The Principle Nutrients In The Diet And Their Role In The Body |
- Food has two main functions which provide
- Chemical P.E. (starting point) for respiration
- Substances used in metabolism to produce/maintain cells and tissues
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Role Of Carbohydrates And Lipids In The Body |
Starch and Sugar |
Provide ≈80% of total chemical P.E.
Breast-fed infants obtain ≈40% of their chemical P.E. from lactose |
Non-starch polysaccharides (e.g. glycogen) |
Control appetite
Low levels in diet may cause
appendicitis, cancer of colon, haemorrhoids, constipation |
Lipids |
Source of chemical P.E.
Phospholipids are essential for plasma membranes
Essential fatty acids are precursors of other important substances |
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Simple Laboratory Techniques For Estimating Energy Content Of Different Foods |
- To determine the energy content of food (using a calorimeter)
- A known mass of food is fully burnt
- Under a boiling tube which is filled with a known volume of H2O
- Increase in temp of the H2O is measured
- ENERGY RELEASED = RISE IN TEMP OF H2O * VOLUME OF H2O * 4.2
- Experimental error due to incomplete combustion / heat loss
- More accurate results by reduced heat loss
- Water jacket → less loss of heat
- Sample burnt in O2 allows more combustion
- Copper coil transfers more heat to water
- Stirrer distributes heat evenly to area of thermometer
- Healthy diet requires right balance between carbohydrates and lipids
- Food rich in carbohydrates is an instant source of energy (→glucose)
- Tend to be bulky and contain large amounts of H2O
- Amount of energy released is low
- Food/drink rich in pure glucose is absorbed without digestion
- Lipid-rich food → amount of energy released is high
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Role Of Proteins In The Body |
Nucleic acid |
Genetic info |
Cells and tissues |
Growth and repair |
Enzymes and hormones |
Essential role in metabolic pathway |
Mineral ions |
Synthesis of compounds;
Carrying out functions;
Transmitting nerve impulses |
Essential amino acids |
Cannot be synthesised and must be present in diet |
Non-essential amino acids |
Can be synthesised from essential amino acids by transamination in the liver |
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Transamination |
- Essential amino acid A + keto acid B →
non-essential amino acid B + keto acid A
- Transfer of amino NH2 group from an essential amino acid to a keto acid
- Produces a non-essential amino acid and a keto acid of a different sort
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Role Of Vitamins With Respect To Vitamin D And Of Inorganic Ions Illustrated By Fe And Ca |
Vitamins |
Provided in fresh vegetables, meat, fish, eggs, fruit
Decrease appetite / minimises risk of constipation |
Vitamin D |
Involved in metabolism of calcium
Essential in the diet but required in small amounts |
Calcium |
- In bones, teeth, small amounts in tissues, body fluids
- Important for synapses
- During lactation, women tend to eat more → automatic increase in calcium intake |
Iron |
Synthesis of Hb, used by enzymes
≈30% in the body can be stored
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The Path Of Iron Through The Body |
- Absorbed from the gut and stored
- Used for physiological requirements (Hb, enzymes)
- Lost in blood, urine, rubbed off intestinal epithelial cells by food
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People Who Are Vulnerable To A Deficiency Of Iron: |
- People with a high physiological requirement for iron
- Children with late weaning and inappropriate infant food
- Growing people \ children and pregnant women
- Women of reproductive age / menstruation / loss of blood \ iron
- Old people / absorb iron poorly
- People who drink too much tea / tannin inhibits absorption of iron from gut
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Dietary Requirements Concept Of Basal Metabolic Rate BMR |
- Rate of metabolism when a person is at rest /
but awake
- Energy exhaustion to carry out essential activities that maintain live
- E.g. diffusion, breathing, pumping of blood
- NOT movement
- Measured in kJ kg-1 h-1 or kJ m-2 h-1
