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BCH 282
Biochemistry of Nutrition
Objectives:
• To define nutrition and related words.
• To identify nutritional requirements.
• To understand Food pyramid.
• To list types of nutrients and relation to health.
• To define malnutrition and its classification.
• To list main malnutrition problems.
• To describe Obesity.
• Nutrition is defined as the science of
food and its relationship to health. Or,
• The process of making use of food.
• It is concerned primarily with the part
played by nutrients in body growth,
development and maintenance .
• Dietetics is the practical application of the
principles of nutrition; it includes the
planning of meals for the well and the sick.
• Good nutrition means “maintaining a
nutritional status that enables us to grow
well and enjoy good health.”
• Nutrients are substances (specific dietary
constituents) that are crucial for human life,
growth & well-being.
• Macronutrients (carbohydrates, lipids, proteins &
water) are needed for energy and cell
multiplication & repair.
• Micronutrients are trace elements & vitamins,
which are essential for metabolic processes.
CLASSIFICATION OF FOODS
•
Classification by origin:
- Foods of animal origin
- Foods of vegetable origin
•
Classification by chemical composition:
- Proteins
–
–
–
–
Fats
Carbohydrates
Vitamins
Minerals
CLASSIFICATION BY
PREDOMINANT FUNCTION
• Body building foods:
• -meat, milk, poultry, fish, eggs, pulses
etc
• Energy giving foods:
• -cereals, sugars, fats, oils etc.
• Protective foods:
• -vegetables, fruits, milk, etc
• Community Nutrition:
Identification of nutritional needs of population
groups and available resources.
• Nutritional Epidemiology:
It is the investigation of the relationship
between diet and disease.
Nutritional requirements
Recommended Dietary Allowances (RDA):
The level of nutrients considered to be adequate to meet the
nutritional needs of all healthy persons.
Knowledge of RDA is necessary to:
•
Assess the nutritional adequacy of diets for
growth of infants, children and adolescents.
•
Maintain health in adults of both sexes and
during pregnancy and lactation.
The adequate diet & Food
Pyramids
Food Group System:
•
Classifies food according to similarity in
nutrient content.
•
Foods placed in each group have a high
nutrient density.
Daily Food guide with Nutrient Pattern and Recommended
Quantity.
Group
Milk and Cheese
Key Nutrients
Calcium,
Protein
Phosphorus,
riboflavin
Meats, poultry,
fish, beans
Protein, Iron
Niacin, Thiamin
Red meat -> Zinc
Egg yolk and liver
-> Vitamin A
Dry beans and Nuts
-> Magnesium
Quantity
Comments
3 cups for
children 4 cups
for teenagers
2 cups for adults
Low-fat milk products
have generally all the
same nutrient content,
however they are
lower in calories and
vitamin A.
2 servings
Serving size: 2-3
ounces
1 ounce of meat
= 1 egg
or ½ cup cooked
beans
1 ounce = 30 gm
Legumes and nuts has
a lower biological
value than meat.
They can be combined
with animal or grain
products to increase
protein quality.
Cholesterol and
vitamin B12 are found
only in animal
sources.
Food Pyramid
Lessons from Food Pyramid:
1. Maintain a healthy weight.
Studies show that the healthiest range
for body weight is when the body
mass index (BMI) is about 17 to 22.
2. Eat good fats and avoid bad fats.
•
•
•
•
•
Good fats are the oils found in nuts, seeds,
grains and fish.
They are high in the unsaturated fats necessary
for good health.
Good fats should contribute 30 to 45% of the
total fat.
Avoid saturated fats (animal fats and tropical oils
e.g. coconut) to minimize the risk of heart
disease.
Trans-saturated fats are mainly found in
margarines and commercial baked foods.
3. Eat whole-grain carbohydrates. Why?
• whole-grain are more nutritious than refined
carbohydrates
• Being more slowly digested
• Place less stress on pancreatic insulin production.
• Sources of whole grain carbohydrates include
whole meal bread, whole wheat, brown rice.
• Avoid white bread, baked goods and pasta made
with white flour.
