential amino acids.
Plant proteins: Plants, legumes, grains, nuts, seeds
and vegetables provide low biological value proteins.
However, combining proteins from different plant
sources in the same meal often results in a mixture
of higher biological value. Examples of such combi-
nations are: beans with rice, pasta or manioc, chick-
peas with bread, lentils with potatoes, vegetables
with cereals.Carbohydrates
According to the RDI, between 50 and 55% of
calories should come from carbohydrates and 20–35 g
dietary fiber per day should be taken by all those over
two years of age.
Sources of dietary carbohydrates include:
Monosaccharides: fruits, berries, vegetables and honey.
Disaccharides: table sugar, sugar beet, sugar cane
and fruits.
Polyols: Isomalt
Oligosaccharides: grains and vegetables
Starch polysaccharides: cereals, whole grains, rice,
pasta, potatoes, peas, corn and legumes.
Non-starch polysaccharides: dietary fiber such as
cellulose, hemicelluloses, pectins and gums.Fats
Overall fat intake should be no more than 30–35%
of total calories, with no more than 10% of calories
coming from saturated fats. This means that the remain-
ing 20–25% of calories should come from mono and
polyunsaturated sources. It is also recommended toMacronutrients