Lecture 2 Dietary Carbohydrates & Proteins
Transcript of Lecture 2 Dietary Carbohydrates & Proteins
Nutrition and HealthLecture 2
Dietary Carbohydrates & Proteins
Ain Shams University, Faculty of MedicineDepartment of Medical Biochemistry & Molecular Biology
Prof. Reem M. SallamDr. Asmaa mohamed
Department of Medical Biochemistry & Molecular Biology
Faculty of Medicine, Ain Shams University
1.Determine the quality of proteins and methods to improve it
2.Define the nitrogen balance (zero, positive, negative)3.Identify protein energy malnutrition and its types4.Define different classes of dietary lipids5.Determine the metabolic effects of different dietary
lipids in human health and disease6.Determine the harmful effects of essential fatty acids
deficiency
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Quality of proteins
It is a measure of its ability to provide the essential amino acids (AAs) required for
tissue maintenance.
Protein Digestibility-Corrected Amino Acid Score (PDCAAS):
The highest -quality dietary protein has
PDCAAS of 1
Used to balance the intakes of poorer-
quality proteins with high-quality dietary
proteins.
Digestibility of the protein.
Essential AA content of protein
Standard used to evaluate protein quality Based on:
Quality of dietary proteins according to their sources
Proteins from animal sources
High quality proteins o eg: egg, milk, beef, poultry, fish
Contain all the essential AA in proportions similar to those required
for synthesis of human tissue proteins
Gelatin ( animal collagen ) exception of an animal protein that has a low
biologic value as it lacks several essential AA:. Gelatin’s PDCAAS =
0.08)
Proteins from plant sources
lower quality (relative to animal proteins)
eg: Whole wheat bread, kidney beans, soybean protein
Exception of a plant protein that has a high biologic value as it lacks
several essential AA: Soybean protein (its PDCAAS = 1)
What is protein complementation?
Combining two incomplete proteins that have complementary amino acid deficiencies : a mixture
with a higher biologic value.
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Rice
wheat
• no lysine
• rich methionine
Kidney beans
• rich lysine
• no methionine
high biological value
Protein complementation
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Combining proteins from different plant sources
• Nutritional value equivalent to animal protein
Combining animal proteins with plant proteins
What is the amount of nitrogen in protein?.
On average, there is 1 g of nitrogen in 6.25 g protein
Nitrogen balance
1-Nitrogen consumed = nitrogen excreted Nitrogen is excreted in urine (mainly), sweat & feces.- Normally healthy adults are in nitrogen balance
2- Positive nitrogen balance Nitrogen intake > nitrogen excretion In situations when:• tissue growth occurs, e.g. children, pregnancy,
• during recovery from an emaciating illness.
3- Negative nitrogen balanceNitrogen loss > nitrogen intake:• Inadequate dietary protein , Lack of an essential amino acid• during physiologic stresses (e.g. trauma, burns, illness, or
surgery)
RDA for proteins
Infants 2 g/kg/day (To support growth) .
Pregnant or lactating women
up to 30 g/day in addition to their basal requirements
Adults 0.8 g/kg of body weight (e.g. ~56g of protein for a 70-kg individual)
~1 g/kg of body weight (strenuous exercise on a regular basis; to maintain muscle mass)
Athletes
- Variable with the protein’s biologic value: - The greater the proportion of animal protein in the diet, the less protein is required.
In kidney disease: protein restriction is recommended (nitrogen is excreted mainly in the urine as urinary urea nitrogen)
In burns: increased protein intake is recommended.
Disease stated influence protein needs
RDA for proteins
Protein-energy (calorie) malnutrition (PEM) = Protein-energy undernutrition (PEU)
It is a spectrum of degrees of
malnutrition
Two extreme forms of PEM:
Kwashiorkor Marasmus
Both cause reduced ability to resist
infection (due to depressed immune
system) and Death from secondary infection
What are the Causes of Protein-energy malnutrition (PEM)?
