Protein
 Essential for the life of every cell and the vital
functions in the body
 It is essential for growth and repair and the
maintenance of good health
 Requirements do not change very much
 Needs may increase with illness, infections,
surgery, or injury
 More than adequate intakes in Caribbean diets

Protein
 Protein is the second most abundant compound in
the body, following water.
 A large proportion of this will be in muscle with
significant proportions being present in skin and
blood.
 Protein is found in all body fluids, except bile and
urine.
 Carbon, nitrogen, oxygen, and hydrogen are
abundant elements in proteins, and there is a
smaller proportion of sulfur

Structure
 Proteins are large molecules made up of long chains of
amino acids. Amino acids are the building blocks of
proteins.
 There are many amino acids that combine in many
different ways to form many different types of proteins.
 The sequence of amino acids in each protein
determines its shape and function
 There are about 20 different amino acids commonly
found in plant and animal proteins. For adults, 8 of
these, have to be provided in the diet and are therefore
defined as ‘essential’ amino acids. These are:

Structure (essential amino acids)
Leucine
Isoleucine
Valine
Threonine
Methionine
Phenylalanine
Tryptophan
Lysine

Quality
 Proteins vary according to:
 their origin (animal or plant)
 their amino acid composition (particularly their
relative content of the essential amino acids) and,
 their digestibility
 High quality proteins are those that are readily
digestible and contain the dietary essential amino
acids in quantities that correspond to human
requirements.

Quality
 Proteins from animal sources have a higher biological value
(they contain all the essential amino acids needed by the
human body) than proteins from plant sources.
 A combination of plant proteins tends to have a
complementary effect boosting their overall biological value.
 In most diets, different proteins tend to complement
each other in their amino acid pattern, so when two foods
providing vegetable protein are eaten at a meal, such as a
cereal and pulses, the amino acids of one protein may
compensate for the limitations of the other, resulting in a
combination of higher biological value. This is known as the
complementary action of proteins.

Quality
 Most legumes tend to be deficient in methionine. Cereals,
e.g., tend to be low in lysine and tryptophan content,
although they do contain sufficient methionine. Thus,
the combination of different plant-based foods in dishes
such as rice and beans, or peanut butter and bread, results
in a complementary effect that raises the protein quality
compared with either food consumed alone. Therefore, it is
possible to obtain adequate amounts of high-quality protein
from a vegetarian or vegan diet.
 Yams are more useful as a source of protein than other root
crops and the protein complements the type in cereals so a
combination of yam and dumplings would also improve
protein quality of the meal.

Quality
 Digestion and absorption should always be
considered in evaluating protein quality.
 A protein can be predicted as being of good
quality on the basis of its amino acid score, but in
practice be of only poor quality because it is
poorly digested and/or absorbed.

Digestion, Absorption & Utilization of
Proteins
 All foods are broken down in the mouth but the
chemical digestion of protein begins in the
stomach.
 Protein digestion begins with the action of an
enzyme called pepsin. Proteins are broken down
into smaller peptides by the action of pepsin.
 Completed in the small intestine, several
enzymes from the pancreatic juice and the lining
of the intestine complete the breakdown of
protein into small peptides and amino acids.

Digestion, Absorption & Utilization of
Proteins
 Absorbed amino acids pass into the liver, where a portion of
the amino acids are taken up and used; the remainder pass
through into the circulation and are utilized by the tissues.
The hepatic portal vein is the vein that transports blood
from the digestive tract to the liver.
 Protein building and breakdown take place every day in the
body. Urea is formed from the breakdown of protein and is
carried in the bloodstream to the kidneys where it is excreted
in the urine.
 Most of the protein in the body is stored in muscle, and when
dietary intakes are low, the body will breakdown the protein
in muscle to meet its needs. When we take more protein than
the body needs, the excess is broken down, some ends up as
urea, the rest is used in the production of glucose.

Functions
 Protein is essential for many basic body functions:
 Helps in growth and development, and in repair
of muscles, bones, organs, blood, skin, hair
 Needed for repair of damaged tissues due to
illness or injury
 Needed to maintain the fluid balance within and
outside body cells. Proteins also help maintain
the balance between acids and bases within the
body fluids by accepting and releasing hydrogen
ions.
 Needed for blood clotting

Disease Risk
 Less severe deficiencies - due to low protein intake
or an imbalance in amino acid intake may result in –
 Reduced growth in children
 Loss of lean body mass in adults
 Anaemia (low Hb) in all age groups
 Weakened immune system increasing risk of infection
and subsequent health problems

Disease Risk
Protein and weight management
 Including a lean source of protein with a meal can help
to minimise feelings of hunger and decrease overall
energy intake.
 High protein, low carbohydrate diets claim to be
effective at producing weight loss despite a high fat
intake
 Such a diet remains contradictory to current healthy
eating messages. Also safety concerns about very-high-
protein diets that involved cutting out other food
groups and caution should therefore be exercised in
promoting them

Disease Risk
Heart Disease
 Foods rich in animal protein tend to be high in
saturated fat and sodium
 High intake of protein from red meat and dairy
products associated with greater risk of heart
disease
Kidney Disease
 Regular high protein intake increases work of
kidneys
 Not a cause of kidney disease but may worsen
existing kidney disease or hasten decline in function

Disease Risk
Adult bone loss
 High protein intake may be associated with increased
urinary loss of calcium
 This area of research is still controversial and the
findings have not been consistent.
Cancer
 Protein quality seems to matter more than quantity
 Eating a lot of red meat and processed meat is linked
to an increased risk of stomach & colon cancer

Food Sources
Animal protein
 Protein from animal sources contains the full range of
essential amino acids
 Sources include meat, fish, eggs, milk and cheese. Low
fat options are preferable as some can be high in
saturated fat.

Food Sources
Plant protein
 Complementary mixtures needed
 Sources: dried peas, beans, nuts, seeds and
cereals; smaller amounts in dark green leafy
vegetables, yam

Food Sources
Protein content in common foods
A 3-ounce cooked serving of most meat, poultry
or fish - about 18 - 21 grams of protein
 1 hard/soft boiled egg – 6.3 g
 1 oz of cheese – about 6-8 g
 1 cup of low-fat milk - 8 g
 1/2 cup of cooked dried beans – 8 g,
 ½ cup cooked rice – 2 g;
 1/2 cup peanuts – 18g;
 1 tbsp peanut butter- 4g.

Dietary recommendations
Protein requirements: Caribbean RDA:
The current RDA for adults (male & female) is 0.7 -
0.8 g protein/kg body weight/d with an extra 10
or 15 g recommended for pregnant and lactating
women, respectively
 Requirements are higher for growing children
(requirement per kg body weight) and in some
disease states
Percentage (%) of total calories:
• WHO: 10 -15%
• Caribbean – Proposed: 10% (approx. 56.3
grams protein)