Proteins

ProteinsCompounds composed of carbon, hydrogen,

oxygen, and nitrogen and arranged as strands of amino acids

They are vital cellular working molecules. Without them, life would not exist.

Constitute approx. 20 % of body weightProteins are macromolecules. They are constructed

from chains of amino acids (peptides) A typical protein contains 200–300 amino acidsSome are much smaller peptides and some much

larger (the largest protein found in skeletal and cardiac muscle)

ProteinsProteins are available as:working proteins

(enzymes, antibodies, hormones, cellular “pumps”…)

structural proteins (cell membranes, tendons, ligaments, muscles, bones, teeth, hair, nails…)

Amino AcidsBuilding blocks of protein molecules20 different amino acids occur in nature of

which 9 are essentialEssential amino acids Non-essential amino acids

1. Histidine2. Isoleucine3. Leucine4. Lysine5. Methionine6. Phenylalanine7. Threonine8. Tryptophan9. Valine

1. Alanine2. Arginine3. Asparagine4. Aspartic acid5. Cysteine6. Glutamic acid7. Glutamine8. Glycine9. Proline10.Serine11.Tyrosine

Amino AcidsEssential amino acids• indispensable amino acids• they cannot be synthesized by the body• they are required to be consumed in diet

Non-essential amino acids • dispensable amino acids• they can be formed in the body

Conditional amino acids• These are non-essential that are conditionally essential until

the metabolic pathways are developed enough to make those amino acids in adequate quantities (eg. in times of illness, stress or early childhood)

Protein Functions1. Growth and repair material: teeth & bones,

material in scar tissue and blood clots, ligaments & tendons.

2. Synthesis (manufacture) of certain substances- hormones, enzymes, antibodies, haemoglobin, blood clotting factors, plasma proteins

Enzymes: regulation of biochemical reactions

Protein FunctionsHormones: messenger molecules. Many

hormones are proteins such as insulin, glucagon and the thyroid hormone

ex: insulin

Protein FunctionsTransport molecules: Hemoglobin carries oxygen;

Lipoproteins carry lipids, etc…

Antibodies: body defense molecules against foreign substances. They are proteins secreted from white blood cells.

4. Fluid balance regulation in the body: in protein deficiency, Edema can be observed (disease condition characterized by swelling of body tissues caused by fluid leakage)

Protein Functions

Protein Functions6. Maintaining acid-base balance: blood proteins

act as buffers in order to maintain the pH conditions of the blood constant

Acidosis- excess of acid in the body fluidsAlkalosis- excess of base (alkali) in the body fluids

6. Energy source: Proteins can be used for energy in case there is insufficient fat and CHO. Yields 4 Kcal/g.

NB: there is no storage form of protein in the body

Protein Sources Animal Sources: Milk, meat, poultry, fish (complete proteins)

Plant Sources: Pulses & legumes, beans, nuts & oil seeds (incomplete proteins)

Protein QualityProtein qualityDetermines how well a diet supports the growth of children and the health of adults

Influenced byA protein’s digestibilityA protein’s amino acid composition

Protein QualityAnimal proteins

Animal Protein (High digestibility /quality)

Plant proteinsPlant Protein (Low digestibility/quality)

Protein QualityAnimal proteins

are usually of higher quality and contain all the essential amino acids

Complete Proteins(except the protein

Gelatin)

Plant proteins are of a lower quality since

they do not contain all the essential amino acids in their protein structure

Incomplete Proteins(except Soybean)

Protein ComplementationProtein quality is of utmost importance in poor

countries where people rely on plant proteins as the main source of proteins in the diet.

The concept of complementation: plant proteins can provide enough amounts of all essential amino acids when combined to complement each other →

The essential amino acids missing from one are supplied by the other ex: legumes + rice

Body Protein NeedsProtein recommendations for infants, growing

children and athletes are somewhat higher than those for the general population

Even athletes in training do not typically need to increase their protein intakes because the additional foods they eat to meet their high energy needs deliver protein as well.

Body Protein NeedsDepends on:

Age (requirements decrease with age)Body size (increase with body size/weight)Pregnant and lactating women (higher than adults)Sick or immuno-compromised (higher) Recommendation is higher for infants and growing childrenAthletes

RDA for Adults: 0.8g/kg/day (15-20% of total daily calories).

RDA for body builders: 1- 1.2g/kg/day

Protein Energy Malnutrition

When people are deprived of protein, energy, or both, the result is Protein-Energy-Malnutrition (PEM).It is the most widespread form of malnutrition in the world today.

PEM strikes early in childhood: Marasmus and Kwashiorkor

PEM can touch many adult lives as well (AIDS, Cancer patients, Alcoholics, drug addicts, etc…)

Protein Energy Malnutrition

Marasmus Chronic inadequate food

intake Muscle wasting (heart

failure) Inadequate energy, vitamin,

mineral, and protein intake Person is shriveled and

lean all over

Kwashiorkor Too little protein to support

body functions Swollen belly and skin rash

are present Risk of infection Severe acute malnutrition Happen when weaning the

baby in developing countries

High Protein DietsHigh protein diets are being used to induce rapid

weight loss, however lifetime of excess protein intake (more than twice the RDA) is associated with many health risks:

Increased blood acidity (Ketosis)Kidney stones & renal failureCardiovascular disease (high in saturated fat)OsteoporosisDecreased vitamins, minerals, and fiber intakeEtc…

Vegetarian DietsPeople who opt to become vegetarian can still meet their daily protein requirement by carefully planning their meals and by knowing about protein complementation.

Vegetarian diets are often characterized by:Lower fat, cholesterol and calorie intake Increased vitamins, antioxidants and fiber intake

Positive health aspects associated with vegetarian diets:Lower incidence of obesity & CVDLower blood pressureLower incidence of diabetesLower cancer risksLower incidence of constipation

INFORMATION FOR YOUR INTEREST

Proteins

Amino Acids

Proteins

Each AA contains:- an amine group at one end (nitrogen – containing part) - an acid group at the other end (COOH)- a distinctive side chain

2) AMINO ACIDS

Side chain differs in size, shape and electrical charge → gives identity and chemical

nature to each AA

Proteins

Proteins: CompositionPeptide bond

Proteins

Protein ComplementationComplementary foods Examples Legumes/beans/pulses

+ grains (rice, corn, pasta)

(Chickpeas, lentils, beans) + rice

1 plant protein +

An animal protein source