- Measured after meal at constant temp
- Temp may affect BMR → shivering
- Energy requirement at different levels of physical activity can be expressed in multiples of BMR
- BMR depends on number of metabolically active cells in a unit mass of the body
- Factors affecting BMR
- LARGER BODY MASS → more cells respire \ release energy
- LARGER SURFACE AREA → greater heat loss \ higher respiration to maintain core temp
- SEX → muscle has greater BMR then fat
- AGE → growth requires high energy amounts; muscle:body fat ratio decreases with age; biochemical reactions slow down, become less efficient
- FUNCTION OF BASAL METABOLISM → supply heat to maintain body temp above that of the surroundings
- BMR not helpful for total energy requirement (human is physically active the whole day)
- Physical activity ratio (PAR) is the energy being used in carrying out the activity concerned
to the basal metabolic rate
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Pattern Of Energy Expenditure And Protein Requirements Associated With Growth And Ageing |
| Protein Requirement |
- Growing people / production of new cells → youngest age group have highest requirement
- Pregnant woman / growing fetus and organs / lactation (milk is rich in protein)
- Adults / maintenances / synthesis of Hb, enzymes, hormones → lower requirement with age
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Glycogen Loading And The Enhancement Of Athletic Performance |
- High carbohydrate diet (long before exercise) / more glycogen in muscles / more can be broken down to glucose / prolonged rate of respiration / longer but not faster exercise
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Concept Of A Balanced Diet And Problems Which Arise From Vegetarian And Weight-Loss Diets |
- Balanced diet: correct amounts and properties of all/essential nutrients
- Fat in diet: makes foot tasty and → encourages eating / rather
stored than used as respiratory substrate / provides
essential fatty acids → must be in diet / provides more energy than the same mass of carbohydrates
VEGETARIAN DIETS
- Based on cereal grains, vegetables
- Total energy yield may be reduced (-)
- Must contain more protein to provide the supply for
essential amino acids
- Shortage of vitamin B12 and D, iron (→anaemia), zinc possible
WEIGHT LOSS DIETS
- Obesity → energy imbalance → energy intake with food > energy
expenditure in exercise
- Use of muscle and other tissue proteins for energy production - causing wasting
- SYMPTOMS: tooth decay / low blood pressure / constipation / menstruation ceasing
- INCREASED RISK OF: infections / vitamin and mineral deficiency diseases
- Ca2+ needs can be met by drinking skimmed milk
- Iron supply may need a supplement (-)
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Table 16-5-1: Dietary demands in pregnancy and lactation
| REQUIREMENT |
PREGNANCY |
LACTATION |
| Protein |
Growth of fetus, placenta, uterus, breasts |
High amino acid content of milk for growth of baby |
| Iron |
For fetal Hb and increase in mother's Hb and blood volume |
Synthesise of baby's Hb |
| Calcium |
Growth of fetal teeth and bones |
Growth of baby's bones (and teeth) |
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Influence Of IUDs And Oral Contraceptives On Menstrual Loss Of Iron |
- Intra-uterine contraceptive (IUD) affects amount of blood lost during menstruation
- Mean blood loss during menstruation before IUDs were fitted was 41cm³
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Table 16-5-2: Sample calculation
| Conc of Hb ≈ 13g per 100cm3 |
13 * 41/100 = 5.3g Hb lost |
| 5.3g Hb = 18.4g Fe over a 28-day cycle |
0.7mg day-1 of Fe lost |
| 0.8mg day-1 Fe lost from other causes |
Total loss of Fe = 1.56mg day-1 |
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- Average intake of Fe day-1 for women ≈12.1mg
- Only ≈15% absorbed → only 1.8mg day-1 taken into body
- This is a slight surplus compared with 1.56mg day-1 loss
- Mean blood loss during menstruation after IUDs were fitted was 90cm3!
- Iron loss and anaemia cause problems for women using IUDs, particularly if blood loss during menstruation was heavy or the diet was low in iron
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