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HBIO1 > Balanced Diet
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Balanced Diet

  • Energy Balance
    • Energy is obtained from food
      • Main energy from carbohydrates (glucose) and fats
      • Proteins are used for growth and repair first
      • Excess proteins is converted to energy
    • Out of balance
      • More energy/food than requiredobesity
      • Less energy/food than requiredstarvation
    • Types of carbohydrates
      • Intrinsic sugars: found within cells (fruits)
      • Extrinsic sugars: sugars that have been added to food (processed food)
      • Milk sugars: found in milk products
  • Basal Metabolic Rate (BMR)
    • Energy needed at rest (not when asleep!) for routine tasks of cells (excrete waste)
    • Factors that influence BMR
      • Age
        • Young > Old
        • Growth requires more energy → children, pregnant women (fetus)
        • Young and active people have more muscles than older people
      • Sex
        • Male > Female
        • Women have more adipose than muscle tissue
        • Muscles (work out) require more energy than fat cells (storage)
      • Body size
        • Tall and thin > short and obese
          • Tall and thin people have a large surface area but small volume
          • Loose heat quicker
          • Need more energy to maintain body temp
        • High body mass > Low body mass
          • High body mass → more cells that require energy
  • Starvation
    • No carbohydrates and fats are available in the diet
    • Body starts to break down its own proteins (muscles)

Function of


  • Polysaccharides (cellulose) that cannot be broken down by enzymes in the gut
    • Reduce absorption of carbohydrates
    • Reduce hunger
  • Prevent constipation (need plenty of water)
    • Speed up passage of food through intestine
    • Less time for toxins to accumulate
    • This reduces risk for colon cancer


  • Makes up 65% of our body weight/body mass
  • Requirements depend on
    • Intake of water by food
    • Body size
    • Physical activity
    • Environment (hot? cold?)
  • In normal conditions, 2L of water per day is recommended
    • Dehydration causes reactions inside cells to slow down
    • Overhydration causes dangerously low sodium levels [background reading]
  • How is water lost?
    • Breathing
    • Sweating
    • Excretions (urine, faeces)
    • Diuretics (alcohol, caffeine), which increase the amount of water in the urine


  • 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
    • Prevent appendicitis, colon cancer, haemorrhoids, constipation
  • Store and transport energy
  • Glucose is the main energy source in the brain


  • Source of chemical P.E. (energy reserve)
  • Phospholipids are essential for plasma membranes
  • Essential fatty acids are precursors of other important substances
  • Needed to absorb fat-soluble vitamins
  • Maintain body temperature


  • Required for growth and repair in cells and tissues (children require more!)
  • Carrier (change shape for different molecules) for water-soluble molecules such as glucose
  • Ion channels (sodium and chloride ions)
  • Pumps use energy to move water-soluble molecules and ions
  • Enzymes, which speed up chemical reactions at the edge of the membrane
  • Receptors enable hormones and nerve transmitters to bind to specific cells
  • Recognition sites, which identify a cell as being of a particular type
  • Adhesion molecules for holding cells to extracellular matrix


  • Often interact with enzymes to speed up metabolic reactions
  • Most are essential (must be absorbed from food)
  • Only vitamin D (skin) and vitamin K (gut bacteria) are non-essential (produced by body)
  • Fat soluble
    • Vitamin A: vision, growth, reproduction
    • Vitamin D: regulates calcium levels, bone formation
    • Vitamin K: blood clotting
  • Water soluble
    • Vitamin C: antioxidant, wound healing, synthesis of adrenaline, bone formation
    • Vitamin B12 and folic acid: cell division (low levels cause anaemia)
  • Supplements
    • Vitamins A and D (fat soluble)
      • Cannot be excreted from body
      • Only small amounts are needed, rest stored within liver
      • Excessive intake from supplements can cause liver damage
    • Vitamin C (and other water soluble vitamins)
      • Not stored - regular intake required for good health
      • Excess excreted in urine
    • In the UK, supplements are only useful for
      • Pregnant women (growth)
      • Elderly (less efficient absorption, less appetite)