4. Avoid red meat as a protein source
and emphasize plant proteins.
• Red meat consumption is linked to a variety
of chronic diseases & increases the risk of
hip fracture.
• Animal proteins are usually packaged with
saturated fat.
5. Eat plenty of vegetables and fruits.
•
Potatoes are not included as a vegetable.
•
Dark green leafy vegetables, and fruit are clearly
beneficial.
•
A diet high in fruits and vegetables lowers blood
pressure and cholesterol and reduces the risk of
cancer.
6. Take a multivitamin daily.
•
This recommendation is insurance against
any inadvertent deficiencies.
Mediterranean Pyramid
Main types of Nutrients
Energy Supplying Nutrients:
• Protein
• Lipids
• Carbohydrates
Non-Energy Supplying Nutrients:
• Vitamins
• Minerals
• Water
PROTEINS
• Proteins are complex organic nitrogenous
compounds.
• They also contain sulfur and in some cases
phosphorous and iron.
• Proteins are made of monomers called amino
acids.
• There are about 20 different aminoacids which
are found in human body.
• Of this 8-9 aa are termed “essential” as they
are not synthesized in human body and must
be obtained from dietary proteins.
Protein Needs:
• Adults: 0.8 gm/kg body weight per day
• Excess protein is not used to build more muscle
– If the body needs energy, the extra amino acids
are used for energy
– If the body does not need energy, the extra amino
acids can be converted to fat and stored.
Sources:
• Complete proteins have all essential amino acids
(animal sources)
• Incomplete proteins lack one or more essential amino
acids (plant sources)
Functions of Proteins
• Body building
• Repair and maintenance of body tissues
• Maintenance of osmotic pressure
• Synthesis of bioactive substances and
other vital molecules e.g.
immunoglobulins
Lipids
•
•
Lipids include cholesterol and triglycerides
Fat is necessary for health
Functions
1. Main source of energy (9Kcal/g).
2. Spare protein.
3. Adipose tissue holds the body organs and nerves
in place.
4. Maintain body temperature.
5. Transportation of fat soluble vitamins.
Classification
• Saturated fat:
– Animal foods generally are rich sources
– Palm and coconut oil also are rich sources
• Monounsaturated fat
– Olives, peanuts, and canola oil are rich sources
• Polyunsaturated fat
– Corn, sunflower, cotton seed, and nut oils are rich sources
• Hydrogenated fat
Hydrogenated fat
• Hydrogenation process hardens liquid oils into more
solid margarine.
– It makes unsaturated fat in oil more saturated
– Also it produces an unhealthy type of fat called
“trans fatty acid”
• Saturated fat and trans fatty acids may be harmful to
health
• Baked products and fried foods are often made with
hydrogenated fats
Cholesterol
• Cholesterol is necessary for cell membranes and the
production of vitamin D, bile, and certain hormones
• It is found only in animal foods
• High blood cholesterol levels are associated with
increased risk of heart disease
Fats yield fatty acids and
glycerol on hydrolysis
•
Fatty acid content of different fats ( in per cent)
•
•
•
•
•
•
•
•
•
•
Fats
Saturated Monounsaturated Polyunsaturated
fatty acids
fatty acids
fatty acids
Coconut oil
Palm oil
Cotton seed oil
Groundnut oil
Sunflower oil
Corn oil
Soya bean oil
Butter
92
46
25
19
8
8
14
60
6
44
25
50
27
27
24
37
2
10
50
31
65
65
62
3
Fat requirements
• The WHO Expert committee on Prevention
of Coronary Heart Disease has
recommended only 20 to 30 per cent of
total dietary energy to be provided by fats.
(<30%)
• At least 50 per cent of fat intake should
consist of vegetable oils rich in essential
fatty acids.
Carbohydrates
Functions:
1. Carbohydrate is the main source of energy, providing 4
Kcals per one gram
2. Carbohydrate is essential for the synthesis of certain
non-essential amino acids.
3. Necessary for normal fat metabolism.
4. Necessary for integrity of nerve cells.
5. Lactose allow growth of beneficial bacteria in the
intestine.
