Diet & Deficiencies (Cambridge O Level Biology)

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Balanced Diet

  • A balanced diet consists of all of the food groups in the correct proportions
  • The necessary food groups are:
    • Carbohydrates
    • Proteins
    • Lipids
    • Vitamins
    • Minerals
    • Dietary Fibre
    • Water
  • A balanced diet provides everything needed for successful growth and repair of tissues
  • There must also be enough energy that can be used for metabolic processes
  • There must also be enough roughage to maintain the function of the digestive tract
  • A diet can be unbalanced by having too little of a food group (called a deficiency) or by having too much (a surplus)

Food Groups Table

Food type Function Sources
Carbohydrate Source of energy Bread, cereals, pasta, rice, potatoes
Protein Growth and repair Meat, fish, eggs, pulses, nuts
Lipid Insulation and energy storage Butter, oil, nuts
Dietary fibre Provides bulk (roughage) for the intestine to push food through it Vegetables, whole grains
Vitamins Needed in small quantities to maintain health Fruits and vegetables
Minerals Needed in small quantities to maintain health Fruits and vegetables, meats, dairy products
Water Needed for chemical reactions to take place in cells Water, juice, milk, fruits and vegetables

Vitamin and Mineral Sources and Functions Table

Vitamin / Mineral Function Sources
Vitamin C Forms an essential part of collagen protein, which makes up skin, hair, gums, and bones. Deficiency causes scurvy. Citrus fruits, strawberries, green vegetables
Vitamin D Helps the body absorb calcium and so required for strong bones and teeth. Oily fish, eggs, liver, dairy products. Also made naturally by cells in sunlight.
Calcium Needed for strong teeth and bones and is involved in the clotting of blood. Deficiency can lead to osteoporosis later in life. Milk, cheese, eggs
Iron Needed to make haemoglobin, the pigment in red blood cells that transports oxygen. Red meat, liver, leafy green vegetables like spinach

Varying Dietary Needs of Individuals Table

Factor Dietary needs Age
Growth A higher proportion of protein Children
Activity levels More energy is required for movement as muscles are contracting more and respiring faster All ages
Pregnancy Extra energy and calcium are needed to support the growth of the developing fetus and the larger mass of the mother Pregnant women
Breastfeeding Extra energy and calcium still needed to make high-quality breast milk Breastfeeding women

Scurvy, Rickets & Anaemia

Scurvy

scurvy gums

Bleeding gums caused by scurvy

Centers for Disease Control and Prevention, Public domain, via Wikimedia Commons

  • Scurvy is the name for a severe vitamin C deficiency
    • It is caused by a lack of vitamin C in the diet for over 3 months
  • Its symptoms include:
    • Anaemia
    • Exhaustion
    • Spontaneous bleeding
    • Pain in the limbs
    • Swelling
    • Gum ulcerations
    • Tooth loss
  • It is a condition that was commonly seen in sailors between the 15th to 18th centuries
    • Long sea voyages made it very hard to access a ready supply of fresh produce
  • Scurvy can be treated with oral or intravenous vitamin C supplements

Rickets

rickets in 3 children

Rickets as seen in three children

Friends' Relief Mission, Vienna, CC BY 4.0, via Wikimedia Commons

  • Rickets is a condition in children characterised by poor bone development
  • Symptoms include: 
    • Bone pain
    • Lack of bone growth
    • Soft, weak bones (sometimes causing deformities)
  • Rickets is caused by a severe lack of vitamin D  or a lack of calcium in the diet
    • Vitamin D is required for the absorption of calcium into the body
      • Calcium is a key component of bones and teeth
  • Vitamin D mostly comes from exposure to sunlight but it can also be found in some foods (fish, eggs and butter)
  • The treatment for rickets is to increase consumption of foods containing calcium and vitamin D
    • Alternatively, vitamin D supplements can be prescribed

Anaemia

  • Anaemia is caused by a lack of iron in the diet
  • Iron is an important component of the blood pigment haemoglobin
    • Haemoglobin carries oxygen to all cells and tissues inside red blood cells
  • A lack of iron in the diet can cause a decrease in the number of red blood cells circulating in the blood
  • This can cause the person's skin to appear pale (called 'pallor')
  • Anaemia can also cause fatigue and exhaustion because there is not enough haemoglobin to carry oxygen to respiring cells all over the body

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Phil

Author: Phil

Expertise: Biology

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.