Mineral Ions

  • Sodium: water balance (maintain osmotic pressure)
  • Chloride: maintain osmotic pressure, required for acid production in stomach
  • Potassium: abnormal levels cause abnormal heart rhythms
  • Calcium: bones and teeth, regulation of heartbeat, muscle contraction, blood clotting, nerve and brain function (important for synapses)
  • Phosphate: nucleic acids, ATP, phospholipids, bones and teeth
  • Iron: haemoglobin (low levels cause anaemia) and myoglobin formation

Healthy diet

  • EAT fruit and vegetables
    • 5 portions of fruit each day
    • Contain fibres (prevent constipation)
    • Contain vitamins (antioxidants)
  • MORE starch than sugar
    • Starch (pasta, rice, brown bread) releases glucose more slowly
    • Food with a high GI (food rich in sugar) is linked to obesity
  • RESTRICT salt and fats
    • Heart disease is caused by a diet
      • High in fat - increases cholesterol
      • High in saturated fats
      • High in salt - increases BP in hypertension (not in people with normal blood pressure)
    • Replace saturated with polyunsaturated fats
      • Omega 3 fatty acids (oily fish) protect from heart disease
  • Alcohol is not a risk factor for coronary heart disease (CHD)!
    • In fact, one glass wine per day reduces the risk of CHD

Gut Bacteria (Intestinal Flora)

  • Healthy gut flora
    • Harmless gut bacteria (symbiotic relationship)
      • Compete with harmful gut bacteria and reduce their disease-causing ability
      • Produce most of vitamin K
      • Strengthen the immune system
    • Babies are born without a gut flora
      • Pick up bacteria from surroundings
      • Breastfeeding helps to establish a healthy gut flora
  • Balance between harmless and harmful gut bacteria
    • Overgrowth of harmful bacteria or loss of harmless bacteria disturbs this balance
    • Can cause malabsorption and abdominal discomfort

Vitamin K

  • Used by E. coli for their respiration
  • Released into and absorbed from the gut after E. coli die
  • Deficiency is common in newborn (sterile gut flora!) → haemorrhagic disease of the newborn
    • Impaired blood clotting
    • Babies bleed easily from
      • Mucous membranes, such as nose
      • Intestines
      • Cuts in the skin
    • Treated with vitamin K (by mouth or injection)
  • Formula milk contains vitamin K
    • Vitamin K deficiency is more likely in babies who are breastfed
    • Takes time for E. coli to settle down within the gut

Probiotic Drinks

  • Contain "good" bacteria
    • Help to restore the balance of a healthy gut flora
    • Modify the immune system and reduce hay fever (1)
  • Only useful with an impaired gut flora caused by
    • Unbalanced diet
    • Inflammatory bowel disease (IBD)
    • Some antibiotics, which eradicate (kill) bacteria in the gut

Glycaemic Index (GI)

  • Effect of 50g carbohydrates on blood glucose levels
    • Thus, how much and how quickly glucose is released from food
    • 50g of glucose  → GI = 100
      • Low GI  (<55) - slow release of glucose/energy from food
      • High GI (>70)
    • Factors that affect GI
      • Branching of starch (more bonds → takes longer to digest → lower GI)
      • Fibres and vinegar (lowers pH) slow down absorption of starch
  • Low GI food (fruit, vegetables, pasta, rice)
    • Complex/intrinsic sugars
    • Contain large carbohydrates (starch)
      • Made up of many bonds that need to be broken
      • Blood glucose levels rise and fall slowly
      • Glucose is converted to glycogen (storage compound) in the liver
      • Keeps blood glucose levels constant
    • Prevents disease and improves control of blood glucose in diabetics
  • High GI food (Lucozade, white bread, croissants, candy)
    • Simple/extrinsic sugars
    • Contain small carbohydrates (glucose)
      • Easy to digest and quickly absorbed from the gut
      • Rapid and prolonged rise of blood glucose levels
      • This releases large amounts of insulin from the pancreas
      • Not enough time to convert all glucose to glycogen
      • Glucose is stored as fat instead (→obesity)
    • High glucose levels can damage arteries (atherosclerosis)
    • Sharp rise of insulin may cause sudden drop of blood glucose
      • Stimulates hunger (→obesity)
      • Tiredness
      • Loss of concentration