In developed countries:
• Medical conditions that ↓ appetite or alter
how nutrients are digested or absorbed
• Hospitalized patients with major trauma or infections
(they may require intravenous
“parenteral” or tube-based
“enteral” nutrients’ administration)
• Malnourished children or elderly
In developing countries:
The main cause is Inadequate intake
of protein &/or calories
Protein-energy (calorie) malnutrition (PEM)Kwashiorkor Marasmus
Etiology - Protein deprivation is relatively > the reduction in total calories.- Protein deprivation →
↓ synthesis of visceral protein. - In developing countries in children after weaning at ~ 1 year of age (their diet consists predominantly ofcarbohydrates)
- Calorie deprivation is relatively > the reduction in protein.
- In children < 1 year (when breast milk is supplemented (or replaced) with watery gruels of cereals deficient in protein and calories)
Kwashiorkor Marasmus
Clinical picture
1. Stunted growth 2. Edema (due todecreased plasma [albumin]) 3. Skin lesions4. Depigmented hair 5. Anorexia 6. Enlarged fatty liver
1. Arrested growth2. Extreme muscle wasting 3. Loss of subcutaneous fat (emaciation) 4. Weakness 5. Anemia 6. NO EDEMA
Weight for age (% expected):
60-80% < 60%
Weight for height:
Normal or decreased Markedly decreased
Muscle and fat content
Decreased Markedly decreased
Protein-energy (calorie) malnutrition (PEM)
Kwashiorkor Marasmus
Clinical picture
1. Stunted growth 2. Edema (due todecreased plasma [albumin]) 3. Skin lesions4. Depigmented hair 5. Anorexia 6. Enlarged fatty liver
1. Arrested growth2. Extreme muscle wasting 3. Loss of subcutaneous fat (emaciation) 4. Weakness 5. Anemia 6. NO EDEMA
Weight for age (% expected):
60-80% < 60%
Weight for height:
Normal or decreased Markedly decreased
Muscle and fat content
Decreased Markedly decreased
Protein-energy (calorie) malnutrition (PEM)
Dietary Fats
1- Triacylglycerols (TAGs) (quantitatively the most important class of dietary fats)
2- Cholesterol: is found only in animal products, such as: - Liver and organ meat - Meat - egg yolk
3- Others, e.g. phospholipids
Double bound
Presence or absence of
double bonds
Number and location of
double bonds
cis/trans configuration
of double bonds
Dietary Fats
Fatty acids (FAs) have different biologic properties and are determined by:
Double bound
Presence or absence of
double bonds
Number and location of
double bonds
cis/trans configuration
of double bonds
Dietary Fats
Fatty acids (FAs) have different biologic properties and are determined by:
Functions of fat in our body:
Energy source (providing more energy than carbohydrates and proteins)
Help to protect vital organs and joints Insulate the body
Carriers for fat soluble vitamins
Cholesterol is the precursor for the synthesis of various steroid hormones and vitamin D in the body.
Other specialized functions
Fats and diseases:
increased risk for CHD
decreased risk for CHD.
Dyslipidemia (abnormal levels of plasma lipids)
Fats and diseases:
The effect of dietary cholesterol on plasma cholesterol level is <important than the amount and types of fatty acids consumed.
↑saturated fat in the diet ↑ the blood levels of total& LDL-
cholesterol → ↑CHD.
Dietary cholesterol has little influence
on plasma cholesterol level:
Mediterranean diet
It is a diet rich in:
Monounsaturated fatty acids (MUFA) (olive oil)
Polyunsaturated fatty acids (PUFA) (from fish oils, plant oils, and some nuts)
It contains seasonally fresh food (fruits and vegetables)
This diet is low in saturated fat.
Low in red meat
Mediterranean diet
↓coronary heart disease (CHD).
↑plasma HDL-C
↓TAG
↓ Total C
&LDL-C
Essential fatty Acids
Fatty acids that must be supplied in food as they cannot be synthesized in our bodies.
Linoleic acid 18:2(9,12) & α Linolenic acid 18:3 (9,12,15), are required for fluidity of membrane structure and synthesis of eicosanoids.