6. Important for normal elimination (excretion); fibers
Recommended carbohydrate intake is 55% to 65% of calories,
primarily from starchy foods
Classification of
Carbohydrates
1.
2.
3.
4.
Monosaccharides: glucose &fractose
Disaccharides: Sucrose (G + F)
Oligosaccharides (3-10).
Polysaccharides (11-1000)
a-Indigestable e.g. cellulose
b-partially digestable e.g.raffinose
c-Digestable e.g. starch
The inability of the body to metabolize
carbohydrates properly =DM
Fiber
• Indigestible plant material e.g. cellulose
• Dietary fiber is mainly non-starch polysaccharide
• It is found in vegetables, fruits and grains.
• Soluble fiber swells or dissolves in water
– Rich sources include apples, bananas, citrus fruits, carrots
• Importance:
– Reduces cholesterol absorption
– Slows absorption of glucose
Fiber
• Insoluble fiber remains unchanged in water
– Rich food sources include brown rice, wheat bran,
and whole grain products
• Importance:
• High fiber diet reduces the risk of heart disease,
diabetes type II, diverticulosis, hemorrhoids,
constipation, and possibly colorectal cancer
* Refined foods lose fiber-rich parts during processing
Non-Energy Supplying Nutrients
• Vitamins
• Minerals
• Water
Vitamins
• Regulate growth,
• maintain tissues, and
• help carbohydrates, proteins, and fats release
energy
• Provide no calories (energy)
• Needed in very small amounts
Classes of Vitamins
• Water Soluble: 8 different B vitamins and
vitamin C
• Fat Soluble: Vitamins A, D, E, and K
• Most healthy people do not need supplements;
vitamins can be obtained by eating a variety of
foods
– Supplementation can increase the risk of
consuming toxic high levels
Fat soluble vitamins
Vitamin A
• «Vitamin A» covers both:
– a pre-formed vitamin, retinol, and
– a pro-vitamin, beta carotene, which is converted to
retinol in the intestinal mucosa.
Sources:
– Retinol in liver, code liver oil & eggs (animal sources)
– Beta carotene: Coloured plants e.g. carrot, mango, apricot,
pumpkin,….. (plant sources)
VITAMIN
Sources:
• liver
• milk
• eggs
• spinach
• carrots
• tomatoes
• butter
A
Functions of Vitamin A
• It is essential for normal vision.
• It is necessary for maintaining the integrity and the
normal functioning of glandular and epithelial tissue
which lines intestinal, respiratory and urinary tracts as
well as the skin and eyes.
• It supports growth, especially skeletal growth
• It may protect against some epithelial cancers such as
bronchial cancers.
Vitamin D
• The nutritionally important forms of
Vitamin D in man are:
– Calciferol (Vitamin D2) and
– Cholecalciferol (Vitamin D3)
• Sources: Present in egg yolk + natural
(ultraviolet rays in sunlight).
VITAMIN
•
•
•
•
contains in:
liver
caviar
butter
D
Functions of vitamin D
• Intestine: Promotes intestinal absorption of
calcium and phosphorus
• Bone: Stimulates normal mineralization,
Enhances bone reabsorption, Affects
collagen maturation
• Kidney: Increases tubular reabsorption of
phosphate
Deficiency of vitamin D
Deficiency of vitamin D leads to:
• Rickets in children
• Osteomalacia in adults
Vitamin E
• Antioxidant- Protects RBCs from haemolysis.
• Present in wheat germ and green leafy
vegetables
Vitamin K
• Important for blood coagulation
• Present in leaves of plants + natural (flora).
• Deficiency causes haemorrhagic
manifestations.
VITAMIN
contains in:
• liver
• corn
• eggs
• vegetable oils
E
Water soluble vitamins
Thiamine (B1)
• Function: essential for the utilization of
carbohydrates.
• Present in brewer yeast, beans and legumes.
• Deficiency: Beri-beri
Deficiency of thiamine
• Beriberi may occur in three main forms:
– peripheral neuritis,
– cardiac beriberi,
– infantile beriberi, signs of peripheral
neuropathy.