Glycaemic Load (GL)

  • Better indicator than GI alone
    • Small amount of high GI food has same effect as high amount of low GI food
    • Takes into account complexity (GI) and amount of sugar in food
  • GL = grams of carbohydrates x [GI / 100]
    • High GL (>20)
    • Low GL (<10)

Diet and Disease

Processed Foods

  • Raw food (bread, cereals, biscuits, cakes, pastries) is altered to improve its taste
  • Account for 75% of children’s salt intake
  • Rich in salt, simple sugars and fat (→obesity)
  • Food labels identify unhealthy food
    • Traffic light system
      • Red = high amount
      • Yellow = medium amount
      • Green = low amount
    • Guideline daily amounts (GDAs) system
      • Labels show amounts in one serving
      • Those are compared to guideline daily amounts

Food Additives

  • Given an E number when it has passed safety tests
  • Make food
    • Taste nicer (flavour enhancers, such as glutamate)
    • Look nicer (colourings, such as caramel)
    • Last longer (antioxidants, such as vitamin C)
    • Prevent bacterial growth (preservatives, such as sulphur dioxide)
  • Some people are intolerant to glutamate and, hence, most food products!


  • BMI > 30 // BMI = body mass (kg) / height² (m²)
  • Eat more energy/food than required
    • Lack of exercise
    • Unhealthy diet
  • Risk factor for type 2 diabetes
  • Obesity and diabetes → strong risk factor for heart disease, stroke, hypertension
  • Risk for cancer
    • Obese patients suffer from more inflammation than the normal population
    • Inflammation increases cell turnover
    • Higher chance for mutations that can cause cancer
  • Risk for fatty liver disease
    • Fat may deposit within the liver - can be reversible!
    • In 1%, this may progress to inflammation of the liver (risk for liver cancer!)
  • Risk factor for developing osteoarthritis and rheumatoid arthritis
    • Weight damages joints and bones over time

Type 2 Diabetes

  • Failure of blood glucose regulation
  • Cells have become insensitive to insulin
  • Prolonged, high blood glucose levels causes
    • Heart disease
    • Blindness
    • Nerve damage
    • Foot ulcers

Isotonic Sports Drinks (Lucozade)

  • Isotonic means same water potential as blood plasma
  • Heavy exercise for prolonged time
    • Higher sweat production → loss of inorganic ions and water
    • Higher rate of respiration → loss of glucose
    • Body reserves are lost and performance decreases
  • Isotonic drinks replenish ions (electrolytes), water and glucose (energy)
    • Increase performance
    • Prevent dehydration
  • Drinks are beneficial in moderate amounts after heavy exercise
  • Contain high levels of glucose - dangerous in diabetes!
  • Drinking more water OR sports drinks than fluid lost during heavy exercise
    • Can cause dangerously low sodium levels! (2)
    • Water starts to move into cells
    • Brain cells swell but cannot expand due to bony skull
    • This causes vomiting, headache, confusion, coma, or even death
  • (1) Ivory K, Chambers SJ, Pin C, Prieto E, Arqués JL, Nicoletti C. Oral delivery of Lactobacillus casei Shirota modifies allergen-induced immune responses in allergic rhinitis. Clin Exp Allergy. 2008 May 28.
  • (2) Dugas J. Sodium ingestion and hyponatraemia: sports drinks do not prevent a fall in serum sodium concentration during exercise. Br J Sports Med. 2006 Apr;40(4):372.