Deficiency of essential fatty acids is characterized by scaly dermatitis, hair loss, and poor wound healing
Components of dietary fat
1-Trans fatty acids
• Do not occur naturally in plants.
• Occur in small amounts in animal food
• Formed during the hydrogenation of liquid vegetable oils,
Present in:
• Margarine
• Commercial baked goods (cookies & cakes)
• Most deep-fried foods
Trans fatty acids
↑ the risk of CHD
↓ HDL
↑ LDL
Chemically classified as unsaturated FAs, but
behave more like saturated FAs.
Saturated Fatty acids
Examples: stearic and palmitic acids
TAG composed primarily of saturated fatty acids Solid at room temp
Present in Meat (beef, lamb, pork, chicken, shell fish) Milk & dairy products as cheese and butter. Some vegetable oils as coconut & palm oils. Chocolate
Saturated Fatty acids
↑ incidence of CHD, may predispose to prostate, colon cancer
little effects on
HD
↑ LDL
↑Total cholesterol
Mono-unsaturated Fatty acids
• Present in Olive Oil Example: Oleic acid 18:1(9)TAG composed primarily of FA with one double bond.
↓ incidence of CHD
↑HDL
↓ LDL
↓ Total Cholesterol
Poly-unsaturated Fatty acids
ω-6 PUFAs e.g. linoleic acid 18:2(9,12)
ω-3 PUFAs e.g. α-linolenic acid 18:3 (9,12,15
ω-6 PUFAs
TAG composed primarily of long-chain FA, with the 1st double bond beginning at the 6th carbon atom (when counting from the methyl end).
Present in Nuts, avocados, soybeans
Various oils (including sunflower, and corn oil
ω-6 PUFAs
↓ incidence of CHD
PG LT
↓ HDL
↓ TotalC & LDL
CProvide arachidonic acid precursor of Prostaglandin PG, Leukotrins
TAG composed primarily of long-chain FA, with the 1st double bond beginning at the 3rd carbon atom (when counting from the methyl end
Present in• Plant oils e.g. flaxseed or canola oils. • Some nuts (walnuts) • Fish oil (docosahexaenoic acid (DHA) &
eicosapentaenoic acid (EPA).
Dieticians recommend 2 fatty fish meals/week. In infant milk formulas to promote brain
development
ω-3 PUFAs
↓ incidence of CHD
↓ risk of sudden cardiac death.
Little effect on
LDL or HDL
↓ incidence of CHD
↓ risk of sudden cardiac death.
Suppress cardiac arrhythmias,
↓TAG
↓Tendency for
thrombosis
Lower blood
pressure
Anti-inflamm
atory
ω-3 PUFAs
Effects of dietary fats
Summary• The quality of a dietary protein is a measure of its ability to
provide the essential AA required for tissue maintenance.
• Animal proteins have a higher-quality than plant proteins, in general.
• Protein complementation: combination of proteins from different plant sources to result in improving the nutritional value
• Positive nitrogen balance: nitrogen intake > nitrogen excretion (due to tissue growth as in childhood & pregnancy, or during recovery from an emaciating illness)
• Negative nitrogen balance: nitrogen excretion > nitrogen intake (with inadequate dietary protein, lack of an essential AA, or during physiologic stresses such as trauma, burns, illness, or surgery).
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• Elevated levels of cholesterol or LDL cholesterol result in increased risk for CVD.
• Elevated levels of HDL cholesterol is associated with a decreased risk for heart disease.
• Dietary or drug treatment of hyper-cholesterolemia is effective in decreasing LDL, increasing HDL, and reducing the risk for CVD.
• Consumption of saturated fats is strongly associated with high levels of total plasma and LDL cholesterol.
• When substituted for saturated fatty acids in the diet, MUFA lower both total plasma and LDL cholesterol, and increase HDL.
• Consumption of fats containing ω-6 PUFA lowers plasma LDL, but HDL, which protect against coronary heart disease, are also lowered.
• Dietary ω-3 PUFA suppress cardiac arrhythmias and reduce serum TAG, decrease the tendency for thrombosis, and substantially reduce the risk of CVD
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Summary