We are what we eat - the biochemical basis of life is similar for all living organisms

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 required → obesity
    • Less energy/food than required → starvation
  • 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

Fibres

• 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

Water

• 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

Carbohydrates

• 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

Lipids

• 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

Proteins

• 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

Vitamins

• 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!

Obesity

• 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

References

• (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.